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Mineral Wool Insulation Isn’t Like Fiberglass

What you don’t know about mineral wool insulation will make you look stupid

Posted on Apr 8 2014 by Gregory La Vardera

If you are interested in green building, or call yourself a green building expert, then you should know about mineral wool insulation. If you have not seen mineral wool handled and installed, then you need to read this.

If you think that mineral wool batts are similar enough to fiberglass batts that you already know what you need to know about it, then you are a fool. And you still need to read this.

If you have already read some of my essays, you know that I am an advocate of using mineral wool insulation to improve the energy performance of the houses we build in the U.S. There are many reasons why I think that mineral wool is the best insulation for us here. Recently I find myself making my case for this repeatedly, so I thought it would be worthwhile to get it all down in one place and just point to it in the future.

Mineral wool is different from fiberglass

So why am I constantly explaining why I like mineral wool, and what's good about mineral wool? And why am I constantly saying, "No, that's not what mineral wool is like; rather, it is like this"?

It is because the green building community has almost universally decided that ol' fiberglass batt insulation is bad. There are good reasons for this, and we'll look at those, but the more obvious question is, What does this have to do with mineral wool?

The overwhelming assumption among those interested in green building is that mineral wool is just like fiberglass batts, at least in all the ways they feel fiberglass batts are bad. So if fiberglass insulation is bad, then they are convinced that mineral wool insulation will be bad, for all the same reasons. Its an easy conclusion to reach, but a lazy misunderstanding.

Not all batts are bad

The reality is that this is just not so. In fact this simply highlights the profound misunderstanding of what mineral wool insulation is like among green building advocates. The misunderstanding centers around the form of insulation: batts. The green building community has been very quick to condemn batts, when the problems that concern them actually revolve around fiberglass batts.

Let's make this absolutely clear: There is nothing wrong with insulation in the form of batts. Batts are a convenient way to package insulation for transport, handling, and installation, which is why it is the predominant form for insulation in the U.S.

However, there are legitimate reasons to criticize fiberglass batt insulation, the status quo in U.S. house construction. It's a brief list of reasons, so let's look at them.

Fiberglass batts have low R-values

First, low insulation values. That's right: fiberglass batts sold here in the U.S. don't provide as much insulation as they could. It's not that you can't make fiberglass in higher performance levels; in fact it is made and sold in Canada at higher R-values.

But the big fiberglass insulation makers are not ready to bring that high-R-value fiberglass insulation here to the U.S. How do I know? I've called them, spoken to their people about it, and they've told me they won't bring the high-R-value insulation to the States even though I said I wanted to spec it.

I say, shame on them. We should all take our business elsewhere.

Most fiberglass batt jobs are sloppy

Second: bad installations. Bad installations mean sloppy fitting of batts into stud cavities, over-compressing the insulation or leaving gaps that allow convection, sloppy trimming around obstructions, and any number of other installation sins that spoil the effectiveness of the insulation.

The installers are only partly to blame. The material is limp and fluffy, and because of this the handling, cutting, and placement requires more care to install well. It rarely gets that care; hence it is most often installed quickly and cheaply.

Where is the air barrier?

Third: bad air sealing and a bad vapor retarder. Well, what is that about anyway? Insulation is for insulating, not for air sealing — right?

Well, somewhere along the way, somebody had the bright idea to combine a vapor retarder with a fiberglass insulation batt. It turns two construction steps into one, and in theory saves labor and so saves money. The problem is that once you've had a bad installation as noted above, and cut the vapor retarder around electrical boxes, what you end up with does not seal well against air leaks or vapor diffusionMovement of water vapor through a material; water vapor can diffuse through even solid materials if the permeability is high enough. .

Hell, you say — I don't need my insulation to make an air seal, because I used that good ol' housewrap on the outside. Nope, nothing wrong with housewrap — but it provides no help with the air sealing you need at your vapor retarder.

The air seal in this case wants to be on the warm side of the wall, to prevent interior moisture from entering the wall cavity and condensing during the winter heating season.

The problem is the fiberglass, not the batt

Let's summarize the lesson here: What most green pundits blame on batt insulation is the fault of fiberglass insulation. While mineral wool also comes in batt form, it is a completely different product with different properties.

It does not suffer from any of the above problems of fiberglass, yet retains the best part: it's easy to handle, easy to install, and best of all, your labor force already knows how to do it. That is no small point.

Roxul is going after the residential market

OK, let's talk about mineral wool. I'm going to refer generally to "mineral wool," but as of this writing I have in mind the products of one manufacturer: Roxul. This is the only mineral wool manufacturer taking the residential market seriously in the U.S. right now.

Roxul sells its mineral wool in consumer-friendly packages, just as you would expect in a big box home improvement outlet. They are making their batts in sizes made to fit stud walls, clearly aimed at the market for building houses of wood, the very same market that fiberglass is sold to. This is important. Same kind of packaging, same kind of expectations, same kind of product experience.

They are putting their products into long-standing material distribution streams that every builder in the U.S. understands. It's available from the same sources, ready to be installed by the same people.

There are other mineral wool manufacturers out there, but they are not proactively pursuing the residential market. I'm not talking about them or their products. If your criticism of mineral wool revolves around your experience with some other product from some other time, then your concerns don't apply here and now. You should catch up.

Mineral wool batts have a higher R-value

So let's talk about insulation value first. In batts offered for 2x4 stud walls, mineral wool comes in R-15, while fiberglass comes in R-11 or R-13 (although it can be special ordered in R-15 in the U.S.). In batts offered for 2x6 walls, mineral wool comes in R-23, fiberglass comes in R-19 (and again, you can special order higher R-value, but only R-21).

Furthermore, mineral wool is available in batts that fit 2x8 framed walls, and these are R-30. Fiberglass is not offered in batts for 2x8 stud walls.

These are the products available now, today, in mineral wool. If you are interested in maximizing the energy performance of your walls, it's a no-brainer. Even if you changed nothing else about the way you build, you can improve the performance of your walls by switching to mineral wool.

Mineral wool batts are easier to install

Second, installations. You might think, “How can mineral wool batts be easier to install than fiberglass batts?” It's simple. Fiberglass batts are limp, soft blankets. They have to be hung and stapled into place or they will slump and leave gaps.

Mineral wool is dense and firm, and it friction fits into the stud space. People don't generally understand this, and this is why I am including photos. Mineral wool has form; it has a shape. If you pick it up it does not drape or fold; it retains its shape. (See Image #2, below) It is a block. This block, when shoved into a wall cavity — and I say shoved because it literally must be pushed into place — when shoved into place, fills the entire wall cavity (see Image #3, below). No gaps, no sags, no spaces. More importantly, no convection, no drafts, and no stapling.

You still have to cut the batts to fit

There is one caveat here: Just as with fiberglass, mineral wool must be cut to fit odd-spaced studs and triangular corners that may exist between framing members. However, this is much easier to do with mineral wool.

With fiberglass batts, you are actually told by experts to use a 2x4 stud as a straightedge while you cut the fiberglass batts with a sheetrock knife. You are expected to compress the fiberglass enough to cut through it with the short blade of the razor knife. And if you are doing it correctly, you trim the batt and kraft paper to different widths, to leave a tab so you can staple it up. Good luck.

Mineral wool is different. You can actually measure and cut mineral wool to size, like cutting a big block of wood. In fact, for carpenters this comes as second nature, because as you might expect they are quite good at measuring, and then cutting something to fit, when that something has a shape and can be understood like a piece of wood.

The cuts are made with large serrated knives — imagine a giant bread knife. (See Image #4, below.) So there is no compressing the insulation flat so you can cut through it. The mineral wool retains its volume while you cut through it with the long knife.

