Insulation of a bowed basement wall
Hi,
Thanks to this site and all the great advice. Climate zone Eastern 6B I would say (summer pretty hot and humid, winter mostly dry and pretty cold (-20 C). One cinder blocks wall in our basement was bowed inward and has been repaired (engineer plan) by putting vertically “L” steel studs 4in x4in every 16″ in front of the wall. But now we’re left with the insulation and that is complicated. If we put polystyrene, it will be tight on the wall in the center but they’ll be a space of 1″ at the top and bottom due to the bulged wall. Also, there are the steel plates on the wall that are 1/4″ thick. Also, there is some cement placed along the steel studs where ever there was a space behind the steel studs, so it is often bumpy around the studs. So, is polystyrene a good idea? How to manage to make it tight? We can’t spray foam because that will lock the humidity inside the blocks and could deteriorate the mortar. And wool or rock wool isn’t really advised directly on a basement wall because it’s not either an air or vapor barrier (so high risk of high humidity within the walls). Any details and opinions would be greatly appreciated, Julie
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>"We can’t spray foam because that will lock the humidity inside the blocks and could deteriorate the mortar."
Huh?
Steel is more moisture tight than spray foam.
Sheet polystyrene is about as moisture-tight as spray foam.
Portland cement mortars only deteriorate if moisture is moving through it, but will last for centuries when wet even saturated with no movement to the moisture. Leaving the blocks open to the indoor air causes ground moisture to come through the wall into the indoor air, taking dissolved minerals with it. The minerals get deposited on the indoor side of the wall as efflorescence when that happens. If you seal the wall the minerals stay in place- no new mineral is being dissolved out of the mortar if there is no replacement moisture coming through the wall.
It's fine to install rigid expanded polysytrene (EPS) the same depth as the steel, then seal over it (and the steel) with an inch or two of closed cell spray polyurethane foam. If rigid board use EPS (usually white, with a visible macroscopic bead structure- the same stuff as beer coolers) not XPS (usually pink blue or green, no bead structure). All XPS in North America is blown with extremely high global warming potential HFC blowing agents, whereas EPS is the same polymer but blown with low-impact pentane, most of which escapes the foam and is recaptured at the factory. As the HFCs slowly diffuse out of the XPS over a few decades it's performance drops to that of EPS of similar density. Once fully depleted the R-value (like that of EPS from day-1) is stable.
Similarly, some closed cell polyurthane is blown with extreme impact HFC245fa, though some are blown with fairly innocuous HFO1234ze (and has a higher performance, usually about R7 @ 25mm/1")
It's also possible to just spray over the steel & block wall with 2.5-3" of HFO blown closed cell foam. If it's continuous at that depth (no steel poking through) it's performance would meet/beat IRC 2018 standards for basement insulation.
Thank you very much Dana. I already knew the difference between XPS and EPS. We won't use spray foam because 1) it's very expensive in our region and 2) I read scientific articles and experts comments about the health safety of spray foam (both types) and it is not convincing and safe so far. Building green is not only about efficiency, for us it's also about indoor air quality.
We never had mold issues before, and this bulged wall was insulated with 2" XPS (R-10), not sealed, and with only a piece of fiberglass wool in front of the rim joist. No mold.
I attach a drawing of the 2 options in front of us : OPTION A: loosing a little more space inside and putting 2 layers of EPS, with air in front. I would put some insulating tape around the tip of the steel studs not covered by EPS. I would like to put a 3rd layer of EPS in the "lost space" (please see drawing) but I don't know how to hold that, because Tapcons are not long enough. The OPTION B: we loosea little bit less space - that is preferred by my husband because our house and basement are not big - but we would put rock wool in front of 1 layer of EPS. The question is how to tighten this rock wool on the EPS. Maybe we would have to buy 2 different thicknesses to accomodate. I would prefer the Option A. What do you think? And do you think it is necessary to seal the top of the hollow cores of the cinder blocks? How? (but this place is difficult to access I have to say).
