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6 Helpful?

How to Insulate a Basement Wall

If you want to avoid moisture problems and mold, choose your insulation materials carefully

Posted on Jun 29 2012 by Martin Holladay

Here at GBAGreenBuildingAdvisor.com, we regularly receive questions from readers about the best way to insulate a basement wall. Since these questions pop up frequently, it’s time to pull together as much information as possible on this topic.

In this article, I’ll try to explain everything you always wanted to know about insulating basement walls.

Is it worth insulating a basement wall?

If you live in Climate Zone 3 or anywhere colder, it’s cost-effective and wise to install basement wall insulation. This advice applies to those who live in most of New Mexico and most of Alabama, as well as all of Oklahoma, Arkansas, and South Carolina, and anywhere colder than these states. (Click here to see a climate zone map.)

Canadian researchers who studied basement insulation methods and costs in five Canadian locations (Toronto, Ottawa, Halifax, Edmonton and Victoria) concluded that “for all types and sizes of basements assessed in this study, the lowest total life-cycle cost was associated with basements insulated internally, full-height to a nominal level of R-20.”

How much money will basement insulation save you annually? According to a report published by the U.S. Department of Energy, the annual savings attributable to R-20 basement insulation in a 1,500-square-foot home ranged from $280 per year in Washington, DC to $390 per year in Buffalo, New York, assuming that natural gas costs $0.72/thermUnit of heat equal to 100,000 British thermal units (Btus); commonly used for natural gas.. (However, energy consultant Michael Blasnik cites two Minnesota studies that show lower levels of savings. See his 6/29/12 comments posted below.)

What do building codes require?

The 2012 International Residential Code requires basement insulation in Climate Zones 3 and higher. Here are the minimum code requirements for basement wall insulation — assuming that you are insulating with foam, not fiberglass batts:

  • Climate Zone 3: R-5
  • Climate Zone 4 (except Marine Zone 4): R-10
  • Marine Zone 4 and Climate Zones 5, 6, 7, and 8: R-15.

Should I insulate the wall on the inside or the outside?

I used to believe that the best location for basement wall insulation was on the exterior. In recent years, however, I’ve decided that interior basement insulation makes a lot of sense.

However, there are valid reasons for both approaches, and either way can work fine. So if you prefer one approach, don’t hesitate to use it.

Here are the advantages of exterior basement insulation:

  • Exterior insulation keeps the concrete within the home’s thermal envelope; this increases the amount of interior thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. and reduces the likelihood of temperature swings if heating and cooling equipment stops working. (However, it’s worth pointing out that the advantages of interior thermal mass are often exaggerated.)
  • Exterior insulation protects the dampproofing or waterproofing layer from damage during backfilling.
  • Insulating on the exterior allows a builder to install an uninterrupted layer of rigid foam from the foundation footing to the rafters. While this approach isn’t required — you don’t have to insulate above-grade walls with exterior foam if you don’t want to — many builders like it.
  • Exterior insulation provides more interior space in your basement than interior insulation.
  • It’s easier to insulate and air-seal the rim joist area with exterior insulation than with interior insulation.
  • If you insulate on the exterior, you avoid the expense of interior studs and drywall.
  • Exterior insulation leaves the interior of the concrete wall exposed (assuming the basement is unfinished) so that the concrete can be inspected at any time for cracks.

Here are the advantages of interior basement insulation:

  • The insulation work integrates more smoothly with the construction schedule, since it happens after the building is dried in rather than when the excavation contractor is eager to backfill the foundation.
  • It’s easier to provide an uninterrupted connection between the below-slab insulation and the wall insulation when the insulation is on the interior. If you install the wall insulation on the exterior, the footing will usually interrupt insulation continuity. (For more information on this issue, see Foam Under Footings.)
  • If you insulate on the interior, you avoid the hassle of figuring out how to protect the above-grade portion of the exterior basement insulation.
  • If you plan to install brick veneer on your above-grade walls, interior basement insulation makes more sense than exterior insulation. (For more information on the incompatibility of brick veneer with exterior basement insulation, see Image #4, below.)

Briefly, how are basement walls insulated on the exterior?

After the basement wall has been protected with a dampproofing or a waterproofing system, insulation is installed from the top of the footing to somewhere near the top of the rim joist. Acceptable insulation materials include extruded polystyrene (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.), expanded polystyrene (EPS), closed-cell spray polyurethane foam, or mineral wool. Polyisocyanurate insulation should not be used because it can absorb water.

Below-grade insulation does not need to be attached to the concrete; it is held in place by the backfill. The best backfill material is a fast-draining granular material like gravel or crushed stone with a thin cap of soil or clay.

Above-grade insulation may or may not need to be attached to the concrete — fastening methods include foam-compatible adhesive, TapCons with washers, and specialty fasteners like Hilti IDP fasteners or Rodenhouse Plasti-Grip PMF fasteners — depending on the height of the exposed foam and the method used to protect it.

Some builders cantilever their 2x6 perimeter walls so that the basement insulation isn't proud of the siding. If the basement insulation ends up proud of the siding, you'll have to protect the top of the basement insulation with metal flashing. The top of the flashing needs to include a vertical leg that extends upward and is lapped by the housewrap; the flashing should be sloped, and the bottom of the flashing needs to terminate in a drip leg that extends beyond the insulation and the insulation protection materials.

If I insulate on the outside, how should I protect the above-grade foam?

The above-grade portions of all types of exterior insulation must be protected from physical abuse and sunlight. Among the products than can be used for this purpose are the following:

For more information on this topic, see How to Finish Exterior Foundation Insulation.

Briefly, how are basement walls insulated on the interior?

The best way to insulate a basement wall on the interior is with foam insulation that is adhered or attached directly to the concrete. Any of the following insulation materials are acceptable for this purpose: closed-cell spray polyurethane foam, XPS, EPS, or polyisocyanurate.

Rigid foam can be adhered to concrete with foam-compatible adhesive or can be attached with special fasteners like Hilti IDP fasteners or Rodenhouse Plasti-Grip PMF fasteners. (For more information on using Hilti IDP fasteners to attach rigid foam to a basement wall, see Marc Rosenbaum’s article, Basement Insulation — Part 2. For more information on Rodenhouse Plasti-Grip PMF fasteners, see New Green Building Products — June 2013.) To prevent interior air from reaching the cold concrete, make sure to seal the perimeter of each piece of rigid foam with adhesive, caulk, a high-quality European tape, or canned spray foam.

Building codes require most types of foam insulation to be protected by a layer of gypsum drywall. Many builders put up a 2x4 wall on the interior of the foam insulation; the studs provide a convenient wiring chase and make drywall installation simple. (If you frame up a 2x4 wall, don't forget to install fire blocking at the top of the wall. For more information on fire blocking, see Fire-Blocking Basics.)

One brand of rigid foam, Dow Thermax polyisocyanurate, meets code requirements for a thermal barrier and can therefore be left exposed in a crawl space (and in some jurisdictions, in a basement) without the need for a layer of gypsum drywall. If your basement doesn’t need wiring, studs, and drywall, then Thermax is probably the brand of insulation to use. (However, be sure to check with your local building official before going this route.)