You don't cut against a 2x4, but rather you cut it on a purpose-made cutting table, which is just like a very large carpenter's miter box (see Image #5). It adjusts for the thickness of the insulation, and allows you to set precise angles for cutting to fit those odd spaces. (Read more about the insulation table here.)

Insulation cutting tables

The mineral wool cutting table, for me, is the eye-opener: the cold water in the face that made me realize that we never took insulation very seriously here in the U.S. Here we pull a 2x4 out of the dumpster, and use a razor blade holder to cut it on the floor deck. That's the best we can do.

Mineral wool is cut precisely to fill every void — quickly, accurately — providing complete fill of the wall cavity. Installations are easier, faster, and better than with fiberglass.

I'll say with some confidence that no other insulation product can fill a stud space so completely. No spray, no blown-in product, no blanket can fill a wall void as well as a proper installation of mineral wool insulation.

Smart vapor retarders

And third, air sealing. Mineral wool only comes in unfaced batts. No foil or kraft paper vapor retarders are offered. This means an independent vapor retarder must be installed. Simply said, this is the best way to create an airtight envelope for the house.

My favorite product in this regard is a variable-permeability membrane, a so-called “smart” membrane, because the permeability self-adjusts to suit conditions. An example is the MemBrain vapor retarder from CertainTeed. This is their branding of the smart membrane product made by their European owner, Saint-Gobain.

Another high-quality variable-permeability membrane is Intello Plus and DB+ by ProClima. This vapor retarder membrane has a low permeability level in dry conditions, but if the humidity level within the wall gets high, the material will open up to allow the moisture to dry to the other side. The ProClima Intello membrane is notable because it is well reinforced. It will not tear or split from stapling, and this tolerance of handling makes it easier to work with.

Include a service chase

Now, if you wish to increase the likelihood that you won't need to make any punctures in this airtight layer, then you should plan on a wall with an interior wiring chase, such as the U.S.A. New Wall that we've elaborated on here.

Your best chance for an airtight wall is if you don't puncture your air barrier with electrical work, outlet boxes, and switches. If you've not studied it before, when you are done here go read the U.S.A. New Wall article, and the Swedish Platform Framing article to see how all these come together to make a simple but high-performance wall.

That covers insulation value, installation, and air sealing issues. Mineral wool goes on to excel in other ways that contribute to my preference for this material.

It won't stay wet

Mineral wool is hydrophobic. From the dictionary: “Tending to repel or fail to mix with water.” If fiberglass insulation becomes wet, you end up with a wet lump of glass lint, with no insulation value to boot. Mineral wool, on the other hand, will not become wet.

In fact, water beads up and rolls off the surface of mineral wool. This promotes water draining and drying if the wall cavity becomes wet, rather than holding water like a sponge. Which would you rather have in your wall?

Addressing thermal bridging

One of the big issues with improving the performance of our walls is thermal bridging through the wall studs. The most popular way to overcome this has been to install insulation on the exterior of the wall, continuously, to insulate the studs from the cold.

The issue here is that rigid foam insulation has been the most common way to do this. The problem, however, is that the foam creates a vapor retarder, and the last thing you want is a wall with a vapor retarder on both faces.

So the practice has been to make walls with exterior foam insulation without interior vapor barriers. The foam must be thick enough to keep the dew point within the depth of the foam in order to prevent condensation within the wall cavity.

The problem here is that only the most general recommendations for these configurations can be made in the building code. Weather outside of the design limits can result in condensation. Highly humid interior conditions can cause condensation.

My opinion is that these walls are not resilient designs and are poor practice. A wall with a traditional configuration — with a vapor retarder on the interior — works in all conditions, even when the temperature or interior humidity goes beyond the design values.

My only caution is, if the home is to have air-conditioning, then it is very important to use a smart vapor control sheet, as mentioned above. These variable-permeability membranes will ensure the wall performs well during the cooling season when the vapor profileA vapor profile is an assessment of the relative vapor permeabilities of each individual component in a building assembly and a determination of the assembly's overall drying potential and drying direction based on vapor permeabilities of all of the components. The vapor profile addresses not only how the building's enclosure assembly protects itself from getting wet, but also how it dries when it gets wet. For a detailed treatment of this subject, see Building Science Corporation's article Understanding Vapor Barriers. of the wall is reversed.

The good news in this story is that mineral wool comes in configurations that can be used as exterior insulation in place of foam. These are very dense fiber panels that are strong enough to support siding and claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. material mounted over them in a manner similar to foam. The difference: mineral wool is vapor permeable, which means you can insulate on the exterior without trapping moisture in the wall.

Furthermore, the insulation value of these dense mineral wool panels approaches the performance of foam. Typically for XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. foam you would get in the neighborhood of R-5 per inch. Mineral wool will provide R-4.6 per inch.

And because of mineral wool's hydrophobic properties, it will not absorb moisture in this location, and in fact will promote the drainage and drying of rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. siding cavities.

Foam insulation brings other problems, such as dilemmas in flashing practices, and the dubious reliance on adhesive tape as a long term weather barrier.

Fire safety

Mineral wool simply makes wood stud construction safer. This is the same material that is used to fireproof steel members in commercial construction. Mineral wool will stand up to temperatures that will reduce fiberglass to a puddle of molten glass.

Mineral wool will increase the length of time that a wood-framed house will stand during a fire. It gives the occupants more time to exit safely, and firefighters a safer window of time to enter a burning home.

Summing up

Let's just go over some broad conclusions now. Mineral wool is a completely different material from fiberglass. They both just happen to fall in the broad classification of batts.

Mineral wool is available in higher insulation values than fiberglass. Mineral wool's rigid shape and ability to be measured and cut accurately enables it to fill stud voids more completely than any other insulation product, with less effort, and more speed.

Mineral wool fits into the building practices of 99.9% of America's builders with no need for new processes, extensive retraining, or changes to new subcontractors, new suppliers, and new business relationships.

Mineral wool is the easiest way for the vast majority of builders to step up their game and start building better.

Appendix 1: Concerns of green builders

Those focused on green building often immediately point to the presence of formaldehydeChemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified by the United Nations International Agency for Research on Cancer (IARC) in 2004 as a “known human carcinogen." in binders used in mineral wool. Formaldehyde-based resins have long been used in the "glues" that prevent fibrous insulation from coming apart. It's long been used in fiberglass, and is still used in many fiberglass products today. But it is clearly on the way out. Fiberglass batts from Knauf and Owens Corning are now available with alternate binders.

Mineral wool still contains a very small amount of formaldehyde-based binders. The wall insulation products from Roxul meet the GreenGuard Gold certification standard (formerly known as GreenGuard Children and School certification), which means they are consistent with products that are used in schools, day-care centers, or other environments where children spend significant periods of time. What this means is if you are a builder shifting from traditional fiberglass batts, this mineral wool will likely have lower formaldehyde emissions than what you used before.

If you are a green builder seeking to eliminate any formaldehyde, then you have other options.

On the matter of embodied energyEnergy that goes into making a product; includes energy required for growth, extraction, and transportation of the raw material as well as manufacture, packaging, and transportation of the finished product. Embodied energy is often used to measure ecological cost., the Roxul products now use from 75% to 93% recycled content, depending on the availability of the raw materials, and their facilities are “zero waste to landfill.”

If you are a green builder who can get the same performance from a material with less embodied energy, then great. If you are a builder considering shifting from fiberglass, the energy savings from the lifetime performance of the mineral wool will greatly exceed any difference in manufacturing energy of the fiberglass you use now.

