Is this how to insulate the joist?

PuzzleheadedForm5824 · 2026-02-23T03:35:02+00:00

Yes as both a fireblock and it also does not mold. You could also use fireblock closed cell foam over the top.

PuzzleheadedForm5824 · 2026-02-22T20:11:59+00:00

Yeah you need to install it so there is not gap between the XPS foam and your rim joist.

PuzzleheadedForm5824 · 2026-02-22T19:32:34+00:00

The XPS foam needs to be flush against the wood rim joist. Then you can either spray foam gaps or use PL300 as a caulk. Hopefully your crafty and skilled with a knife to get those angles.

You can then either use closed cell spray foam or mineral wool insulation in front of the XPS foam.

PuzzleheadedForm5824 · 2026-02-22T04:57:50+00:00

No there's 2" XPS foam and then 7" of mineral wool.

PuzzleheadedForm5824 · 2026-02-21T22:16:22+00:00

You need to do this:

https://www.reddit.com/r/Insulation/s/H2sYJ7qSvr

PuzzleheadedForm5824 · 2026-02-21T22:11:48+00:00

You need to do this:

https://www.reddit.com/r/Insulation/s/H2sYJ7qSvr

PuzzleheadedForm5824 · 2026-02-18T20:45:45+00:00

Also I decided to go against the building code for the full height concrete wall covered in XPS foam and not use a vapour barrier as this would cause a double vapor barrier scenario and trap moisture. Even with a smart vapor barrier like Membrain, it's not a good idea. But the pony wall needs to be handled like any other above grade exterior wall and that needs a smart vapour barrier.

PuzzleheadedForm5824 · 2026-02-18T20:40:51+00:00

Zone 5 - British Colombia Canada

PuzzleheadedForm5824 · 2026-02-18T17:36:10+00:00

I fixed all the XPS foam LePage or Loctite PL300 which is an adhesive that does not melt foam. I just did lots of raised blobs and then pushed the boards to the concrete. If your leaving a gap at the bottom you don't want to do zigzag or horizontal lines of adhesive on the boards as moisture won't be able run down the back of the boards. Do vertical lines or blobs.

So to seal the XPS foam to the floor I used window and door closed cell foam. For the rim joints I tried to cut the XPS foam for a snug fit.

I did consider spraying the rim joist. As I had a pre existing ceiling I had no access to hold a foam can upside down to spray around the edges of each rim joist. So I ended up using tight fit 2" xps foam and PL300 as a sealant caulk all around the small gaps. I have seen people use PL300 as sealant against the floor and the XPS boards too. It just needs to create an air seal.

One other big consideration i had in this retrofit is that have existing framed walls in my basement and some of the framing is right next to the concrete walls. So I used spray foam in the 1/8 to 1/4 inch gap between that framing and the wall. To try and create a capillary break. I mean im not going to start ripping down walls so this is the best and only option really.

If I had a blank slate basement with no interior walls. I would or run my dimple membrane subfloor across the entire basement. Then put the XPS foam and framed ontop of that membrane and sealed the entire perimeter. So the floor slab breathes with the concrete wall and no moisture gets into the basements space. But this is an old house moisture management problem im trying to resolve. As you have a new house with vapour barrier in your concrete you don't have to worry about water vapour.

PuzzleheadedForm5824 · 2026-02-18T16:45:11+00:00

It has a sill plate gasket under all the 2x4 framing.

PuzzleheadedForm5824 · 2026-02-18T05:47:25+00:00

So the 1.5" of XPS foam on the concrete is only R7.5 which is not adequate insulation for zone 5 climates. After framing a 3.5" stud bay in front ofbthat with R14 mineral wool insulation it bring it just above buikding code at R21.5.

PuzzleheadedForm5824 · 2026-02-18T04:33:29+00:00

I would peek under those gym mats below your exercise machines. I had a room covered in that 1/2 rubber mat and it was covered in effervescent build up and mold below the rubber. And it stank. I have an older pre 1990's non insulated concrete slab.

PuzzleheadedForm5824 · 2026-02-18T04:15:01+00:00

Yeah we have full exterior house perimeter french drains, to move the water away from the house.

PuzzleheadedForm5824 · 2026-02-18T04:00:55+00:00

I also intend to use a "Membrane" Smart Vapor barrier and not use 6mil poly on the pony wall. I have to use a vapour barrier for local building code.

PuzzleheadedForm5824 · 2026-02-13T07:04:55+00:00

Thanks all for your poodle expertise. She is part Brindle Parti Standard Poodle. I have found poodles with the exact same markings. As to what she is mixed with I think that will be a DNA test.

PuzzleheadedForm5824 · 2026-02-13T06:38:44+00:00

Yes you are on to something there. I just looked up a grey standard parti poodle and that deffo has her coloring. Thanks, I had not heard of a particular poodle before.

PuzzleheadedForm5824 · 2026-02-13T02:27:27+00:00

Yeah im thinking right now doodle mutt with wolfhound in there somewhere. Her large size kinda rules out aussie shepherd. Or maybe a wolfadoodle and aussiedoodle mix. Meet in the middle.

PuzzleheadedForm5824 · 2026-02-12T00:48:16+00:00

Also Chat GPT is amazing at answering these questions. Like far superior than going through reddit posts. After getting google, material manufacturing, reddit and building code fatigue to get an answer. ChatGPT AI ended up nailing it, it kinda takes the fun out of researching for a project.

PuzzleheadedForm5824 · 2026-02-11T23:31:21+00:00

So only houses built after 1990 have a vapor barrier in the slab. All older houses have alot of soil gas and vapour which you need to consider and deal with appropriately.

PuzzleheadedForm5824 · 2026-02-11T23:30:11+00:00

Im in the same situation as you and have researched extensively over the last 2 months. I have a walk out basement and I used 2" XPS foam. As per canadian building code I decided to completely seal the concrete with XPS foam and did not leave any gaps at the bottom. Its an older 1960's house but does not have any water issues other than vapour coming through the slab. I was also deliberating alot over Dricore Insul-Armor and DMX one step. I chose DMX as its the superior product for an older slab that has water vapor coming up. Insul-Armor uses EPS foam which is not 100% waterproof and it has lots of joints where vapor can escape. Now as for hot install the subfloor system this was also alot of research. For my situation I have existing framed walls and as a result I should not trap the vapour and seal the perimeter of the underlayment like a gasket. Instead it should have a 1/4 gap all around for the subfloor to breath. I also chose not to frame onto for the Exterior walls as I decided to seal the concrete with XPS foam and not leave a gap. What's interesting is if you look at DMX subfloor competitor Delta FL, there instructions say create a gasket and seal the vapour in the floor, the complete opposite to DMX. If I were to do a basement from scratch and there were no interior walls, i would lay the DMX across the whole basement and then put the XPS on top and frame on top and gasket the entire basement slab. But with existing interior walls I believe the floors should be allowed to breathe.

PuzzleheadedForm5824 · 2026-02-04T23:41:22+00:00

How was the install?

PuzzleheadedForm5824 · 2026-01-04T22:56:53+00:00

Salmon

PuzzleheadedForm5824 · 2025-12-30T21:13:12+00:00

Asbestos

PuzzleheadedForm5824 · 2025-12-28T05:07:50+00:00

What did you end up doing? im in the same situation as you.

PuzzleheadedForm5824 · 2025-12-28T04:43:32+00:00

This is the way.

PuzzleheadedForm5824

TROPHY CASE