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Insulating exterior walls constructed of brick, block, and concrete can be daunting. Most building science professionals suggest that the insulation be located on the exterior of the structure. This helps thermal performance and can improve moisture management if the details are carefully planned and implemented. Building Science Corp. has a great article on the topic called Deep-Dish Retrofits. That being said, there can be challenges associated with that strategy, such as maintaining the historical façade of older structures and zoning requirements for setbacks, a potential issue when a building’s exterior size grows from added exterior insulation.
Insulating these same walls on the interior includes more risk due to moisture issues; after all, most structures built from brick, concrete masonry units (CMU), and poured concrete work on storage and redistribution principles for their moisture management. They get wet, and the moisture is absorbed into the wall, where it is redistributed across the wall assembly and then released (either inward or outward) when conditions allow. This can be problematic if the moisture cannot move into the structure (trapped by some sort of vapor retarder) or when wet walls are subjected to freezing temperatures.
Another challenge is how to insulate CMU and poured-wall basements. This topic happens to be one of the most commonly asked questions here on Green Building Advisor. Martin Holladay has written several good blog posts on the topic:
How to Insulate a Basement Wall – GreenBuildingAdvisor
Three Ways to Insulate a Basement Wall – GreenBuildingAdvisor
Vapor Retarders for Basements and Crawlspaces – GreenBuildingAdvisor
The main takeaways from these articles:
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13 Comments
Now let’s see if they can actually supply this….
Read my mind...
This is a game-changer for me. I always design basement and crawlspace on the interior when possible but have only been comfortable using foam, which I otherwise avoid. Trying to get a perfect variable permeance membrane installation over mineral wool is challenging. This makes me much more comfortable with using mineral wool insulation in basements and crawlspaces.
Looks interesting, but pricing, availability, etc. will obviously be important.
I do think it's hard to beat Insofast (https://www.insofast.com) for finishing the inside of exterior basement walls.
Insofast panels have their place but they need to be covered for fire protection in most cases and they are made of foam plastic, which many people focusing on "green" building try to avoid. For unfinished, conditioned basements, having insulation that needs no additional covering is a benefit.
Michael,
I was under the impression that EPS had less embodied carbon than comfortboard, is that incorrect? Or are you using another criteria for environmental impact? Honest question.
They are in roughly the same category when it comes to embodied emissions; it varies by manufacturer. Other reasons to avoid foam are to limit support of petrochemical companies, avoid potentially harmful ingredients such as biocides in foam, and for mineral wool's far better resistance to fire and the nasty smoke that foam emits when burning. (The chemicals are mostly similar to those in burning wood but that's not healthy either.) I prefer to use lower-carbon materials than either of those but it's not always possible.
I'm not completely comfortable with the use of any fiber insulation on the interior foundation walls, even with the Intello layer. Here in northern VT, our ground temperatures are still near 50F, though they will rise to 55F-60F by midsummer. If you have interior basement at 70F and 50% RH, that air has a dewpoint very close to 50F. So even at the beginning of June, we still have vapor drive from inside to outside and any trapped moisture still won't be drying our. Worse yet, the RH inside the insulation cavity will be close to 100% throughout the insulation profile. This high internal RH would put the Intello into Class III mode, allowing even more vapor to enter.
Also consider the case of above-grade foundation walls with this product in winter. The outdoor temperature is near or below 10F for several months. Pretty much any reasonable interior air conditions have dewpoints well above that. Being a fibrous insulation, there is some amount of vertical distribution of liquid water and vapor as well as lateral. And even with low permeance, there will still be *some* vapor flow through the Intello. Initially, that little bit of moisture will condense on the above grade foundation walls. When enough accumulates, it begins to run down the wall to the bottom, raising the RH of the air within the insulation and "opening" the pores of the insulation. This allows more moisture in, not out, and the process continues and accelerates over time.
Of course this is all dynamic and based critically on air, water and vapor flows. And it's entirely possible that the amount of water that accumulates in a few months is insignificant. It is also possible that the smart people at Rockwool and Intello have already considered this and that everything is OK. Seems like a great opportunity for some grad student to work on their modeling chops.
Peter,
This confuses me a bit too. If we could safely just use rockwool with Intello on the interior side, why wasn't that recommended in the articles Randy has linked to? What has changed now we have a product where one is bonded to the other?
It's pretty difficult to detail Intello over fluffy insulation, so I'm not surprised we don't see it in any articles. Bonding Intello to Comfortboard does make sense, if the physics works out. And my concern really only applies to cold climates. This may be one of the products that makes sense in warmer zones, probably at least Zone 1-4, maybe 5. Everything gets tougher in 6 and 7 with much less drying weather.
I'm an American living in France. The most common (I'm not saying the best) residential wall construction system here is concrete block with an insulated gypsum board panel on the interior. I've attached a photo of one using GPS. EPS is also used. These are readily available even in the big box outlets. I've wondered for a while we they haven't made their way to the USA yet. They seem especially practical for a basement if you're alright with a foam insulation. And as mentioned above GPS and EPS beat mineral wool for GWP.
Conduited wiring is attached directly to the block wall and there's enough of a gap behind the insulation to allow for it. I've also seen people groove the panel backs to allow for plumbing supply lines to be installed against the block as well.
Hello jollygreenshortguy,
Can you please state the name of "insulated gypsum board" products available in France?
Thanks,
Dbliss
#12 The stuff in most of the stores is basically generic. Lots of companies make it. But the biggest name is Saint Gobain. I believe they own Certainteed. They have a product called "Placomur". They come in a range of insulation thicknesses and plasterboard types. Here's a link to one.
https://www.placo.fr/Produits/isolation-des-murs-par-linterieur/placomur-065-1320
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