Appendix 2: Predictions

Higher R-value insulation will eventually own the market here. CertainTeed, one of the biggest U.S. makers of fiberglass, is now owned by Saint-Gobain, a large producer of mineral wool in Europe. CertainTeed now has access to mineral wool, and could begin to sell it in North America as it gains market share.

Owens Corning, the other large American insulation maker which is highly vested in fiberglass, has purchased an American mineral wool manufacturer, Thermafiber, widening its offerings to include both mineral wool and fiberglass.

The third large American manufacturer of fiberglass insulation is Johns Manville, which has recently acquired an American mineral wool manufacturer, IIG (Industrial Insulation Group).

Not all of these companies are actively promoting mineral wool for residential building insulation, but it is remarkable that we find all of the major American insulation manufacturers vested in mineral wool.

Fiberglass has also been dogged by health questions. In 1984, fiberglass was classified as a "reasonably anticipated" carcinogen. This did not proceed to the next level, "known carcinogen," and in 2011, following more research, it was removed from this list.

Currently fiberglass is classified similarly to mineral wool, which is considered what is called "biosoluble." This means that these mineral fibers dissolve in contact with tissues, leaving no fibers to trigger disease. Whether fiberglass can shed its unhealthy reputation, or if it will be overtaken by mineral wool with its higher performance levels, has yet to be determined.

Editor's note: This article was adapted from a blog written by Greg La Vardera in 2012.

Greg La Vardera is an architect practicing in Merchantville, New Jersey, just outside of Philadelphia. His work has included the development of several off-site building methods and progressive design in catalog house plan publishing. He is now focusing on creating energy-efficient prototypes for production building based on Swedish precedents, as well as posting blog entries on his website.

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Image Credits:

  1. Smålandsvillan
  2. RepCon NW
  3. Randek AB

Apr 8, 2014 10:50 AM ET

by Debra Glauz

Great article. Sounds like a really good product for Wildland Urban interface zones.
"You still have to cut the batts to fit

There is one caveat here: Just as with fiberglass, mineral wool must be cut to fit odd-spaced studs and triangular corners that may exist between framing members. However, this is much easier to do with mineral wool."

When used in a stud bay, does mineral wool compress to take up different widths due to bent or warped studs. In other words, if one stud is bent to the left 1/8" or more and the other stud is bent to the right 1/8" or more would one then cut the batt to the largest width? If so, what it the tolerance?

Apr 8, 2014 11:18 AM ET

Edited Apr 8, 2014 11:21 AM ET.

@ Debra
by Gregory La Vardera

Its not rigid/stiff, but rigid/resilient. It relies on being slightly oversize for a snug fit.

Exactly how much - you should follow the manufacturer's lead - you can determine from measuring the uncut batt from out of the bag. It comes in standard widths for 16 & 24"oc, and is sized to fit snug in that spacing.

Apr 8, 2014 11:20 AM ET

not a hand saw
by Gregory La Vardera

BTW the "hand saw" in the picture at the top of the article is not a saw, but rather has a serrated blade like a bread knife, just in a large format like a hand saw. It is a Bahco ProCut insulation saw. Bahco is distributed in the US by Snap-On Tools.

Apr 8, 2014 11:26 AM ET

Edited Apr 8, 2014 11:33 AM ET.

Response to Gregory La Vardera
by Martin Holladay

I'm sorry if my caption to the photo was inaccurate. One might argue that a hand-held insulation saw is a type of handsaw. (On the manufacturer's website, Bahco calls this tool a "handsaw.")

But I agree with you that it is more accurate to describe this tool as an "insulation saw."

Apr 8, 2014 11:29 AM ET

by Malcolm Taylor

I have to ask: Why is this a good product for "Wildland Urban interface zones"?

Apr 8, 2014 11:49 AM ET

by Gregory La Vardera

No problem Martin - it was not identified in my original post. I just thought it was a worthwhile clarification. Its part of the theme here - they use special tools to make insulation installs better. We use 2x4s and sheetrock knives...

Apr 8, 2014 11:53 AM ET

Response to Malcolm Taylor
by Debra Glauz

It does not burn and we have a chance of building a fire safe ventilated rain-screen using Roxul comfort board. I realize this article is geared towards Roxul batts but I think using the batts in combination with out-board Roxul comfort board appears to solve some of the issues that may be caused by exterior foam and other cavity insulation products.

Apr 8, 2014 12:17 PM ET

Don't over-sell the higher R value.
by Dana Dorsett

R23 rock wool in a typical 25% framing fraction allowing R1 for gypsum and siding comes in at R15.2 whole-wall.

R20 (code minimum for US climate zone 5 under the widely adopted IRC 2009) would come in at a whole-wall R of 14.3, less than an R1 difference, about a 6% difference in heat flow.

R21 fiberglass is widely available at box stores (at about 2/3-3/4 the cost of R23 rock wool in my neighborhood) and comes in at R14.6 whole-wall. R21 fiberglass isn't dramatically floppier/squisher than R23 rock wool.

Everybody's favorite straw-man the R19 fiberglass isn't even code legal without another insulating layer. In a 2x6 cavity it performs at R18, with a whole-wall R of R13.6, but a 1/4" XPS fan-fold siding underlayment would bring it up to code performance.

If batts, rock wool is my first choice too, but the marginally higher R is the least of it.


"The foam must be thick enough to keep the dew point within the depth of the foam in order to prevent condensation within the wall cavity"

There is never condensation inside the wall cavity from interior moisture drives until the wood is actually saturated. The dew point of the entrained air in the cavity will never be higher than the temperature of the wood. When the wood falls in temperature it takes on moisture as adsorb (not liquid)and liquid water never form as on either the fiber or the wood until the wood is saturated, which takes more than just a few weeks of abnormally cold weather if the house is built with the IRC prescriptive minimums for exterior R for the climate zone. Those prescriptives should be considered minimums, but it doesn't take a whole lot more than the prescriptive minimums to make the assembly HIGHLY resilient (recommended), the air-sealing benefits of smart membrane vapor retarders notwithstanding.

Apr 8, 2014 1:01 PM ET

Nice article
by Gavin Farrell

I've always been a fan of mineral wool, now even more so. Good article!

Apr 8, 2014 3:23 PM ET

by Lucas Durand - 7A

I checked out Skärbord.
Looks like a great tool - I only wish I'd known about it sooner.

Apr 8, 2014 9:01 PM ET

by Malcolm Taylor

Good point!

Apr 8, 2014 9:18 PM ET

What I still do not know about mineral wool
by John Hansen

Even after reading this very informative post, I still do not know the most important fact to all home builders - the cost difference between mineral wool and fiberglass. (Mineral wool has always been more costly than fiberglass)
I would also like to hear your commentary or opinion on the labor factor that would be added by a single company who had trained professionals doing the work on each material.
I do not agree that the same tradesmen who install fiberglass batts have the right kind of experience or training to graduate from using a utility knife to using both a tape measure and a hand saw. I have never had an insulation company offer me both products.
In the case of insulation contractors who do fiberglass batts, my experience is that their cavalier "anything goes" approach to quality control leaves their installers at a profound disadvantage to anyone who has ever been properly trained to install mineral wool.
Also, the insulation companies that I am familiar with pay their workers on a piece rate. If they paid the same per batt for mineral wool as they do for a fiberglass batt job, then the outcome will surely be less effective than the manufacturers say it should be because I expect that properly installed mineral wool would take longer to install than a comparable job done with fiberglass. But the installers will do BOTH jobs equally badly in order to make their quotas.

Apr 9, 2014 11:19 AM ET

Answer to John Hansen #12
by Dana Dorsett

At recent local box store pricing the cost of R23 rock wool came in about 25% more than R21 HD fiberglass, both designed for 5.5" deep 2x6 cavities. On a small project I did about 15 months ago R15 rock wool was at cost-parity with R15 HD fiberglass.

