# How to insulate block wall around stairs?



## chandler48 (Jun 5, 2017)

You've got a bad situation that will be difficult to insulate. With only 1 1/2" between the cmu and staircase, about all you can do is replicate what the PO had by strapping, XPS and a finished wall.


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## Nealtw (Jun 22, 2017)

How wide are the stairs including stringers?


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## XSleeper (Sep 23, 2007)

When I'm faced with a wall like that I will usually do it in 2 layers. A solid layer of 1/2" foam, with 1/2" x 1 1/2" plywood furring on top of that, anchored to the wall 16" on center, with 14 1/2" rips of 1/2" foam between the furring. Then drywall.

It's unfortunate that the stairs weren't spaced out from the wall in preparation for an eventual 2x4 framed and insulated wall.


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## chandler48 (Jun 5, 2017)

Nealtw said:


> How wide are the stairs including stringers?


According to the tile (if they are 12 x 12, the stairs are 3' or so.


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## chandler48 (Jun 5, 2017)

Brant's idea would work, giving a solid base for the sheetrock and allow the XPS to butt to each other while being taped at the seams. Not much R value, but good thermal break.


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## b.rooster4321 (Apr 22, 2020)

Foam injection into the block while they drill small holes in every core and fill it with foam


Sent from my iPhone using Tapatalk


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## Nealtw (Jun 22, 2017)

chandler48 said:


> According to the tile (if they are 12 x 12, the stairs are 3' or so.


I am living in hope. Well Hope is just 30 miles up the road.
Congoleum® Sensations Sunstone Stone White 14 x 14 Vinyl Tile (20.4 sq.ft/ctn)


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## XSleeper (Sep 23, 2007)

16" cement blocks... 12" tile, the way it looks. You won't be able to finish it according to Ontario strict code on r value.


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## fergie_1977 (Dec 29, 2015)

XSleeper said:


> When I'm faced with a wall like that I will usually do it in 2 layers. A solid layer of 1/2" foam, with 1/2" x 1 1/2" plywood furring on top of that, anchored to the wall 16" on center, with 14 1/2" rips of 1/2" foam between the furring. Then drywall.
> 
> It's unfortunate that the stairs weren't spaced out from the wall in preparation for an eventual 2x4 framed and insulated wall.


This is a great suggestion. I think this will be our best approach. It’s only a small area as the rest of the basement are 2x4 walls front wall is 2x6 (walkout basement).
Yes, the PO misfired when building the stairs and not considering finishing the basement.


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## fergie_1977 (Dec 29, 2015)

Nealtw said:


> How wide are the stairs including stringers?


About 37.5” (outside to outside).


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## fergie_1977 (Dec 29, 2015)

chandler48 said:


> Brant's idea would work, giving a solid base for the sheetrock and allow the XPS to butt to each other while being taped at the seams. Not much R value, but good thermal break.


Would that leave enough room for trim where the drywall meet the stringers?


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## chandler48 (Jun 5, 2017)

Probably not. It would require the sheetrock to be finished well on the bottom and caulked.


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## fergie_1977 (Dec 29, 2015)

XSleeper said:


> 16" cement blocks... 12" tile, the way it looks. You won't be able to finish it according to Ontario strict code on r value.


Oh I totally agree. This is pretty much a ‘make do with the hand we’ve been dealt’ situation. Lol.


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## XSleeper (Sep 23, 2007)

chandler48 said:


> Probably not. It would require the sheetrock to be finished well on the bottom and caulked.


Good place for tearaway L-bead.


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## Nealtw (Jun 22, 2017)

fergie_1977 said:


> About 37.5” (outside to outside).


I would install 1 1/2" foam board and then run the drywall on to the stringer 1 1/2" with a J bead. 
Code is 36" rough or 35" finished.


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## ObserverX2930 (Jan 19, 2021)

I have seen a spray on cork product that would cover the wall and provide "some" insulation.

Contact — Jelinek Cork Group® They are in Canada and also have distributors in the USA.

Mike Holmes used it once over stucco on the outside of a house.

You might want to smooth the block surfaces and level the troweled joints first to have a level surface.