Keep it inexpensive with EPS. If you do layers of 3/4 to 1" thick it will bend quite radically. I've done round homes by layering it so seams overlap. Slap wet dark paint on irregularities and push the EPS foam against it for a visual impression. I use a multi tool with round blade to contour where high points are on the wall. I would use tapcons or "two nails per hole" with large roofing washers (cheapest) to force it to stay tight to the wall.
thank you very much Paul. I like the details about which tool can help. Would you cover the hollow cores of the cinder blocks at the top of wall? with what ?(the access to that is difficult I have to say).
How much of the block is covered by the bottom plate/mud sill? Guess I would cut foam to fit and use spray foam to fill in. If using a foam gun with canister on top, you have to add tubing to the nozzle tip to reach up and over.
Julie,
The one thing that sucks when insulating around steel studs is that they conduct a lot of heat. Your setup is similar to brick ledge in commercial buildings if you want to google the issue.
If you want the insulation to work, the insulation needs to also cover the steel completely, I'm with Dana on this, 1" to 2" of sprayfoam over everything is the simplest.
You can do a bit of DIY cobble/foam if you want to save money. Basically your option B but skip the roxul (its not going to increase the R value of the wall much) but you need to also get at least 1" of foam onto the steel. The steel angle needs to be completely covered. Probably one of the smaller 2 part foam kits will do you basement and you can use it to also seal your rim joist while you are at it.
Hi Akos,
Interesting.
Why do you say the Roxul won't increase the R value so much? At 4.1 per inch (the AFB Roxul), it' s more then the EPS.
Ok, maybe you'll find that funny but here is an idea, to try to increase the heat around the steel or in order that no condensation happens on that cold surface: before putting the EPS - and maybe the roxul- I could entirely tape the steel studs with this specialized tape: http://www.cantech.com/product/294 (I called the rep, and it'perfect on metal and it's resistant to humidity). Why this idea? During summer in the basement, a lot of condensation was occuring on all the cold water plumbing pipes and water dripping on the floor (no ceiling). We put a round soft foam around the pipes and the problem was solved, we never saw a drop of water after.
This is the problem with steel construction. The cavity insulation has very little effect on the overall R value of the wall. What matter is the insulation outside the steel.
For example a 4" light gauge steel wall with R15 insulation comes in around R6 whole assembly R value. The insulation between the studs doesn't do much. Even if you sprayfoam the whole cavity (R25), the wall R value is something like R8.
With your thick steel angles, this becomes even worse, thus the important part is insulating the steel. Extra insulation in the cavity helps but usually not worth the cost or effort.
They are only 4x4 so I'd use recycled EPS to fill in and either make foam columns or just go the full 4" depth then cover with last 2" over everything. You can get extremely cheap foam from roofing companies after tear off.
Paul I really like your thinking outside the box. If 4" of EPS is put, why put another 2" in front? It seems a lot to me, and it's a Big loss of space (for my husband = huge). If there'll be no mold/humidity issues created by the insulated wall, we're fine. Our 1st criteria is indoor air quality (no mold, no pollutants or less possible) and then, after, energy efficiency. We don't mind heating a little more, or wearing a sweater.
You don't need to go overboard with the insulation but you do need to cover the steel angles completely. The problem is that any exposed steel will be cold and will sweat especially in the winter (water behind the drywall means moldy drywall).
For air quality, the important part is to air sealing. You don't want any air to be able to get behind the foam, air leaks here are a recipe for mold. This is why spray foam over the whole surface is usually the best way to seal these things up.
You can do it with cut and cobble but you have to pay attention because of all the transitions and edges.
Thank you so much Akos. Digesting everything. I have one other challenge. My husband found a good way to insulate with EPS on the cinder block wall and all around the steel studs (will post a future picture for reference). There will be at least 2 1/2" EPS all around the steel studs except in the front where there will be 1" min. We made a prototype and it's incredible how the surface of EPS is warm compare to the steel stud. So I think it works great (but a LOT of work for my husband ahead). On the last row of open cinder blocks, we have decided to tape (with an excellent tape) some Typar to stop air flow that could circulate from the bottom of the cinder blocks to the top. Last problem: The top of the steel studs go up, in front of the rim joist. It doesn't touch the 1st floor - there is an air gap of approx. 3/4 inch between the end of the steel stud and the 1st floor (pic attached). I DON't want to spray air foam (in my area no certified installer, I don't trust at all the spray foam guy , + expensive), and I won't spray foam myself with multiple cannisters either. On the rim joist, we'll put a 2 1/2" EPS and a "sealant-caulking" around it. THE question is: we can't put anything else in the cavity of the rim joists except some optional Roxul but we thought of putting a Typar in front of the rim joist cavity so the air is moving less - so it acts a little bit as a vapor retarder because the air is moving less but it allows a certain drying because there is no vapor barrier. What do you think? As I said, we don't aim for energy efficiency, we aim for no condensation and indoor air quality. We never saw moisture problems in the basement before with only wool in front of the rim joists but the ceiling wasn't done and now we'll make one. But now we have a monster-steed wall. We would appreciate your opinion - and of everybody here. Nothing optimal, but a good way to go to prevent condensation. About the pic: I'm standing on the basement floor and looking up at the rim joist and the 1st floor. We see a cinder block. Thank you tremendously for all your help.