It's not a hand saw, it's a serrated knife with a saw-type handle. There are no rocket scientists wasting their careers doing intensive training on how to use them. If anything it's EASIER to get a square-ish end cut with a purpose-made insulation knife than with a utility knife, and is recommended for use with fiberglass as well. I've personally found it easier & quicker to trim & split rock wool batts with a tight fit than mid-density fiberglass, but I can't say I have massive experience with either. It's slightly easier to deal with than HD fiberglass too, again from a fairly amateur perspective, with less than 10,000 square feet of lifetime installation experience with batts of any kind.

While the industry "typical" or "average" installation is pretty sloppy, there are batt installers capable of doing it right with either material, but the notion that it's more difficult or takes longer to do it right with rock wool is counter to experience.

Apr 9, 2014 11:33 AM ET

Rely to John Hansen
by Malcolm Taylor

It's too bad that, from your and others comments, it appears fiberglass installation in some areas is very poor. It isn't here. With all the time and diligence in the world i couldn't do as good a job as my installer does.
Extending your question as to whether installers will do as poor a job with mineral wool, I'd have to ask whether it is the material that causes the poor work or some other factor. If it isn't inherent to the material, which my installer shows is nor the case, then what is to stop any contractor from doing a sloppy job with spray foam or dense pack cellulose? The consequences of poor installs with those material are much more severe too.

Apr 9, 2014 5:45 PM ET

Mineral wool - great solution for fire breaks too!
by Mark Hays

Thanks Gregory for the excellent article -- which should help dispel common misconceptions about mineral wool vs fiberglass. A few suggestions:

> Fire breaks: Mineral wool is a great solution for the firebreaks required at the top of stud walls, and for the linear breaks required every 10' along a basement wall. If you follow Martin Holliday's excellent advice and run foam board along your basement wall, for example, you will need to include a firebreak that runs from the floor to the ceiling, every 10 feet. (Foam board cannot run continuously along the concrete basement wall.) Mineral wool is a great solution; just leave a gap in the foam board behind one of the studs, and pack it full. Similarly, mineral wool is easy to pack into the gap at the top of your stud bays, around pipes and wires, etc. -- to meet that firebreak requirement. Make sure you ask your inspector first, however. Some inspectors will only approve solid fireblocking with 2x lumber and 3/4" OSB.

> Unlike fiberglass, mineral wool acts like clay when you pack it into gaps and holes. You can shape it with your hands, and it stays put. You can pack it into the end of a ceiling joist bay to insulate the rim joist, for example, or around HVAC ducts.

> Wear gloves! Like fiberglass, the fibers in mineral wool can make your hands and arms itch.

In short, great stuff! It cost a bit more than fiberglass at my local HD -- and was worth every penny.

Apr 9, 2014 7:36 PM ET

Twice as hard to work with than Fiberglass
by Kye Ford

Even when I was still in the "dark ages" and using combinations of fiberglass and rigid insulation, I tried upgrading to mineral wool and found it twice as hard to work with than fiberglass. As a builder I still insisted on doing all my own insulation installation trying to be a meticulous as possible. Mineral wool is very difficult to work with, trying to cut around boxes, working around wire. Fiberglass you could at least cut a little tight around receptacles and the fiberglass would hug the boxes. Unless you were literally ready to spend a week scribing outlets your install would have gaps.

There's a better way its called cellulose. Fill all the voids. Anyone who has handled a lot of this product knows that it still falls short and is still just a batt insulation.

Don't fall for the hype.

Apr 9, 2014 8:34 PM ET

Sound attenuation
by Elizabeth Kormos

One more property of mineral wool is that it is a very good at sound insulation. We used dense packed cellulose for the exterior walls but did double stud walls and Roxul for soundproofing between our home offices and TV room.

Apr 10, 2014 9:49 AM ET

Mineral Wool & Fiberglass Options
by Ron Keagle

I am interested in doing much of my own construction work in order to achieve the highest possible quality. This would include installing the insulation. Because of my inability to install spray foam, plus a variety of other reasons, I have ruled out that type of insulation. I would consider cellulose, but hesitate because of probably needing to hire that work.

So, my preference has been fiberglass batts. I know all the complaints about that product, but I can overcome those drawbacks with 100% success, including a perfect installation. I will not use paper faced batts, but rather, rely on a separate vapor barrier. I find that fiberglass batts friction fit and hold themselves in place with no problem. I prefer to revert to double studs and a relatively low R-value insulation rather than maximizing stud width by using 2 X 8s and using the highest R-value insulation possible.

However, in a superinsulated, extra-thick wall, fiberglass batts do raise some strategy questions about combining batt thicknesses to fill the cavity, the density to use and its availability in various batt thicknesses, and the option of compressing it to raise its density.

My approach is to incorporate a service cavity as Mr. La Vardera mentions, which eliminates the need to pierce the vapor barrier with electrical boxes or to fit insulation around them. I also would have no piping or other obstructions within the insulation cavity in order to reduce the fitting of batts as much as possible.

So, within this overall approach, I welcome the addition of mineral wool as another batt insulation option. I have never used it, but I will certainly consider it going forward. Generally, I see it as a maximum-performance batt option. I too have wondered and inquired with insulation manufacturers about why they don’t come out with higher density fiberglass. Until they do, I see the mineral wool option moving in the direction I want to go. I have used a very high density fiberglass board, but have heard little about its application to building insulation. I have understood that it is intended for industrial applications. I don’t see why this could not be the future direction of high density fiberglass.

I had not known about the mineral wool batt cutting table shown by Mr. La Vardera, but I have been thinking about such a device for cutting fiberglass bats. I agree that the utility knife and straightedge used for cutting fiberglass is problematic, but the problem is in the very short length of a utility knife blade. To penetrate the batt with the utility knife blade, the knife body drags into the batt and pulls out chunks of insulation. A longer blade kitchen knife works much better. The ideal cutting table could cut miters, but this is a major challenge with fiberglass batts because they are cut in a state of compression. So the miter angle for a finished cut has to be modified for the cutting process in the compressed state of batt thickness.

I understand Mr. La Vardera’s point about the need to cut and fit mineral wool with the measuring and cutting mindset of a carpenter. I apply the same standards to cutting and fitting fiberglass batts, and believe that this is an essential requirement for a good installation job. Ignoring this requirement is the main reason why fiberglass batts are often considered to be poorly installed. However, I see no reason why careless installers will not achieve the same poor fit with mineral wool that they do with fiberglass.

Apr 10, 2014 10:00 AM ET

Edited Apr 10, 2014 10:02 AM ET.

Response to Ron Keagle
by Martin Holladay

You wrote, "The utility knife and straightedge used for cutting fiberglass is problematic, but the problem is in the very short length of a utility knife blade."

You may be interested in reading an article I wrote for the May 2003 issue of Energy Design Update, in which I review long-bladed insulation knives. I will post the article below as two jpg files.

[Click on the image below to enlarge it. The two images below look like one image, but they are really two images. If you click near the top, you'll get the first image. Then click near the bottom to get the second image.]


Comparing Insulation Knives 1.jpg Comparing Insulation Knives 2.jpg

Apr 10, 2014 10:34 AM ET

An 8" serrated bread knife works pretty well
by Dana Dorsett

... for cutting & trimming rock wool (& fiberglass) batts you can't find the purpose-designed tools. Insulation knives are available at box stores in my neighborhood.

Using utility knifes to cut fiberglass (especially HD fiberglass) is a bit of a hack, only to be done in a pinch, though still a commonly used method for low-density goods. Insulation knives work better though, on any density of batt.