If you plan to insulate your basement walls with spray foam, the best approach is to frame your 2x4 walls before the foam is sprayed, leaving a gap of 1 to 2 inches between the back of the studs and the concrete wall. The gap will later be filled with spray foam.

For information on insulating rim joists, see Insulating Rim Joists.

If you live in an area where termites are a problem, your local building code may require that you leave a 3-inch-high "inspection strip" of bare concrete near the top of your basement wall. To find out what details are required in your area, talk to your local building official.

Can I insulate on the interior with fiberglass batts, mineral wool batts, or cellulose?

No. Fiberglass batts, mineral wool batts, and cellulose are air-permeable. When this type of insulation is installed in contact with concrete, the moisture in the interior air condenses against the cold concrete surface, leading to mold and rot. That’s why I advise builders that fiberglass batts, mineral wool insulation, and cellulose should never be installed against a basement wall.

The risk of moisture problems is reduced if the concrete is first covered with a continuous layer of rigid foam or closed-cell spray foam. If that is done, some builders then install a 2x4 wall on the interior side of the foam insulation and fill the stud bays with fiberglass batts. This approach is less risky than installing fiberglass directly against the concrete. However, I don’t think that fiberglass batts belong in a basement. My advice: if you want a higher R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. , just install thicker rigid foam, and leave the stud bays empty.

Does interior basement insulation need to be vapor-permeable?

No. The idea that a damp concrete wall should be able to dry towards the interior — in other words, that any insulation on the interior of a basement wall should be vapor-permeable — is mistaken. In fact, you don’t want to encourage any moisture to enter your home. Your concrete wall can stay damp for a century; that dampness won’t hurt the concrete.

For more information on this topic, see Joe Lstiburek Discusses Basement Insulation and Vapor Retarders.

Should I include a polyethylene vapor barrier?

No. Basement wall systems should never include any polyethylene. You don’t want poly between the concrete and the insulation; nor do you want poly between gypsum drywall and the insulation. You don’t want poly anywhere.

Paul Ellringer, an energy and mold consultant in Saint Paul, Minnesota, has a collection of slides showing moldy basement insulation. In most cases, these basement walls were insulated with fiberglass batts, and included two layers of polyethylene — one on each side of the studs. Ellringer calls this a “diaper wall,” and reports that most of them are a mess. “Fibrous insulation and poly are inherently problematic, and should not be used in below-grade walls,” says Ellringer. “Sometimes when you open it up, the fiberglass is soaking wet. If the house is two to four years old, the studs are often beginning to rot.”

What about ICFs or the ThermoMass system?

If you build a new basement with insulated concrete forms (ICFs) or the ThermoMass system, your wall already includes insulation, so you don’t need to add any more.

Both approaches work. The main disadvantage of these systems is their high cost compared to conventional poured concrete walls.

ICFs have a core of concrete sandwiched between two layers of rigid foam. ThermoMass walls have a core of rigid foam sandwiched between two layers of concrete. It seems to me that the ThermoMass sandwich makes much more sense than the ICF sandwich: since foam is more fragile than concrete, it makes more sense to protect the fragile layer with concrete than to put the fragile material on the outside of the sandwich.

If you decide to use either ICFs or the ThermoMass system, pay close attention to the wall’s R-value. Many ICF and ThermoMass walls have relatively low R-values. If you’re going to buy such an expensive wall system, be sure to specify thick foam.

What do I need to know if I am installing insulation on an existing house?

If you want to insulate an existing basement, you’ll probably be working from the interior. Before installing a layer of foam insulation on an existing wall, the first step is to verify that the basement wall doesn’t have a water-entry problem.

Diagnosing and fixing water-entry problems in existing basements is a big topic in its own right, and is beyond the scope of this article. Suffice it to say that if your basement walls get wet every spring or every time you get a heavy rain, the walls should not be insulated until the water-entry problem is solved.

Among the possible solutions to this problem:

  • Adjusting the grade around your house so that the soil slopes away from the building on all four sides;
  • Installing roof gutters connected to conductor pipes that convey the roof water away from the foundation;
  • Excavating the exterior of your foundation and installing new footing drains leading to daylight;
  • Installing an interior French drain around the perimeter of your basement and connecting the drain to a sump equipped with a sump pump; and
  • Installing a layer of dimple mat against the basement walls before insulating.

For more information on these issues, see Fixing a Wet Basement.

If your basement has stone-and-mortar walls, you can’t insulate the walls with rigid foam. The only type of insulation that makes sense for stone-and-mortar walls is closed-cell spray polyurethane foam.

If your basement has poured concrete or concrete-block walls, you can proceed with the same methods used for new construction — as long as you’re sure that the walls don’t have a water-entry problem.

What about crawl space walls?

Crawl space walls should be insulated with the same methods used for basement walls. For more information on insulating a sealed crawl space, see Building an Unvented Crawl Space.

Basement wall insulation is a cost-effective measure

Remember: if you live in Climate Zone 3 or anywhere colder, installing basement wall insulation is almost always cost-effective. Performing this work will lower your energy bills, and will also provide an important side benefit: insulated walls are less susceptible to condensation and mold.

That means that insulated basements stay dryer and smell better than uninsulated basements.

Last week’s blog: “Understanding Energy Units.”

Click here to follow Martin Holladay on Twitter.


Tags: , , , , , , ,

Image Credits:

  1. Fine Homebuilding
  2. Thermomass
  3. Building Science Corporation
  4. Journal of Light Construction

101.
Mar 25, 2014 8:49 AM ET

Response to Matt M
by Martin Holladay

Matt,
Most of the steps you suggest are sound.

1. You can leave the Typar in place if you want. It isn't doing any good, but it isn't doing any harm. You should know that Typar and Tyvek are both vapor-permeable in both directions, so it won't really stop water vapor transmission.

2. You could try to convince your local inspector that the proposed XPS is already a vapor retarder / vapor barrier. If the inspector won't listen to logic, then I guess you will have to buy the MemBrain.


102.
Apr 5, 2014 6:35 AM ET

Zone3,Georgia, ? Basement wall insulation
by Nat Hilton

Hello Martin,

Thanks for your time and efforts. Very informative website.
I am currently trying to finish my walkout basement. However, I already have studs up, 2x4, electrical and plumbing ran. My issue here is how do I insulate this basement. I bought the house 4 months ago, and have not seen any water issues, slight condensation on windows though.
I cannot afford spray foam, I only have about 1 1/2 behind studs.
1. Should I try to put 1" rigid foam xps behind stud, seal, tape as much as I can, then fiberglass, then drywall?
2. If I fit in 2" bwtn studs, seal as much as I can with greatstuff? If I do this, being that 2" has a r-10, do I even need to use fiberglass? Now this is all against concrete walls.
3. How do it insulate the non-concrete walls ,( the walkout side) if I decide to go with either method? Is it the same as nonconcrete walls. It's already studded.
Now while changing insulation at rim joist, the area in the basement under the stairs, there are some rotted plywood. I can see the brick of stairs. Apparently I was told no flashing was use. Some repair to the stairs was made not too long ago, it seems. How can this situation be rectify? I have someone coming out to check it out, but I just want to ask the right questions.
Also it's been hard to find 1" inch pink stuff or dow in my local area. But HD sells 3/4 inch of owens corning rigidfoam sheathing. Can I use this stuff indoors? I guess the difference is the plastic on it to protect against the elements. I don't have time to order online.