The cork application looked really nice. I think they also do pool surrounding flat surfaces that way. It stays cooler in the sun.


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## fergie_1977 (Dec 29, 2015)

Hi folks, I’m getting ready to tackle this wall now that the new window is in. Question - should I replace the pink insulation that’s stuffed between the block and rim board gap with expanding spray foam? Here’s some pics…


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## chandler48 (Jun 5, 2017)

Yes, absolutely. Compressed fiberglas insulation provides no insulation basically. It must be lofted, so substituting low expanding foam will be a great addition. You may want to poke some of the fiberglas into the block holes as a backer to keep from filling the holes with foam.


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## fergie_1977 (Dec 29, 2015)

chandler48 said:


> Yes, absolutely. Compressed fiberglas insulation provides no insulation basically. It must be lofted, so substituting low expanding foam will be a great addition. You may want to poke some of the fiberglas into the block holes as a backer to keep from filling the holes with foam.


Thanks very much for the reply! Sounds good like a good approach to seal this area up.


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## fergie_1977 (Dec 29, 2015)

chandler48 said:


> Yes, absolutely. Compressed fiberglas insulation provides no insulation basically. It must be lofted, so substituting low expanding foam will be a great addition. You may want to poke some of the fiberglas into the block holes as a backer to keep from filling the holes with foam.


I have a Great Stuff Pro foam gun and a can of window and door foam. Can I use this to fill the void, or should I be using the big gaps and cracks type foam?


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## chandler48 (Jun 5, 2017)

"A" can, probably won't be enough, but it should do the job, and give you more control where the foam goes. I use OSI Quad system, which is similar.


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## DIY Rook (Oct 27, 2021)

fergie_1977 said:


> This is a great suggestion. I think this will be our best approach. It’s only a small area as the rest of the basement are 2x4 walls front wall is 2x6 (walkout basement).
> Yes, the PO misfired when building the stairs and not considering finishing the basement.


Hey Fergie,

what did you end up doing and how did it work?


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## fergie_1977 (Dec 29, 2015)

XSleeper said:


> When I'm faced with a wall like that I will usually do it in 2 layers. A solid layer of 1/2" foam, with 1/2" x 1 1/2" plywood furring on top of that, anchored to the wall 16" on center, with 14 1/2" rips of 1/2" foam between the furring. Then drywall.
> 
> It's unfortunate that the stairs weren't spaced out from the wall in preparation for an eventual 2x4 framed and insulated wall.


Well, I’m finally getting ready to tackle this tricky insulation (took a back seat during extensive main floor and exterior reno’s).
Can I get away with gluing (PL300) the 1/2” xps to the block wall; then gluing the the 1/2” furring strips to the xps without driving screws into block wall; then gluing the second layer of xps between the furring strips; then screw the drywall to the glued furring strips?
Would like to avoid driving any holes in the foundation blocks if I can.
Or am I risking the glue not holding it all to the block wall over time?


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## chandler48 (Jun 5, 2017)

Yes, use PL300 Foamular adhesive. However, 1/2" is only going to give you a thermal break, not much insulation. Furring strips won't hold on XPS for wall construction. I still would build an independent wall along the XPS since you will be needing electrical service in the wall and the 1/2" XPS won't allow that to happen.









LOCTITE PL 300 10 fl. oz. Foamboard Adhesive 1421941 - The Home Depot


Loctite PL 300 Low VOC Foamboard Adhesive is a premium grade formulation specifically designed for bonding foamboard insulation to a variety of surfaces, interior or exterior. Compatible with all other



www.homedepot.com


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## fergie_1977 (Dec 29, 2015)

chandler48 said:


> Yes, use PL300 Foamular adhesive. However, 1/2" is only going to give you a thermal break, not much insulation. Furring strips won't hold on XPS for wall construction. I still would build an independent wall along the XPS since you will be needing electrical service in the wall and the 1/2" XPS won't allow that to happen.
> 
> 
> 
> ...


Thanks for the quick reply. This is that tricky location I have around the basement stairs that I only have the thickness of the stringer to work with for insulation and drywall. Here’s some pics…


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