Apr 10, 2014 11:41 AM ET

Response to Malcolm Taylor's comment #14
by John Hansen

You have a good way of addressing the question of what factors contribute to the poor quality that I see. I think there are a few issues.
1) The piece rate paid to the installers may work for simple walls and flat ceilings, but complex structures reduce the ability to achieve quality work at the same $/batt that the men would get paid. The need for speed that is created by paying piece rate results in batts simply being TORN rather than cut. Even the mineral wool that is stuffed around the drains under showers and tubs is seldom cut but just shredded by hand.
2) Insulation companies generally do not have a supervisor in the field checking quality. Rare is the company who has anything more than a dispatcher in contact with the installers. If there is a field supervisor, he is mostly concerned with whether there is enough material to finish the job, and when will the crew get to the next assignment.
3) Builders would NOT do QC inspections of insulation if it were not code required. Lazy builders cause many of their own problems when they think they can simply buy the job at the lowest price. And builders typically want the draft stopping done for "free" by the mechanical trades who drilled the holes, and then they leave that task out of the contract for the insulator.
4) Until recently, carpenters were seldom tasked with any responsibility for building a tight envelope, and they felt that it was all supposed to be done by the insulators. Many carpenters still do not "get it."
5) While the builder specifications might call for electrical boxes not be placed back to back on outside walls, negligence by the electrician and several other players make the task next to impossible for the insulators to make it any better than it already is. I have NEVER had any insulator bring up any issues that prevent them from doing a quality job. They just do not have the time to ask the builder to do any rework at this stage and the builders may have already had the drywall stocked. Here again, the attitude of the builders is as much at fault as the insulators. Builders do not want anything to slow them down, and that attitude sets the stage for all of the trades.

Apr 10, 2014 3:17 PM ET

Edited Apr 10, 2014 3:31 PM ET.

Swedish Platform Framming
by Terry Lee

Did anyone else read or notice the Swedish Platform Framing Gregory posted. Insulation is just a part of our issues. I didn't quite get the split lower sill? How many pieces are there and that is the only thermal bridge but a weak one? 3, 2 outer and a center "tongue and groove" So the center one is being used as an alignment tool for a prefabbed wall? If you don't run a chase you just strap the joist with a ribbon metal strap and you have a rim joist I didn't get that?

"Attached to the wall is a plywood plate, with the rest of the sill plate. This is like a tongue and groove joint, which allows our anchoring, and the sole plate of the wall above to be one in the same. It also permits the wall to be positioned precisely on the foundation when the sill plate is installed, not when a wall panel is dangling from a crane. The wall keys into the sill plate and its in the right position. If you were site building this you would use a solid sill. Inboard of this is a sill plate for the floor joists. Walls using an interior wiring chase tie the joists to the studs using the first 2x2 furring member(5). Walls without the interior wire chase use a rim joist, or ribbon tie let into the joists tops as is common with plate nailed floor trusses. Ok. Did we follow that? One sill plate. No sole plate. No rim joist insulation space. Wall batts continue all the way to the sill plate uninterrupted. The vapor retarder/barrier(6) also continues all the way to the wall sill uninterrupted. This is huge when you are trying to create a continuous vapor retarder, and huge that we can make a consistent insulation cavity all the way to the sill. And we are keeping count of thermal bridges, right -1 "

I wish I could read the first 3d picture text?

Apr 10, 2014 5:31 PM ET

Edited Apr 10, 2014 5:33 PM ET.

by Dennis Heidner

The workers in the photographs have sound protection equipment, but where are the safety glasses and mask to prevent inhalation of particles. The shirt on the worker in the lead photo isn't clean - he's obviously having stuff come off onto the clothing while cutting and handling the batts.

Apr 11, 2014 9:36 AM ET

Cutting insulation batts and boards
by Ron Keagle


Thanks for posting those insulation knives. They look like the right tool for cutting fiberglass. I have never cut mineral wool, so I wonder how a serrated knife works for doing that. For cutting XPS, I like to use a hand saw because it removes material so the blade can’t drag from the friction. I also use a hand held circle saw or table saw at times. That insulation cutting table appears to just be a guide for a hand saw or knife.

Apr 11, 2014 10:23 AM ET

Edited Apr 11, 2014 10:44 AM ET.

by Gregory La Vardera

I disagree with your dismissal of the higher density and r-value as an oversell. You can not get higher r-values without going to a foam product which then has undesirable impact on the vapor performance of the wall system. Its a no-brainer to use the higher value mineral wool. The additional cost is off-set easily by the better performance, and for the installer it is off-set by faster better quality installs.

Thank you for your account of adsorption, but not so much for your dismissal of the risks: "…which takes more than just a few weeks of abnormally cold weather …". You know well that the wood in the cavity will always be colder than the average temperate section through the assembly, and the studs may be experiencing adsorption to some degree during normal temperature ranges, and in a pre-or partially saturated state before entering an abnormally cold snap. That means it is more prone to moisture problems, mold growth, and decay. This is compounded in places like bathrooms that also experience out of range humidity. I maintain that this kind of assembly is not resilient.

The point is it really takes some analysis to get it correct when you do a wall system that relies on exterior foam insulation to control for condensation, or adsorption if you have to speak building science. Here lies the problem. The vast majority of houses built in the US never see an architect, never mind a building scientist. Advocating for these reverse vapor profile walls, whether you call them perfect walls or remote walls, or whatever is a recipe for failure when handed off to an industry that builds from model wall assemblies or prescriptions in the code. Assemblies with interior side vapor control in heating climates are simply more resilient.

Apr 11, 2014 10:26 AM ET

@John Hansen
by Gregory La Vardera

John, I've seen fiberglass crews take to mineral wool without loosing a step. I've handed them my Bahco knife and seen it immediately change their work flow, and the quality of their work. The contractor reported they finished the job with greater speed. I don't think my experiences are unique.

Apr 11, 2014 10:36 AM ET

@Ron Keagle
by Gregory La Vardera

The service cavity takes very little additional effort to install, and greatly speeds the main stud cavity installation, since it is now free of wires and pipes. Quality and speed goes up, and with another layer of insulation in the service cavity a thermal break is introduced.

You can build these assemblies with fiberglass, but I'd still stay away from the faced batts. The separate smart vapor sheet makes it so easy to establish your primary air-tightness layer between the service cavity and studs, and the Swedish Platform Framing shows the way to extend that all the way around the interior. So much easier than taping sheathing, and trying to make that air tightness transition from outside wall to interior ceiling.

Apr 11, 2014 10:38 AM ET

@ Terry Lee
by Gregory La Vardera

If you are not clear on any details of the Swedish Platform Frame contact me direct and I'll try to help. You might watch the associated video as it looks at the assembly in 3d and in some ways shows this better.

Apr 11, 2014 10:40 AM ET

@Ron Keagle
by Gregory La Vardera

That Bahco knife is also good for foam, and they claim it makes a lot less crumbs than toothed saws. There is a good video showing this on the Bahco web site. Seek it out.

Apr 11, 2014 10:48 AM ET

Response to Gregory La Vardera
by Martin Holladay

You wrote, "Advocating for these reverse vapor profile walls, whether you call them 'perfect walls' or REMOTE walls, or whatever, is a recipe for failure."

I'm sorry, Gregory, but I disagree. I'm not sure whether your broad statement is based on exaggeration or ignorance, but there is absolutely no evidence of problems with REMOTE walls -- while there are countless examples of problems with walls insulated with batts. It's all fine and good to describe the advantages of mineral wool insulation -- I tend to agree with you on most of your points -- but there is absolutely no evidence to support the idea that advocating the REMOTE approach is "recipe for failure."