Thanks again, Natasha


103.
Apr 7, 2014 8:52 AM ET

Edited Apr 7, 2014 8:54 AM ET.

Response to Nat (Natasha) Hilton
by Martin Holladay

Natasha,
If I understand correctly, someone has framed 2x4 walls near your concrete foundation walls, leaving a gap of 1 1/2 inch between the concrete and the 2x4s. Is that right?

If that's correct, then the best way to insulate these walls is with closed-cell spray polyurethane foam. The installer should take care to make sure that the space between the concrete and the studs is completely filled.

If you can't afford to do that, you can try to slide 1 1/2-inch-thick XPS insulation between the concrete and the studs. This job needs to be done in an airtight manner. It's going to be awkward -- much more difficult than spray foam. Every seam in the XPS needs to be carefully sealed with canned spray foam or high quality tape.

After that work is done, I suppose that you can install rigid foam between the studs using the cut-and-cobble method if you want. I'm not a fan of cut-and-cobble, but you can do it. Again, spray foam would be easier. For more information on the cut-and-cobble method, see Cut-and-Cobble Insulation.

Q. "How do it insulate the non-concrete walls ( the walkout side) if I decide to go with either method?"

A. Just as you would any other above-grade wall. Whatever method you choose, pay attention to air sealing.

Q. "Now while changing insulation at the rim joist, the area in the basement under the stairs, there are some areas of rotted plywood. I can see the brick of stairs. Apparently I was told no flashing was used. Some repair to the stairs was made not too long ago, it seems. How can this situation be rectified?"

A. I don't know if you are talking about interior stairs leading to the basement or exterior brick stairs leading to your front door. In any case, it's impossible to diagnose this problem from your description. This problem requires a site visit. If you have rotten sheathing, a rotten rim joist, or missing flashing, you may have to do extensive repair work.


104.
Apr 7, 2014 11:53 AM ET

If I understand correctly,
by Nat Hilton

If I understand correctly, someone has framed 2x4 walls near your concrete foundation walls, leaving a gap of 1 1/2 inch between the concrete and the 2x4s. Is that right?

Yes, that is correct.

If you can't afford to do that, you can try to slide 1 1/2-inch-thick XPS insulation between the concrete and the studs. This job needs to be done in an airtight manner. It's going to be awkward -- much more difficult than spray foam. Every seam in the XPS needs to be carefully sealed with canned spray foam or high quality tape.

No, I cannot afford spray foam. I can only buy the 3/4 or 2" pink rigid foam board locally. If I want 1" or 1 1/2 " I have to order and I'm pressed for time.

After that work is done, I suppose that you can install rigid foam between the studs using the cut-and-cobble method if you want. I'm not a fan of cut-and-cobble, but you can do it. Again, spray foam would be easier. For more information on the cut-and-cobble method, see Cut-and-Cobble Insulation.

So, are u suggesting, foam behind the stud, then foam, bwtn stud, thus eliminating the need for fiberglass? Also, the 3/4 " is actually a sheathing (protective film on both sides) usually use for exterior purposes and not a board. Does this matter?

I might be going the gobble gobble method... Lol. I meant the cut and gobble. My son and I could easily do this.

So should I do the thin foam then fiberglass, or avoid fiberglass at all cost and just do rigid foam "pancake" style?

I'm in georgia, zone 3.

Thank you so much.


105.
Apr 7, 2014 12:03 PM ET

Edited Apr 7, 2014 12:05 PM ET.

Response to Nat (Natasha) Hilton
by Martin Holladay

Natasha,
Q. "Are you suggesting, foam behind the studs, then foam between studs, thus eliminating the need for fiberglass?"

A. No. I am suggesting closed-cell spray polyurethane foam, but you don't want to do what I suggest. When it comes to fiberglass, I thought that my article -- the article that is on the same page that you are now posting a comment on -- was clear on that point. I wrote: "Can I insulate on the interior with fiberglass batts, mineral wool batts, or cellulose? No ... I don’t think that fiberglass batts belong in a basement. My advice: if you want a higher R-value, just install thicker rigid foam, and leave the stud bays empty."


106.
Apr 7, 2014 3:01 PM ET

Ok, thank you very much.
by Nat Hilton

Ok, thank you very much. Apologize for the confusion. I will be putting in a rigid foam behind the studs, then do the cut and gobble behind (2") rigid foam bwtn the studs. I will be sealing with great stuff gap and crack . Then sealing with a tyvek tape bwtn seams. No fiberglass!!;)
My ceiling already had fiberglass insulation. What are your suggestions on that?

The rotted rim joist is just below front stairs. Looks like at one time prev owners did some work on front stairs. Funny thing is my inspector suggested before purchase for prev owner to seal around stairs. One would think he would have gone in basement and check to see if there were any water damage. I've only been in the house 3 months and this was old rot. Well we had a good bit of rain last night and today, and I had someone to come check it out. Yep, water is seeping in. So, they will be replacing plywood with pressure treated plywood...etc..

Anyway, your forum was a God sent... Many thanks..
(Back to the basement now)


107.
Apr 7, 2014 3:07 PM ET

Roxul sound insulation
by Nat Hilton

I'm thinking off putting in roxul sound batts in interior wall to help with noise control, and possibly some resilient channel on ceiling to help with noise control. Any thoughts on that?

And I believe I just ask another question on basement flooring? Would tiling then area rug be the best option?


108.
Apr 7, 2014 3:32 PM ET

Response to Nat (Natasha) Hilton
by Martin Holladay

Natasha,
It's best to post comments that are relevant to the article where you are posting. Since your most recent questions aren't about basement wall insulation, you should post your questions on GBA's question and answer page. Here is the link:
http://www.greenbuildingadvisor.com/qa


109.
Apr 7, 2014 4:34 PM ET

Alrighty, thanks again..
by Nat Hilton

Alrighty, thanks again..


110.
Apr 15, 2014 11:11 AM ET

Edited Apr 15, 2014 11:41 AM ET.

leave space between fiberglass insulation and concrete wall
by Fred Zheng

I live in West Chester, PA. I just received three quotes about finishing my 1700 sq ft walk-out basement. All three of them plan to insulate the wall with fiberglass batts between the frames and leave a 1.5-3 inch space between the insulation and the poured concrete wall. One contractor will also install a little computer fan in that space to keep the air circulating. When I told them about the idea of using rigid foam board, I was told that they have never done it, it's unnecessary and too expensive. From what I read so far, I understood that fiberglass batt should not be installed directly against the concrete wall. Could you please explain why it's also not good enough by leaving a space between the fiberglass batts and the concrete wall? Forgot to mention, I painted the concrete wall with dry-lock 2 yrs ago so my kids have a cleaner basement to play before I have it finished. Does the dry-lock paint provide some benefit or actually will cause problem now when to finish the basement? Thanks.


