Basement insulation/vapor barrier

[TomC750]

We have a 1100 sq' basement, block wall tarrred on outside with another barrier as well. We are in eastern TN. The east wall is exposed to daylight. A contractor (who never showed up after the initial visit) said insulation was not necessary. I disagree, as this morning with a 25* outside temp, there was a 12* temp difference between the east and west walls. The north and south walls were within 2* of room temp. I am thinking I'll just insulate the east wall with styrofoam between the studs mounted flat. Thanks to yeldogt for reminding me of that, I had done that many years ago on a concrete wall and used spring nails to attach the studs.

I may be answering some of my own questions here, but I do wonder about vapor barrier. The basement is very dry but a small amount of mold has appeared on a small area of the east wall during a previous winter. Also, what fastening method for the studs? I am behind on present methods! Thanks for any and all responses
Tom

 

[Mzungu]

This video mostly applied to below grade basements, but nonetheless is good information.

 

[billconner]

Spray foam is best choice but also most expensive. Id look at rigid foam with integral framing/nailers, like InSoFast. Or just glue foam on walls, seal, and stud (2x3?) inside.

 

[TomC750]

Thanks to Mzungu and Bill. This was helpful. I will probably use Tapcons for the stud attachment. It will cost a bit for sure. I will add that the core holes have been filled with concrete. Should provide a more reliable hold for the Tapcons.

 

[Mzungu]

I went through this same decision making process myself on a walkout basement in climate zone 6. I ended up hand excavating and going with blueskin wp200, 2 inch xps exterior insulation and 1/2 inch pwf plywood on 3 walls which were block. The daylight wall is 2 x 6 with plywood 1.5 inch comfortboard and siding. I finished the interior 3 block walls with studs and drywall no insulation. The 2x6 wall was insulated vapour barried and drywalled.

 

[75gmck25]

This is a picture of what I did for insulation in my 1940 vintage basement. 1" foam glued to the wall, 2x4 framing in front of it, and rockwool inside the stud bays. The stud walls are only attached at the top (screws into the joists above) and at the bottom (power nailer into the concrete). There is a foam layer under the base plate and it is pressure treated lumber.

 

[PoorUB]

Always insulate!Insulation is one of the cheapest improvements you can do as you pay for it once.
Anything is better than nothing. I am surprised a contractor said no. In a full basement the insulation requirements are low, but do something. Even 1-1/2" foam between furring strips will help.

 

[TomC750]

Yep, Gonna do it! Thanks PoorUB. I can hear your J D in my head. I grew up with them.

Tom

 

[Firebrick43]

I would not attach studs to the foundation. Personally I would use insofast but if you have to do a stud wall put some xps between the stud wall and the foundation like 75gmc shows above. It gives water a possibility to fall to past the slab and not be absorbed by the wood or insulation. Install the xps with dots of adheasive, just enough to keep it in place and build/raise a stud wall into place. I would place some foam under the wall as well. Screw the bottom sill thru and to the floor and the upper sill to the floor joist above. Dont need to attach it to the wall at all.

 

[mrpizza]

I have a basement in a 1965 house. I did a full interior french drain, I believe I will closed cell spray foam the walls, with the studs 1/2" off the wall so the foam seals behind. Any issues with that plan?

 

[Firebrick43]

I have a basement in a 1965 house. I did a full interior french drain, I believe I will closed cell spray foam the walls, with the studs 1/2" off the wall so the foam seals behind. Any issues with that plan?

The spray foam holds the water, even though its "closed cell" it will slowly migrate thru it. If you use xps the water hits it and falls to the perimeter french drain and is gone.

Insofast is basically a foam sheet with plastic studs already inbedded in it and performs the same way.

 

[mrpizza]

I do have plastic that goes from the top of the wall all the way down into the dimple board at the footer.

That Insofast would run me over $3k it looks like

 

[mike93lx]

I did a basement with 2" foamular, 1x4 and spring nails. Drywall on that. When pounded in, the nails were rock solid and a lot cheaper than tapcons.

Doesnt make it super easily to deal with leveling, but it turned out pretty decent.

 

[kaymccampbell]

When you're setting your base plate for the wall, just remember to isolate it from the concrete. When I redid the basement in the rental, I used kleer or azek chunks under the plate. I left some gaps between the chunks, so any water that needed to could make it to the perimeter drain.