Apr 11, 2014 12:04 PM ET

We will agree to disagree then (response to #25)
by Dana Dorsett

Sure, R23 is R3 better than code-min, but translates into R1 improvement in thermal performance. It's not the fault of the material, but needs to be clear to whomever is buying it that an R23 studwall is not a 15% improvement in thermal performance over a code-min R20 studwall. It's less than half the performance gain that the center-cavity R might imply.

I'm shocked and dismayed when people put R30+ closed cell foam in a 2x6 16" o.c. studwall, for a gain of about R2 in whole-wall performance over an R20 code min fiber solution. Yes, it's higher-R, but there is both cheaper & better performance enhancements. The upcharge for R23 rock wool over R21 HD fiberglass at recent pricing is nowhere near as egregious as the closed cell foam example. But it's still significant, while the thermal performance improvement isn't, which is why that uptick in R value isn't a good selling point. (I'm saying this as someone who would pay that upcharge every time, but not for the R-value, for other attributes of rock wool.)

It doesn't take a lot of analysis to come up with dew point calculations for exterior foam, in fact it doesn't take any calculation at all. IRC 2012 prescriptive minimums (spelled out in chapter 7: ) are sufficient. In US climate zone 5 at the same thermal performance, an R13 + 5 code min wall (or an R15 +5 of slightly better thermal performance) with no interior side vapor retarder other than standard latex paint is more resilient than an R23 2x6 wall with an interior vapor retarder- the sheathing stays warmer, and there is more drying capacity, despite the potentially lower vapor permeance of the exterior layers.

At 3-5 perms interior latex is still a pretty good vapor retarder for riding out the cold weather extremes- enough so that it's only the averages that count. The increased adsorption rates during a 1-week cold snap isn't going to materially affect the peak moisture content of the wood, and even a mid winter month averaging 5F colder than normal isn't going to cause a problem. Five consecutive winters where all 13 winter weeks averaged 5F colder than normal might, if you were dead-at the IRC prescriptive minimums, and on the cold edge of your climate zone. Exterior insulation works, and works BETTER than smart vapor retarders (WUFI, anyone?).

But more exterior-R is of course better, since it bumps the wintertime mean sheathing temp a bit further, and code-minimums is the crummiest assembly that you are legally allowed to build. The upcharge for another R4 of exterior insulation above the prescriptive minimums is on the order of 40-50 cents per square foot, and buys a HUGE amount of dew point margin, as well as an improvement in thermal performance uptick that is still cost effective in almost all utility markets. In a green-building blog discussion code minimum building assemblies are not the defaults, even if code-min is buildable using crummy/so-so/good/better/best-resilience methods.

Apr 11, 2014 8:00 PM ET

by Gregory La Vardera

There are countless problems with walls insulated with batts because they were built with kraft faced fiberglass which provides neither an air barrier or vapor control, or barely if installed well.

I am talking about wall assemblies installed with a continuous vapor control layer also serving as the air barrier. That is an assembly that can be batts, or other materials as well. This is not a batts vs exterior foam question, its interior vs exterior vapor control.

The other reason there are countless problems with walls insulated with batts is because of the huge installed base. There is no where near the installed base of Remote based wall assemblies in the US. I think you are making an apples to oranges comparison.

That fact is that Canadian building science went one way, Swedish building science went the other. The Canadians never had a good solution for the rim joist space, hence insulating outside it. The Swedes solved this, without adopting the counter intuitive move of vapor control to the outside. That is it in a nut shell. My opinion is one is a solution, the other is a hack.

Apr 11, 2014 8:09 PM ET

Edited Apr 11, 2014 8:13 PM ET.

by Gregory La Vardera

I don't find your comparisons fair, nor apples to apples.

An assembly with vapor control at the interior can also have exterior insulation, which improves the sheathing temp and bequeaths all of the resilient qualities you ascribe to exterior foam/vapor control.

OR you have the option to create a service cavity at the interior, which makes it so much easier to keep the vapor control layer free of holes, and hence the temperature of the sheathing is not really a concern.

And you can do both the exterior insulation and service cavity if you want the Best performance.

But I don't put much stock in the vapor control of latex paint when every outlet box and switch box makes it irrelevant. And time spend on air-tight drywall practices would easily pay for the service cavity which is a much more resilient approach, something that wont be compromised by casual remodeling in the future the way air-tight drywall (jumbo shrimp?) can be.

The fact is that the natural pressure in the housing industry is to put up as little of an expensive material like foam as possible - not to put up a little extra because it will perform that much better. The vast majority is code minimum, that's it, and less if they can get away with it. And at the scale of the climate zones which is how the code dictates foam thickness, there are plenty of opportunities for local climate, not to mention recent wild weather variations, to push an assembly beyond what the code has anticipated.

It seems there are many fans of this exterior foam approach on GBA, so I apologize for being so contrary. I see it as poor practice, and its discouraging to see it so highly recommended by such a popular source.

Apr 12, 2014 5:15 AM ET

Edited Apr 12, 2014 5:16 AM ET.

Response to Gregory La Vardera
by Martin Holladay

You wrote, "There is nowhere near the installed base of REMOTE-based wall assemblies in the US. I think you are making an apples to oranges comparison. That fact is that Canadian building science went one way, Swedish building science went the other. The Canadians never had a good solution for the rim joist space, hence insulating outside it."

I agree that there are many more walls in North America that are insulated with batts than there are insulated with the REMOTE system. But we have lots of data on how exterior insulation affects sheathing. Researchers have found that exterior foam insulation makes wall sheathing warmer and dryer. (For example, see the data from the Coquitlam test hut.)

I am not saying, of course, that there are failures in Sweden. The Swedish wall system works fine. But there is no need to make unwarranted aspersions about the REMOTE system, which is extremely robust. It's ironic (and clearly untrue) that you wrote, "The Canadians never had a good solution for the rim joist space," in light of the fact that the Canadians invented PERSIST, and that exterior rigid foam is an excellent way to insulate rim joists.

Apr 12, 2014 5:50 AM ET

by Gregory La Vardera

Martin - I am not making unwarranted aspersions - I am expressing my opinion in the comment section.

And my opinion is that piling foam on the outside of the wall is not an "excellent way to insulate the rim joist". It is an expensive way, and it then triggers a whole host of flashing complications, that again I feel American builders will be unprepared for, and unwilling to invest the time and cos to execute correctly.

Also the performance of Remote style walls in Canada, where very cold temperature ranges are common, and the thickness of foam has to be sized to anticipate this, is a different situation than introducing it in the US where the temperatures are higher, extreme cold spells are becoming more common, and there will be resistance to building beyond code.

That is simply my opinion, that is what I am calling a recipe for failure.

The Swedes invested a great deal in building science and rejected this approach. They did not reject it because their housing industry wants to spend more on walls than they need to. They rejected it because they had better solutions. Today they have a housing industry where every house is built to high performance levels. What do we have in North America?

Apr 12, 2014 5:57 AM ET

Edited Apr 12, 2014 6:03 AM ET.

Response to Gregory La Vardera
by Martin Holladay

You are entitled to your opinions, of course. But the data don't support your opinions.

You wrote, "Also the performance of REMOTE-style walls in Canada, where very cold temperature ranges are common, and the thickness of foam has to be sized to anticipate this, is a different situation than introducing it in the US where the temperatures are higher."

If you are worried that the spread of the REMOTE system from cold climates (Alaska and Canada) to the lower 48 states will leak to an increase in problems, then you have the situation backwards. Designing walls with exterior foam is easier, not harder, in warm climates than in cold climates, because less foam is required to keep the wall sheathing above the dew point in winter.

It looks like I'm in the same boat as Dana (on a different issue). We're just going to have to agree to disagree on this point.