111.
Apr 15, 2014 11:28 AM ET

Response to Fred Zheng
by Martin Holladay

Fred,
Q. "I just received three quotes about finishing my basement. All three of them plan to insulate the wall with fiberglass batts... When I told them about the idea of using rigid foam board, I was told that they have never done it."

A. Walk away from these contractors and keep looking until you find a contractor who understands building science principles.

Q. "Could you please explain why it's also not good enough by leaving a space between the fiberglass batts and the concrete wall?"

A. The concrete wall is cold. The indoor air in your basement is warm and humid. The fiberglass insulation is air-permeable, so it doesn't prevent warm interior air from contacting the cold concrete. The usual result of this type of insulation job is that (under the right conditions) condensation forms on the concrete wall, drips down to the floor, and form puddles near the bottom plate.


112.
Apr 15, 2014 11:48 AM ET

Thanks. A further complication regarding dry-lock paint
by Fred Zheng

Forgot to mention, I painted the concrete wall with dry-lock 2 yrs ago so my kids have a cleaner basement to play before I have it finished. Does the dry-lock paint provide some benefit or actually will cause problem now when to finish the basement? such as using rigid foam against the paint? The curious thing is that one contractor wants to put two-coats of dry-lock on the wall and one coat of oil-based dry-lock on the concrete slab floor. Thanks.


113.
Apr 15, 2014 11:58 AM ET

Edited Apr 15, 2014 11:59 AM ET.

Response to Fred Zheng
by Martin Holladay

Fred,
Q. "Does the DryLok paint provide some benefit?"

A. Yes. It can limit moisture flow through the concrete.

Q. "Will the DryLok cause problems now when to finish the basement?"

A. No.

For more information on DryLok, see Fixing a Wet Basement.


114.
Apr 23, 2014 8:33 AM ET

Basement Wall Insulation
by Shawn CURRIE

All I can say is, "wow" to all the articles and information on this site. I was a drywall contractor for the last 10 years in Ontario, Canada. I thought I knew a little about insulation. This blog has got me wondering.
The way basement walls are done up here (and nearly 90% of houses up here have them); 2 X 4 framed wall with tar paper backing (stapled to back of studs), no space between the back of studs and block wall, R12 fiberglass (blown or batt), then sealed with 6 mill poly and acoustic caulk. This is minimum code.

Everything I read on here is suggesting this is not a good process? Am I reading all this right?


115.
Apr 23, 2014 9:37 AM ET

Response to Shawn Currie
by Martin Holladay

Shawn,
Q. "Everything I read on here is suggesting this method [fiberglass insulation with interior polyethylene] is not a good process. Am I reading all this right?"

A. Yes, you are reading this right. Building codes in much of Canada (and in many areas of the U.S.) are about 20 years behind the times when it comes to building science knowledge. Remember, just because a house meets code, doesn't mean it's well built.


116.
Apr 23, 2014 12:11 PM ET

The reason I stumbled upon
by Shawn CURRIE

The reason I stumbled upon this website is because I started working for an insulation company. I wanted to know the building science behind the R Value myths, dew points and thermal bridging to help me educate potential clients.
Everything on here contradicts what we do. Right up to using polyethylene on the interior of a building when we are using rigid foam board on the exterior, osb and fibeglass in the cavity. Most contractors know it's wrong, but inspectors tell them it has to be done.
Here's my next question; if we have studies to show the effects of improper building practice, why is it taking 20 years to put them into place?
This is all very new to me, so forgive my ignorance.


117.
Apr 23, 2014 12:47 PM ET

Response to Shawn Currie
by Martin Holladay

Shawn,
Local jurisdictions usually adopt a version of a model code, like one of the codes developed by the International Code Council.

The process to introduce an amendment to one of these codes is cumbersome, taking a minimum of three years. Lobbyists have to support these changes. That's expensive, and such work is usually supported by a group with a financial interest. It may take 2 or 3 code cycles (6 or 9 years) for a proposed amendment to be adopted.

After an amendment is approved, the new code is only a piece of paper until it is adopted by a local government. If adopted, it is often first amended. This process can take 2 or 20 years.

A few links:

http://mwalliance.org/sites/default/files/uploads/MEEA_2010_Midwest%20En...

http://www.iccsafe.org/gr/Documents/AdoptionToolkit/toolkit.pdf

http://www.aamanet.org/upload/file/Codes_GM0512.pdf

http://pffacts.blogspot.com/2013/09/home-builders-slow-dysfunctional.html


118.
Aug 15, 2014 12:52 PM ET

Edited Aug 15, 2014 1:01 PM ET.

The R-20 recommendation
by Nick Welch

Martin, I think I've found a flaw with your mention of the Canadian study that found R-20 to be most cost-effective.

Their R-20 was achieved using 5 1/2" batts. They compared it against XPS with R-10 and EPS with R-9 and both of those were more expensive to install and saved less energy than the batts.

I do agree with you that batts are a bad idea for moisture reasons, so the question that leaves us with is, how much foam is really most cost effective? Your article basically reads like this: "R-20 is most cost effective... foam is best... so, use R-20 foam". But the cost of R-20 foam may actually be an extravagance that doesn't make sense for a lot of people.

On the other hand, a DIY installation will have no labor cost, so thicker foam may have a chance to pay itself back within the 30 years used in that study.


119.
Sep 21, 2014 9:33 PM ET

Edited Sep 21, 2014 9:34 PM ET.

Re-insulating an already finished basement
by corey hansen

Hello Martin,
Thanks for this informative article. I'm just reading it today though it was posted two years ago.

We live in Wisconsin (zone 6) so winters are cold and summers can be humid--the dehumidifier runs all summer currently.
Some facts about the basement are:
1. Some will be playroom space, some will just be storage. Those areas are separated by doors.
2. We had all of the rim joist area spray foamed this summer all the way around the edge of the basement.
3. The existing finished space walls have a combination of furring strips and white styrofoam. There is also electrical with shallow boxes along the walls. We want to keep electrical in the space.
I have attached a photo of this.
4. Ceilings are 7-7'6", so not really deep for insulating the floor.
5. The basement is dry. We have a dehumidifier that still runs, so hopefully if we do something it will help with that (saving money for electric bill).

My questions are these:
1. Is it better to insulate some of the wall, like the two foundation walls of the finished playroom space (the other two are interior stud walls) if I can't do all of it all the way around the basement, or is it an all/nothing proposition in terms of humidity, insulation, etc.?
2. I want to put carpet on part of the floor of the playroom area. Any advice on that?
3. How would I seal the gap between the spray foam in the rim joist and any rigid foam I put on the wall (I did not think to put up the pink foam before having the rim sprayed. Would it work to run a bead of Great Stuff along the top of the pink foam?
4. How thick should the interior rigid foam be for zone 6 code -- 1"? 2"?
5. Can I adhere the foam to the concrete with Great Stuff or foam adhesive if I don't want to hammer drill it? Would it work if it wasn't adhered at all and the studs kept it in place?
6. Your advice is to leave stud cavities empty if there is rigid foam behind them, right?
7. What if I end up just putting drywall back up (it was paneling), do nothing with rigid foam and call it good enough if it's cost/time prohibitive to put foam in based on your advice? Our budget is small after foaming the basement and doing some other reinsulating through a contractor.