There are some spray applied caulk products:
https://www.greenbuildingadvisor.com/article/air-sealing-with-sprayable-caulk
You can also try to cover things over with some duct seal mastic (basically brush-able caulk that comes in a bucket).
Depending on what your plans are for the foundation on the outside, it might just be simpler to just insulate on the ouside. This would save you having to deal with all these details and you can than just hang drywall straight over the steel angles.
Might not be much more work plus you can remove some of the problematic soil that bowed foundation at the same time.
Thank you SO much Paul. Following your advice, we (husband) created a prototype of foam column with great success (pic attached, it' just a part of the prototype). Please see my other question sent to Akos.
Steel is about 400x as thermally conductive as EPS or rock wool. It doesn't take a large area of exposure on the steel to completely undercut the benefits of only partially insulating over the steel.
If the insulation isn't made air tight there will be convective transfer of moisture between the foundation and basement. With cut'n'cobbled polystyrene between the steel the sealant has to be flexible & durable to stand up to the differing coefficients of expansion/contraction of the dissimilar materials. Spray polyurethane foam is pretty good in that regard.
Thank you very much Dana. I'll make research about a good flexible, durable and compatible sealant. Please see my last question to Akos. Please forget about spray foam anywhere. It's not caprice, we're in the country where the only guy spraying is not certified and doesn't want to mention which spray foam he uses.
Horror... I also discovered that between 2 steel studs, 2 jack posts have been installed to better support the central beam. I've told my husband that without spray foam, he has no choice but to make a footing and move the jack posts outside of the insulated wall, and he's a little discouraged to do that. By any chance, do you know about special posts that wouldn't conduct cold so we could just replace the posts? (1 grey and 1 black on the pic)
One approach to deal with this would be to install exterior grade steel studs that penetrate into the room at the same depth as the flanges on your H-beam steel, and install a continuous layer of 2.5-3" foil faced polyiso on the interior side, leaving the space between the foundation and foam board empty. The polyiso (or perhaps broad sheet polyethylene between the foam & studs) would have to be detailed as an air barrier, but this is more workable than any cut'n'cobbled foam solution. It does take away more interior space however.
If the intent is to finish out the room, going with air-tight steel studs and a continuous 1.5" of foil faced polyiso with a wood 2x3/R8-ish or 2x4/R11-R15 (unfaced or kraft) studwall tight to the foam hits a comparable thermal performance level and make it easier to route the electrical and hang wallboard, etc.
I think Dana has the right idea here with interweaving a steel stud wall to align with the structural steel.
Going off this concept, if you are trying to save inches you could do the following: Set the interwoven studs 1.5" or 2" back from the face of the structural steel and set a piece of polyiso between the structural steel pieces to create a surface flush or just proud. Then follow with the continuous 1" or 1.5" layer of polyiso, finished as an air barrier. You can glue the backside of the seems of the outer layer to the under layer for better air sealing.
Remember all this foam needs a thermal barrier over it, unless using a rated foam like thermax. Drywall can be put up by installing 9/16" cdx strapping on the outside of the foam.
The air seal at the floor and at the mudsill is very important here. This can be done with adhesive type sealants, but one part water cure canned foam is going to be worlds easier. This foam is a more stable chemistry in application than two part foam and lower risk. Scale matters a lot too, when just edge sealing, you are using very little foam compared to using it for bulk insulation.