Apr 13, 2014 10:44 AM ET

by Gregory La Vardera

I think I've made myself very clear, but I'll try one more time, and I'll try not to insult you nor suggest you are ignorant. You keep returning to the same claim regarding the performance data which leads me to believe you do not follow what I am saying despite its simplicity, or less generously you are choosing to respond to what you want to and ignore the rest.

First, I know that a Remote wall system will perform fine within its design parameters. And I am aware they can be made more resilient by adding more foam. And I am aware that if BSC builds a test assembly perfectly it will live up to its premise. And yes, they have lots of data supporting that. That is not my point.

My contention is that these wall systems will not be built in the ideal context of a test, they will be built in market place by real people, not scientists, and that best laid plans being what they are they will fail. The data supports my assertion that there is a point at which these Remote walls will fail to perform. You may not agree that these conditions will come about, but it is the simply physics of the matter is that this is true. You know this to be true, and continuously stating that the data does not support my opinion is a deliberate misinterpretation, and disingenuous.

Building Errors: If Remote style walls become widespread contractors will make mistakes when they build these walls. You know this to be true, you are well familiar with the track record of the American housing industry.

Out of range conditions: Changing climate has not and will likely not continue to cooperate with our longstanding categorization of climate zones. We are clearly experiencing wider variations and divergent conditions. You say that warmer climates are easier to design for Remote wall systems. I say that is wrong. In fact current design standards make these walls more vulnerable with the out of range weather conditions we are experiencing. But it does not take climate disaster to experience out of range conditions. All it takes is a teenager who takes 1/2 hour showers.

Economics: The economic incentive for builders is not to build in margins that make these walls more resilient. You know this to be true. The industry has a long history of cutting corners, and in the case of large merchant builder so value engineering home models to extract as much value from assemblies as possible.

These factors combine to create pressures that make these Remote style wall assemblies risky. They are already fragile, and it is my opinion that they will not stand up to the rigor of adoption in the wider housing industry. We have better options.

Apr 13, 2014 10:57 AM ET

Gregory is making some valid points'
by aj builder, Upstate NY Zone 6a

And Gregory I too have voiced exactly your concerns as my own. I have remodeled homes where rigid foam thoughtfully employed over OSB on the exterior caused the worst rot possible. Three times I have found framing that was so far gone as to have become soil no wood left period. Meanwhile the finish layers were there so the customers are standing there so disbelieving that even looking at the damage they think I am somehow involved subterfuge.

We builders should build assemblies that do not fail easily from almost assembling all correctly.

Martin and Dana by the way I also respect the knowledge you both convey here... but Gregory is making some valid points. To me at least.

Apr 13, 2014 1:27 PM ET

I also respect Martin and
by Gregory La Vardera

I also respect Martin and Dana's position. But I believe I am making valid criticisms. If my expression seems exaggerated, its because I see no critical stance with regards to these assemblies.

@aj I think the kind of failures you see are due to exactly the kind of application I am wary of. This was no strict application of the Remote Wall premise. The Remote Wall approach recommends 2/3 of your insulation value outside the sheathing. The stipulations for exterior foam applications without interior vapor control in our code in no way approach this. You can have 2" of foam - R10 over even the worst possible wall assembly - 2x4 w/R11, and you are still not even close to their recommendations.

In the US it is not in the least bit uncommon for a remodeling contractor to apply 1-2" of foam over an existing wall assembly with kraft faced batts. This is all kinds of bad, but many of them think they are following best practices for energy efficiency.

Apr 13, 2014 2:40 PM ET

Gregory, every contractor in
by aj builder, Upstate NY Zone 6a

Gregory, every contractor in my area is making the same "too little foam" mistake over glass filled walls of old.

GBA seems to not understand the realities of the actual majority of the building and remodeling market.

Apr 13, 2014 2:53 PM ET

foam on the outside
by Debra Glauz

I do not understand the benefit of demanding our walls dry to the inside by putting foam on the outside. Not even considering moisture loading of the sheathing in the winter, it would seam if there was a leak from the outside due to inclement weather, the foam wall will be at risk. There will be leaks over the 100 year life of the building. Seems like we will need a fast way to dump water behind the foam. I know there are products for this but why create a problem then have to fix it. I also wonder what the effects of 100 years of paint maintenance will have on the drying to the interior for moisture loading in the winter. Seems like a vapor open system in the form of rockwool board on the exterior combined with a rain screen ventilation channel would be more resilient than a load of foam sheathing on the outside. I just don't understand peoples attraction to exterior foam. Rockwool will warm the sheathing, everything dries, what's not to like.

Apr 13, 2014 3:10 PM ET

Debra, good points, you may
by aj builder, Upstate NY Zone 6a

Debra, good points, you may be predicting where many start to go..... May take decades, people are very very adverse to new and change...

Apr 13, 2014 4:15 PM ET

by Malcolm Taylor

I agree, but there is a large jump that Mr. La Vardera makes from championing mineral wool to his reductionist claim that only his wall works. The variants are numerous: a conventional stud wall with rigid mineral wool batts on the exterior in place of foam, his quickly dismissed double wall with the outer one balloon framed to eliminate thermal bridging. There is more than one way to skin a cat - although I'm reluctant to enter this debate after seeing the abrasive way Mr. La Vardera deals with anyone who disagrees with him.

Apr 14, 2014 6:39 AM ET

Edited Apr 14, 2014 6:41 AM ET.

Response to Gregory La Vardera (Comment #37)
by Martin Holladay

I'll try to find some points of agreement.

You wrote, "First, I know that a REMOTE wall system will perform fine within its design parameters." Good. So we agree on that point.

You wrote, "My contention is that these wall systems will not be built in the ideal context of a test, they will be built in market place by real people, not scientists, and that best laid plans being what they are they will fail."

I think we agree on this point as well: namely, that if a wall system is built right, it will work well, but if errors are made, then it can fail.

Here's the main point, though: if a builder is sloppy, or if a builder doesn't understand water management issues, or if a builder doesn't know how to flash a wall, or if a builder doesn't pay attention to airtightness, almost any type of wall can fail. The need for good workmanship is universal. It applies to REMOTE walls, but it also applies to Swedish walls.

You ask for an apples-to-apples comparison. Fine. Let's compare a well built REMOTE wall to a well built Swedish wall. Fair enough? Both work.

If you want to talk about sloppy practices, we can also compare a poorly built REMOTE wall -- say, one with bad flashing -- to a poorly built Swedish wall -- also with bad flashing. Fair enough? Either wall can fail, of course.

You hypothesize that we should be building well-flashed walls with mineral wool insulation, a carefully installed smart vapor retarder (installed with attention to airtightness), and an interior service cavity. That's a nice wall. Do American framers and insulation contractors know how to put that wall together? Not really, but they can learn. There are ways to teach builders what matters, and how not to screw it up. That takes education. You are trying to educate builders; so am I.

I don't think that I have ever bad-mouthed the Swedish wall. There is no need to bad-mouth REMOTE walls.

Exterior insulation makes sheathing warmer and dryer, and makes a wall assembly less risky. And by the way, exterior insulation doesn't have to be foam. It can be mineral wool -- a fact that GBA has highlighted in many articles.

Apr 14, 2014 7:44 AM ET

by Jayadi Nash

I like working with mineral wool because, unlike fiberglass, it doesn't leave me itchy and scratchy.
Unfortunately, I have been unable to find it since moving to central Florida.

Apr 14, 2014 8:58 AM ET

by Ron Keagle


If the various wall designs all work if built without defects, why does a wall with exterior insulation make sheathing warmer and dryer, and make the wall assembly less risky?