Thanks for any advice.
Corey Hansen


120.
Sep 22, 2014 3:33 AM ET

Response to Corey Hansen
by Martin Holladay

Corey,
Q. "Is it better to insulate some of the wall, like the two foundation walls of the finished playroom space (the other two are interior stud walls) if I can't do all of it all the way around the basement?"

A. Yes.

Q. "Or is it an all/nothing proposition in terms of humidity, insulation, etc.?"

A. No.

Q. "I want to put carpet on part of the floor of the playroom area. Any advice on that?"

A. Carpet cannot be installed on a basement slab unless there is a layer of rigid foam under or over the slab -- especially in a basement that is so humid that it requires a dehumidifier every summer. In the summer, humid air will condense on the cold slab under the carpet, leading to mold. Either install tile flooring or vinyl flooring, or install a layer of rigid foam, followed by OSB or plywood subflooring and carpet.

Q. "How would I seal the gap between the spray foam in the rim joist and any rigid foam I put on the wall (I did not think to put up the pink foam before having the rim sprayed. Would it work to run a bead of Great Stuff along the top of the pink foam?"

A. Yes, canned spray foam will work there.

Q. "How thick should the interior rigid foam be for zone 6 code -- 1 inch? 2 inches?"

A. According to the 2009 IRC, a basement wall needs at least R-10 insulation when foam is used in Zone 6. That means 2 inches of XPS or 2.5 inches of EPS.

Q. "Can I adhere the foam to the concrete with Great Stuff or foam adhesive if I don't want to hammer drill it?"

A. Yes. Use a foam-compatible adhesive or an adequate amount of canned spray foam.

Q. "Would it work if it wasn't adhered at all and the studs kept it in place?"

A. Yes, although it's important in that case to tape the foam seams to make sure that the installation is as airtight as possible.

Q. "Your advice is to leave stud cavities empty if there is rigid foam behind them, right?"

A. Yes.

Q. "What if I end up just putting drywall back up (it was paneling), do nothing with rigid foam and call it good enough if it's cost/time prohibitive to put foam in based on your advice?"

A. You will live to regret your decision. Doing this work will never be easier than it is now.


121.
Nov 25, 2014 4:36 PM ET

Exterior Basement Rigid Foam Attached Garage Detail
by Adam Peterson

I would like to insulate my new construction house including the basement with 4" of XPS rigid foam on the exterior side. How would I handle the attached garage in this scenario? Would the basement foundation be poured, then insulated on exterior, then garage slab poured?


122.
Feb 17, 2015 2:31 PM ET

Edited Feb 17, 2015 2:32 PM ET.

ADA for basement stud wall?
by Mark Fredericks

Is it necessary to install the drywall in the airtight approach, when going over a stud wall (with batts) that has rigid foam behind it, up against the concrete? Image #2 in this article is the type of basement wall assembly I'm working with. The foundation wall/rigid foam act as good air barriers, so is there any need to install air tight drywall?


123.
Feb 17, 2015 3:06 PM ET

Response to Mark Fredericks
by Martin Holladay

Q. "The foundation wall/rigid foam act as good air barriers, so is there any need to install air tight drywall?"

A. No, as long as the seams between the rigid foam sheets (and the perimeter of the rigid foam) have been properly air-sealed with high-quality tape, canned spray foam, or caulk.


124.
Feb 17, 2015 3:17 PM ET

Do the batts become less effective?
by Mark Fredericks

Thanks Martin, I'm working with foam that is sealed and pretty tight so I'm not worried about interior air reaching the concrete. I was curious if the effectiveness of the batt insulation would be reduced by allowing interior air to flow into the batts around electric boxes or through un-taped drywall seams. (I should have mentioned that I might not be taping the drywall immediately)


125.
Mar 25, 2015 3:39 PM ET

3" reclaimed fiber Polyiso faced in a Zone 5, confusion reigns
by Darren Finch

So Ive been waiting until Spring starts and the roofing contractors start ripping out old roofs and start to sell the reclaimed Poly on Craigslist.

Ive been planning to do this for the past 18 mths but want to pull the trigger now as the basement finishing now looks like a go (man cave finally)

Anyway Ive been speaking with Insulation Depot and they can do 3" 4x8 poly fiber faced for $21 a sheet, but the more Ive searched through GBA the more confused Ive become for two reasons.

The exterior of my basement is sealed with rubber membrane so water wont be an issue but the vapor internally on the cold concrete in winter is my concern.

So the plan was to glue it directly to the walls, tape sealing the seams and foam the bottom then put up a 2x4 stud wall, giving me an airproof seal
But then with the vapor going through the fiber/board, meeting the cold winter wall, encouraging condensation and mold, Ive seen on various sites, and the same people on those boards saying Poly but it had to be foil faced or XPS.

Ok so foil faced, is that the way I have to go, and then there is the "which way does the foil face" question Im scratching my head over as well.

So let me know 1. can I use the fiber poly on the basement wall or does it have to be foil faced and 2. if Im going foil poly which was does the foil face, to the wall or to the room?

Thank you


126.
Mar 25, 2015 4:20 PM ET

Response to Darren Finch
by Martin Holladay

Darren,
1. Don't worry about vapor diffusion; just worry about airtightness.

2. Either kind of polyiso will work.

3. If you decide to use foil-faced polyiso, the foil can face any direction you want -- but if you face it toward the interior, and leave the stud bays uninsulated, the foil facing + air space will give you a little boost in the wall's R-value.


127.
May 4, 2015 4:36 AM ET

Girder pocket/basement foam
by Caleb Creaven

I am considering insulating the basement of my upcoming northern VT project with foam on the interior and have a concern. (or three). I was going to drop the main girder into pockets in the concrete wall at each end to be able to run the floor I-joists continuously above it but this seems to be a spot where air could leak through and condense on the cold concrete and damage the girder over time. Any thoughts?


128.
May 4, 2015 5:27 AM ET

Response to Caleb Creaven
by Martin Holladay

Caleb,
If it's not too late, it's best if you don't install your beam in a beam pocket. With interior insulation, the beam pocket will stay cold and damp, and these conditions can eventually lead to rot at the end of the beam.

Beam pockets work best on foundations with exterior insulation.

If you plan to install interior insulation, you should support your beam on posts (columns) that bear on concrete footings.


129.
May 4, 2015 7:38 AM ET

Nope, not quite too late!
by Caleb Creaven

I would rather put the foam on the outside to keep the foundation warm and avoid frosty, wet concrete but I want to put 3 inches of EPS on and I don't love the flashing details necessary to cover the top. I'm doing a double-stud wall, albeit with some trepidation after reading the latest updates, so I don't want to cantilever the deck out over the foam. Anyway, decisions, decisions... thanks for your feedback.


130.
Aug 21, 2015 12:18 PM ET

Edited Aug 21, 2015 12:22 PM ET.

EPS or XPS damp basement
by Celeste Schmartin

I have quite enjoyed the Building Science articles about insulating old basements. I live in Zone 2 Saskatchewan, 1940s concrete basement with high seasonal water table (sump pump) and some wall weeping. A few years ago I insulated part of my basements walls with 2" XPS as recommended and am now in a position to do the remainder plus under a new partial slab. In light of the News story #2 in this article and the skyrocketing price of XPS, and articles like the 2013 one on thermal insulation below grade on Construction Specifier, would EPS not be an adequate choice? I have also read that EPS is the go-to rigid foam in Europe, because it is "greener". Thoughts? Thanks.


131.
Aug 21, 2015 12:33 PM ET

Response to Celeste Schmartin
by Martin Holladay

Celeste,
Indeed, most green builders prefer EPS to XPS, because EPS has a benign blowing agent, while XPS has a blowing agent with a high global warming potential.


132.
Sep 15, 2015 12:19 PM ET

Walkout basement interior insulation
by Joshua Fahey

Thanks for this great blog! VERY informative!

I live in a split level home with a walkout basement in Minnesota. The house is built into a slope, so the basement wall facing the backyard is completely above grade. The rest of basement walls are half cinder block. I plan on using XPS against the block, then 2x4 with drywall. My plan was to use batting in the 2x4 cavities in order to achieve greater warmth in the winter (whoever installed the duct work did a poor job), but I'm discouraged from doing that after reading your article. Would I benefit by layering XPS board? For example, if I used multiple layers of XPS board against the block to achieve a 4 + inch layer of XPS, would I achieve a higher R value? Are there any negative of doing this, such as allowing moisture to build between layers of XPS?

Also, the home is 20 years old and there are 2x4 walls that sit on top of the block. The block is slightly jutted out on the interior, creating an approximate 2 inch "shelf." As far as I can tell, there is a thin piece of flimsy white foam (approx. 1/8" thick) between the top of the block and the wooden sill on which the 2x4 framing sits. There does not appear to be any mold issues on the sill, but the block is damp. I plan on putting XPS against the interior side of the block and on the top part of the block that juts out, butting the XPS up to the wooden sill. I am wondering how I should seal the joint where the top piece of XPS and the wooden sill meet. I will be unable to replace the sill without disassembling the whole house. Also, I'm pretty sure I won't be able to wedge any type of vapor barrier or insulation between the top of the block and the wooden sill.

I attached a picture so you can see what I'm dealing with.

IMG_2240.JPG IMG_2241.JPG


133.
Sep 15, 2015 1:10 PM ET

Response to Joshua Fahey
by Martin Holladay

Joshua,
Q. "Would I benefit by layering XPS board? For example, if I used multiple layers of XPS board against the block to achieve a 4 + inch layer of XPS, would I achieve a higher R value?"

A. Yes, you can install two or more layers of XPS. For example, 4 inches of XPS has twice the R-value of 2 inches of XPS.

Q. "Are there any negatives of doing this, such as allowing moisture to build between layers of XPS?"

A. No. There are no negatives. Thicker foam is better than thinner foam.

Q. "As far as I can tell, there is a thin piece of flimsy white foam (approx. 1/8" thick) between the top of the block and the wooden sill on which the 2x4 framing sits."

A. The thin white foam is called "sill seal."

Q. "I plan on putting XPS against the interior side of the block and on the top part of the block that juts out, butting the XPS up to the wooden sill. I am wondering how I should seal the joint where the top piece of XPS and the wooden sill meet."

A. Caulk will work just fine.


134.
Oct 27, 2015 10:41 AM ET

Insulating irregular walls and around a sewer pipe
by Charles Chen

Martin,

I am impressed that you've continued to comment on this thread and provide valuable feedback to the community.

I came across this post in researching how to insulate around my basement after tearing out an existing wall assembly that was riddled with mold on the backside of the wall and in the insulation.

My challenge now is that the wall is stepped with a sloped transition ledge where the two block sizes meet and a large cast iron sewage pipe spanning 3/5ths of the walls in the basement. In some cases, I will have no space or less than 1/4" space for insulation (e.g. around the collars of the pipe).

Additionally, I will not be able to get adequate insulation behind the water heater and build a wall assembly in front of the insulation.

The original wall assembly around the pipe was built 8" off of the concrete wall with paper-faced fiberglass insulation installed in the stud bays. Of all of the walls that I tore down, this is the only wall that did not experience discolored insulation and mold on the backside of the drywall.

I've since had an interior french drain installed with a dimple mat extending 4" up the wall.

I have been considering -- that given the circumstances of this wall and pipe -- it would perhaps be a better idea to get a thicker, continuous layer of rigid insulation installed against the exterior-facing side of the frame assembly glued and taped and leave an air gap between the wall assembly and the concrete. If I install it against the backside of the framing, I could use full, uncut sheets and minimize the number of joints and this would effectively prevent conditioned, moist air from moving through the wall assembly into the air gap.

So working our way in, it would be:

- Concrete block
- Air gap
- 2" XPS foam board, glued and taped
- Steel or wood studs; empty bays
- Mold resistant drywall

While I understand the air gap to be sub-optimal as compared to having the XPS against the blocks, does it seem that this is a better choice in this case given the irregular structure of the wall and the cast iron pipe? This would seem to also be the best option around the mechanicals where I would not be able to build a full wall assembly behind the water heater and air handler so instead, build around it 2" XPS directly attached to the wall assembly.

The contractor that installed the French drain also recommended laying PE VB directly against the concrete, tucked into the dimple mat at the floor. I think that this would be one way of keeping vapor out of the building entirely. The above grade portion of the foundation is anywhere from 8"-24" around the perimeter of the house so I think that there would be adequate surface area to allow the concrete to dry outwards.

I would love to hear some feedback on the above.

0traO.jpg Adhal.jpg


135.
Oct 27, 2015 10:53 AM ET

Response to Charles Chen
by Martin Holladay

Charles,
First of all, pipes and water heaters are not like mountains, established by God and unmovable. Pipes and water heaters can be moved. If you aren't a plumber, you can hire a plumber to move your pipe and your water heater away from the wall.

That said, it may be that you don't want to incur the expense required to move the pipe and the water heater.

Your plan will work, but I urge you to pay close attention to airtightness at every step of the way. Since you will end up with a cold masonry wall, any moisture that reaches that will will condense.


136.
Dec 20, 2015 4:20 PM ET

insulating from the interior
by Michael Lutkenhouse

Martin,

If we insulate from the interior using an EPS system with built in studs is no fire blocking required? or must there be fire blocking at the top?

Further, if XPS is put up against the wall to create the thermal break followed the 2x4 wall, must there be a fire break on top of the XPS? I'm assuming using a thicker 2x would accomplish this.

If there are any easier ways to meet the fire code on the XPS/EPS it would be much appreciated but I'm unclear on how the fire break code applies to foam area's as most of the code seems to refer combustible walls and/or around 2x4's.

Thank you!


137.
Dec 21, 2015 6:13 AM ET

Response to Michael Lutkenhouse
by Martin Holladay

Michael,
My understanding is that fire blocking requirements apply to air pathways or stud cavities -- so if your wall has no air pathways or stud cavities, I don't think that the requirements apply. However, I am not a code official. The only interpretation that matters (in your case) is the interpretation of your local code official -- so call up your local building office and ask.