Apr 14, 2014 9:13 AM ET

Edited Apr 14, 2014 9:32 AM ET.

Response to Ron Keagle
by Martin Holladay

Q. "Why does a wall with exterior insulation make sheathing warmer and dryer, and make the wall assembly less risky?"

A. The short answer is "physics."

The longer answer is that the relationship between the temperature of sheathing and its moisture content is a matter of physics, and that researchers have confirmed that sheathing that is protected with exterior insulation (a) stays warmer than sheathing without any exterior insulation and (b) stays dryer than sheathing without any exterior insulation. The method used by the researchers is to insert moisture probes into sheathing and monitor the sheathing moisture content during the winter.

Apr 14, 2014 9:14 AM ET

Edited Apr 14, 2014 9:20 AM ET.

by Terry Lee

I’ve read A LOT of opinions here but little ‘fact’. Is it a ‘fact’ that REMOTE walls with foam are doing fine or, is the fact that they are growing in popularity in the north the “fact” and whether they are ‘doing fine’ or growing in popularity an unknown? If they are doing fine and growing someone please point to the data that shows a life cycle, mean time to failure? Also, please tell me how besides a bunch of hype and theory how I can design a wall and set the dew point to some depth or distance away? Show me air seal data? What thickness what lap joint, what stagger, let’s see some design guides that show the actual dew point location? If this is the answer lest see some ‘facts”? I’m not looking for a bunch of pretty words here and theory, how wood will absorb faster or slower, some code that do not directly apply. I’m looking for some REAL field data or test that shows humidistats and/or other temperature thermocouples, blower door test at build and 30 years later, and a fungi resistance value of foam stacked up in a common wall assemble in all climate zones? I could care less about theory keep it to yourself. I can show that peel and stick at the seams does not have a long thermal life, no adhesive at room temp cure does, try at least 75 psi and 400F clean room cures to get 30 years at best. I’ll give it 10 years at best providing no voids or debri in the bond lines which is VERY unlikely.

Wood is highly unpredictable that is a very well known fact. If someone invented it today it never be approved as a building material. It’s strength properties depend on its orientation, no two pieces are alike, cruelly of all it expands and contracts based on relative humidity, it expands differently based on orientation, when in shrinks it expands, it shrinks and expands along the grain differently than perpendicular, shrinks and expands more at a right angle to the grain than along the grain, studs get shorter or longer, do not get thinner or thicker. It burns, rots, it can’t get worse but, after years of testing and use we understand it to some degree but not entirely. That’s why this industry designs with such high safety margins that fight themselves in weight and dead loads. There are far better material choices, better strength-to-weight ratios, and combinations that work well together, that resist moisture and fungi so get over it.

We know some other facts about manufactured foam, they are Halogenated Flame Retardants (HFRs) - Chlorine and bromine fire retardants(C or BFRs) base produce dioxins, are highly carcinogenic human health hazards when exposed to fire. They are also created in the formulation of PVC and found as chlorinated or brominated fire retardants or (BFRs) to a host of products. There is no required labeling or legislation for quantity of HFRs. OEMs need to be pressured to produce less toxic materials. There are alternative non-flammable materials vs foam and halogen-clad wiring. I’m surprised a ‘green’ site promotes their use. Take a look at what it has done to our ocean and toxic environment. Let’s hope there is ban on its use soon! Don’t use this if you are building air tight, and want a “Indoor Airplus” or pass an IAQ test for Energy Star Certification.

We know some facts about mineral wool, mineral wool forms naturally when strong winds blow through molten lava to create the thin, gold-colored strands that volcanologists call Pele’s hair. Today’s mineral wool insulation is made in a less dramatic process using basalt and iron-ore slag (pre-consumer recycled slag from iron manufacturing) that is melted, spun into fibers, and held together with a phenolic resin. It’s a natural fire resistant. which melts at around 1300°F (704°C). Unfaced mineral wool can withstand temperatures in excess of 2000°F (1093°C) for over five hours with zero smoke developed. Knauf ECOSE technology has Roxul beat since it is formaldehyde free and lower embodied energy.

There is no comparing mineral wool to foam and fiberglass, it wins hands down by material properties not opinion. The Swedish have the answer on configuration, that is a no brainer. If you want some general data look at all the sites with failing western framing and foam on the internet. Many issues with foam, many, many environmental and health related law suits especially lately.

I must say I think Gregory has done a great job here. Even after being referred to as ‘ignorant’ by Marin, & Dana whom ignore his main valid points with a bunch of washed down theory, he held his cool and responded well.

I watched the 4 video series on the Swedish builds, all three walls are better than western. I think we turned for the worse back post industrial revolution when some nit wits decided it was a good idea to integrate studs and utilities with insulation and it has been a failing battle ever since as seen by the ‘ignorant’ trying to make sense and justify a bad design and configuration with foam band aides, simple as the problem is on its face, still some just don’t get it. I think it is great they don’t since it leaves the doors open in this country for the smarter builders to surpass them. Only place for foam is trapped in a sandwich construction where it’s properties can be combined in a monolithic design and toxins or high particles per billion trapped permanently. Even then a bio-based product is better, or better yet a natural product since when it gets down to it you just cannot trust factory manufacturing.

Gregory, the video and pics don’t really detail the lower sill installation well so I will try and get a hold of you. I sent you an email through your site. Thanks, Terry

Apr 14, 2014 9:26 AM ET

Edited Apr 14, 2014 9:28 AM ET.

Response to Terry Lee
by Martin Holladay

Like you, many green builders prefer to avoid the use of rigid foam. GBA has solicited articles for years from builders who have installed mineral wool on the exterior of wall sheathing, and have published several articles on the topic, including the following:

Mineral Wool Boardstock Insulation Gains Ground

Installing Mineral Wool Insulation Over Exterior Wall Sheathing

Installing Roxul Mineral Wool on Exterior Walls

Wrapping an Older House with Rock Wool Insulation

You wrote, "I’m looking for some REAL field data or test that shows humidistats and/or other temperature thermocouples, blower door test at build and 30 years later, and a fungi resistance value of foam stacked up in a common wall assemble in all climate zones?"

Like you, I love research -- especially long-term research. In my opinion, there haven't been enough studies of wall durability spanning 30 years. Such research is expensive, but I welcome it. We've done our best to report on relevant research on these issues.

There has been research on air barrier durability by Canadian researchers. GBA has also reported on several studies of sheathing moisture content; see, for example, this article: Monitoring Moisture Levels in Double-Stud Walls. While this article deals with only one type of wall, GBA looks forward to publishing more research results as they become available.

You wrote, "Please tell me how besides a bunch of hype and theory how I can design a wall and set the dew point to some depth or distance away? ...Let’s see some design guides that show the actual dew point location?"

I suggest that you start with these two GBA articles:

Are Dew-Point Calculations Really Necessary?

Calculating the Minimum Thickness of Rigid Foam Sheathing

Apr 14, 2014 9:30 AM ET

Edited Apr 14, 2014 9:33 AM ET.

Cycle Testing
by Terry Lee

Here is an example of factual test lab data on a seal I am testing that did not make it far. Let's see some similar lab or field data on REMOTE walls? Seals and adhesives any design that relies on them don't last long, better if high pressure and temp and the adhesive is designed for it. You would need to qualify the bond line by ultra-sonic and x-ray test since a void or delamination is an a breading ground for fungui. We do fungi testing too lets see some fungi resistance test of these assemblies too? Say over 30 years?

" Test Facility Comments: Test article started leaking about 68 cycles into the 2nd section of testing at -40 deg. F. Sample leaked about 15 mL in first 10 minutes, then the leakage rate increased to where the leakage had exceeded 75 mL in 20 minutes. See data sheet"

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