The article includes an image (Image #5, reproduced below) showing a location where fire blocking is required. For more information, see this article: Fire-Blocking Basics.

.

Fire blocking - basement wall - JLC.jpg


138.
Jan 20, 2016 11:53 AM ET

heavily insulating basement wall
by Sharon Secrist

Our basement has concrete walls and is uninsulated. We would like to add a foot of insulation on the interior.

I understand that mineral wool should not be in direct contact with the wall.

The idea is to insulate with:

1)3 inches (two layers, 1.5 inch each) of expanded polystyrene in contact with the concrete
2)9 inches of mineral wool built out with wood 2x4s and furring strips, covering the foam to the interior
3)plywood or cement board finish

It seems the mineral wool, instead of foam, would allow the wood to dry to the interior if they become wet.


139.
Jan 20, 2016 12:15 PM ET

Sharon- what climate zone ?
by Dana Dorsett

You're putting R12-ish foam on the exterior side of R36-ish rock wool, for a total R of R-48-ish, or about 25% of the total R being air-impermeable foam.

If you're on the cool edge of US climate zone 5 or colder a ratio of 25% is not sufficient for dew point control on the above-grade portion of the walls, and it would be prone to wintertime moisture accumulation (even frost formation) in rock wool on the upper part of the wall.

The interior side sheathing also be tight to the rock wool, with no intermediate air gaps/channels. If it's plywood it doesn't need to be painted, but if fiber cement it eitehr needs to have latex paint to bring it's vapor permeance into Class-III vapor retardency territory, or a smart vapor retarder between the fiber-cement and the rock wool.


140.
Jan 21, 2016 9:40 AM ET

thanks Dana
by Sharon Secrist

Thank you Dana.

Just to be clear, this would all be interior insulation.

I thought I understood the dew point risk when there is a mix of exterior and interior insulation.

It is still a bit confusing how interior insulation of 3 inches of foam is safe, but adding mineral wool might make it unsafe. It seems the air which traveled through the mineral wool would be closer in temperature to the air of the foam, and thus less likely to form frost, than if there were no mineral wool.


141.
Jan 21, 2016 9:57 AM ET

Response to Sharon Secrist
by Martin Holladay

Sharon,
Q. "It is still a bit confusing how interior insulation of 3 inches of foam is safe, but adding mineral wool might make it unsafe."

A. Without any mineral wool, the interior face of the rigid foam will be at the temperature of the interior air (or close to it). In winter, the concrete wall will be cold, while the interior air will be warm. If the interior face of the rigid foam is warm, you won't get condensation on the foam.

If you add a thick layer of mineral wool on the interior side of the rigid foam, then the mineral wool insulates the rigid foam -- separating the rigid foam from the warm indoor air. The mineral wool keeps the foam cooler. With enough mineral wool, it's possible to cool the rigid foam below the dew point. Once you do that, you can get condensation on the interior face of the rigid foam.


142.
Jan 31, 2016 12:08 PM ET

Roxul vs Rigid Foam
by Jason R

I'm getting so many conflicting views and suggestions with how to insulate my basement. I don't have water issues, but I do get some moisture down there (who doesn't). When i moved in I installed a Sante Fe dehumidifer that keeps the whole space under 40% humidity.

I have one exterior wall and section of my basement that will stay unfinished (mechanical area) and then one adjacent wall that will be left unfinished the full length so workers can get to my electrical panel, plumbing pipes and main line etc (about 3 feet wide from the interior framed wall. These 2 exterior walls i'm recommended to have R15 Roxul comfortabatts pinned directly to the concrete and left as is without any type of barriers or anything. For the interior wall that will be up against the conditioned space i'm told to use Roxul safe and sound. Is this suitable for the unfinished space that won't have any drywall? This area will not be cooled or heated, but is where my dehumidifier is located (it will also be duct into the the finished area). Is this acceptable or should I use Rigid Foam board just left as is in the unfinished sections?

The other 2 exterior walls will be up against the interior conditioned space is. This is where I get into so many conflicting views..

One guy suggests that I use the same 3" roxul (R15) AFB and pin it against the concrete (not the roxul comfortboards, then have my contractor frame the walls, (no insulation in between the frame sections) then just drywall and a primer that will act as the vapor barrier. This doesn't seem to be advised at all here, is this proposed idea acceptable to avoid moisture and mold issues? Or should I use rigid foam against the concrete, then have the frame built, then either add roxul insulation or left empty, then drywall with primer and paint?

I'm in NY so I think R15 is more then enough for the finished space. Please help! - Appreciate it!


143.
Apr 20, 2016 3:02 PM ET

A bit confused...
by Greg Volland

Hi guys,

I’m starting the transition of my “crawl” space into living space. My home is fairly new construction and the lot is sloped from back (higher) to front (lower). The portion of my crawl that I want to convert to usable space is roughly 8’2 from the 4 inch slab I had poured (got ahead of myself doing that as I only have crushed rock + poly + 4 inches of concrete and didn’t think to put down foam before the pour).

My foundation walls (8 inches thick) range in height from 18 inches to 48 inches high with 2x6 stud (pony walls ranging from about 48 inches high to 79 inches high) on the foundation wall to the joists of the first floor. I am planning to frame full height walls inset from the concrete walls by a 3-4 inches.
I am in Seattle (Marine Climate 4 I believe) and the exterior of the foundation has no insulation.

My questions:
1) Should I bother to insulate the cavities in the existing 2x6 pony walls? If so, are fiberglass batts ok in this above grade cavity?

2) Should I use rigid foam (EPS or XPS) to cover the 18-48 inch high exposed concrete foundation walls?

a. I assume the answer is ‘yes’ so do I insulate the small parts of the tops of the concrete foundation walls that are not covered by the sill plates (8 inch thick concrete with pt 2x6 in top of it)?

3) I was planning to insulate the interior 2x4 walls I want to frame. Is it a good idea? What is best to use? I had planned to use faced fiberglass batts then sheetrock to finish.

Thank you in advance for helping me do it right the first time!

Greg


144.
Apr 20, 2016 4:27 PM ET

Response to Greg Volland
by Martin Holladay

Greg,
Q. "Should I bother to insulate the cavities in the existing 2x6 pony walls?"

A. Yes. Insulation is a code requirement.

Q. "If so, are fiberglass batts ok in this above grade cavity?"

A. Barely OK. Fiberglass batts are the worst-performing insulation material sold in the U.S.

Q. "Should I use rigid foam (EPS or XPS) to cover the 18-48 inch high exposed concrete foundation walls?"

A. That would work, as my article explains.

Q. "I assume the answer is ‘yes,’ so do I insulate the small parts of the tops of the concrete foundation walls that are not covered by the sill plates (8 inch thick concrete with pt 2x6 in top of it)?"

A. Yes. You will need to install horizontal pieces of rigid foam, at least as thick as the vertical rigid foam installed on the interior side of the walls, to cover these concrete shelves.

Q. "I was planning to insulate the interior 2x4 walls I want to frame. Is it a good idea? What is best to use? I had planned to use faced fiberglass batts, then sheetrock to finish."

A. Again, fiberglass batts are OK. If the framed 2x4 walls are on the interior side of concrete walls, make sure that there is an adequate thickness of rigid foam between the concrete walls and the 2x4 studs.


145.
Apr 20, 2016 5:24 PM ET

Reply to Martin Holladay
by Greg Volland

I was trying to replicate your plan posted here: http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/7-steps-energ... ---- I couldn't tell if I was to insulate both the cavity of the 2x6 pony wall AND the full height interior 2x4 walls that I will frame out.

If I do the closed-cell spray foam, do I still apply the rigid foam board first or just spray to achieve at least the needed R-15 value in my area?

I am looking at DIY spray foam kits. Have you ever heard anything about Foam It Green kits? https://www.sprayfoamkit.com/spray-foam-insulation/products.html?gclid=C...

Thanks for sharing all your wisdom!

Greg


146.
Apr 21, 2016 4:41 AM ET

Response to Greg Volland
by Martin Holladay

Greg,
As I explained in my article, I don't like to install fiberglass batts in basements. Some builders do, however. If you choose to install fiberglass batts in a basement wall, make sure that you have a layer of rigid foam between the studs and the concrete wall, and make sure that the concrete is dry.

Q. "I couldn't tell if I was to insulate both the cavity of the 2x6 pony wall AND the full height interior 2x4 walls that I will frame out."

A. It's up to you to decide the R-value of your insulation. In Climate 4C, the 2012 IRC requires a minimum of R-15 for basement walls (assuming that we are talking about continuous rigid foam or spray foam insulation -- the best approach). That's a minimum R-value; you can install more insulation than that if you want to. Building science principles dictate that a thicker layer of fluffy insulation (if you insist on including fluffy insulation) requires a thicker layer of rigid foam or spray foam insulation. When in doubt, remember that thicker rigid foam or spray foam insulation moves your wall in the direction of less risk, while thicker fluffy insulation moves your wall in the direction of more risk. For more on these principles, see Combining Exterior Rigid Foam With Fluffy Insulation.

Q. "If I do the closed-cell spray foam, do I still apply the rigid foam board first or just spray to achieve at least the needed R-15 value in my area?"

a. It's possible to use 100% closed-cell spray foam if you want, as my article explains. If you go this route, make sure to leave a gap of between 1 and 2 inches between the studs and the concrete, and make sure that the spray foam installer fills this gap with closed-cell spray foam.

Q. "Have you ever heard anything about Foam It Green kits?"

A. I'm not familiar with those kits, but I see no reason why you shouldn't use that brand if you want to. I don't think that the word "green" in this context has anything to do with the environment, however. Here's how the web site defines "green": it says, "Our Signature Green Formula (Green means go - no mistakes, no waste)."


147.
Apr 21, 2016 1:20 PM ET

Reply to Martin Holladay
by Greg Volland

Thanks Martin.

I read the link you posted about combining rigid and fluffy insulation and am confused. The article discusses rigid foam on the EXTERIOR. That is not my planned application. My home's exterior is already complete (OSB + black felt + cement siding) that the builder put on. I am looking to do all my basement/over-height crawl work inside that envelope. Does make any difference?

Also, can I apply closed cell spray foam directly onto rigid foam to get the R values I want and seal up the 'shelf' at the top of the concrete wall as you put it and the rim joist areas or is it 'better' to just end up with a thicker coat of closed cell spray foam (i.e. multiple passes as per the instructions) and not do the rigid at all?

Originally, I was planning to do something along the lines of the attached example that I found on your site.

Greg

hot-mixed-basement-insulation.jpg


148.
Apr 21, 2016 1:34 PM ET

Edited Apr 21, 2016 1:36 PM ET.

Response to Greg Volland
by Martin Holladay

Greg,
When you are combining an air-impermeable layer of foam insulation on the cold side of the assembly with an air-permeable layer of insulation on the warm side of the assembly, there is risk of moisture accumulation if the foam layer is too thin (or the fluffy layer is too thick).

That is the principle discussed in the article I linked to (Combining Exterior Rigid Foam With Fluffy Insulation). The physics is the same -- whether the foam layer is on the exterior side of wall insulation, or whether the foam layer is on the interior side of a cold concrete wall. That said, the concrete isn't at the outdoor air temperature -- at least the bottom of the wall isn't. But the top of the wall may be.

I could discuss the similarities and differences between these different types of wall assemblies if needed, but such a discussion is probably unnecessary -- especially if you want to use just one type of insulation (closed-cell spray foam).

You have many options. It's up to you to choose on option.

100% closed-cell spray foam works.

100% rigid foam works.

A combination of rigid foam and closed-cell spray foam works.

A combination of rigid foam and fiberglass batts works -- as long as the rigid foam is thick enough, and the fiberglass is thin enough. If you want to go this route, tell us what R-values you have in mind for the various layers, and I'll give you a thumbs up or thumbs down.


149.
Apr 21, 2016 2:36 PM ET

Edited Apr 21, 2016 6:51 PM ET.

Response to Greg Volland re Foam It Green
by Dean McCracken

Edited - original comment was based on misunderstanding the proposed usage of foam kits.

I've used spray foam kits to seal/insulate rim joist with great success. In almost every circumstance it is cost-prohibitive to use foam kits in a high-volume project. Regardless, be sure the installed foam is properly protected to ensure fire safety. Fully review the relevant code requirements and manufacturer specifications.


150.
Apr 21, 2016 3:37 PM ET

Edited Apr 21, 2016 3:38 PM ET.

Reply to Martin Holladay
by Greg Volland

Thank you again Martin!

Note: I have already insulated the 2x6 wall cavities that are on top of the foundation wall with R-19 faced fiberglass batts (I did this before I found your website!)

Here is my plan:

Option 1)
1. Adhere 1 inch R-Tech (R value 3.85) or 1 ½ (R value 5.78) EPS Rigid Foam to the interior of the concrete foundation walls (ranging in height from 18 to 48 inches – see pic).

2. Spray 2 inch coat of closed cell spray foam at top of EPS board to cover exposed top portion of concrete foundation wall.

3. Spray interior side of EPS board with 1 inch layer of closed cell spray foam (per Foam it Green, 1 inch thick = R-7).

4. Use rigid EPS + Foam combination to seal rim joists.

5. Build full-height 2x4 walls approximately 2 inches off existing foundation & pony walls, using PT bottom plate and sill seal.

6. If needed: Insulate 2x4 walls with fiberglass roll/batts (thinking R-13 / Faced)

Option 2)

1. Spray 3 inch coat of closed cell spray foam to cover all exposed concrete foundation walls, including the exposed top portion of concrete foundation wall as well as rim joist cavities.

2. Build full-height 2x4 walls approximately 2 inches off existing foundation & pony walls, using PT bottom plate and sill seal.

3. If needed: Insulate 2x4 walls with fiberglass roll/batts (thinking R-13 / Faced)

Thoughts?

Greg

Greg Volland photo 2.jpg


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