 

[Mzungu]

I have a basement in a 1965 house. I did a full interior french drain, I believe I will closed cell spray foam the walls, with the studs 1/2" off the wall so the foam seals behind. Any issues with that plan?

You are better off and probably cheaper to use 2 inch xps behind the stud wall. You can use 2 x 3 studs to make up for some of the extra space the 2 inch xps takes up. Use a strip of xps to isolate the walls baseplate from the concrete floor.

 

[mrpizza]

You are better off and probably cheaper to use 2 inch xps behind the stud wall. You can use 2 x 3 studs to make up for some of the extra space the 2 inch xps takes up. Use a strip of xps to isolate the walls baseplate from the concrete floor.

The dimple board sticks up about 1/4 to 1/2 inch above the slab along the wall. How would I go about getting any water to drain into that area? Raise the panel above that lip, frame, then spray foam that lip on the bottom? I'll post a pic later of the wall

 

[Mzungu]

The dimple board sticks up about 1/4 to 1/2 inch above the slab along the wall. How would I go about getting any water to drain into that area? Raise the panel above that lip, frame, then spray foam that lip on the bottom? I'll post a pic later of the wall

If I'm picturing it correctly you could just notch the xps panel on the backside enough to clear the dimple board. Then run a bead of polyurethane sealant or if the gap opens up do to an uneven floor you use a low expansion foam.

 

[mrpizza]

This sticks up and out a tad.

So would I ditch the plastic altogether? My wife is worried about any water that may come in and miss the drain and end up on the floor. But the basement has been bone dry since I completed the French drains all around.

 

[Mzungu]

It's not

This sticks up and out a tad.

So would I ditch the plastic altogether? My wife is worried about any water that may come in and miss the drain and end up on the floor. But the basement has been bone dry since I completed the French drains all around.

It's not going to hurt anything by leaving the plastic on. You can fasten the xps through it using a variety of different fasteners approved for that purpose. I would still run the xps tight to the floor and seal it with caulking.

 

[TurnipTruck]

I insulated my daylight block basement with 1.5” foam friction fit vertically with a 2x4 wall (pressure treated sill) in front of it and stuffed with R13 fiberglass. The stud walls were sill-sealed and screwed to the concrete floor and screwed to the joists above.
We DID NOT use vapor barrier on the underground walls (despite being in zone 8) as the block is assumed to be vapor porous except when underground.This is a FLIR pic of the old bare uninsulated block basement wall.
That is an upright 55gallon drum near the door jamb at the extreme left, and it’s -22*F ambient.
The wall is almost 60*F warmer than ambient!

 

[mrpizza]

It's not

It's not going to hurt anything by leaving the plastic on. You can fasten the xps through it using a variety of different fasteners approved for that purpose. I would still run the xps tight to the floor and seal it with caulking.

I guess I am overthinking any moisture coming down the board and not getting behind that dimple board on the footer?

It's a block basement and I drilled all the block cores and joints to drain under that dimple board.

 

[Mzungu]

I guess I am overthinking any moisture coming down the board and not getting behind that dimple board on the footer?

It's a block basement and I drilled all the block cores and joints to drain under that dimple board.

If the moisture problem is that bad, you should run the dimple membrane up the entire wall. If you plan on finishing the basement you have to insulate it. The best way is with xps. For myself having a serious water problem I would have spent a little extra and tackled that issue from the outside. I actually just dug up 40' feet of 9 foot block wall foundation on my own house this past summer. I didn't have a water problem, but I wanted to insulate from the exterior. I ended up installing WP200 as the first layer then 2" xps, then a layer of 1/2" PWF as the final layer.

 

[mrpizza]

The moisture problem was bad, but all evidence since shows that I fixed it with the French drain system.... 12+ months I think since it was done.

In my wife's mind, anything we put back on the walls will immediately mold and begin destroying the wood framing and ruin the health of the family.

 

[Mzungu]

The moisture problem was bad, but all evidence since shows that I fixed it with the French drain system.... 12+ months I think since it was done.

In my wife's mind, anything we put back on the walls will immediately mold and begin destroying the wood framing and ruin the health of the family.

That's why if you are finishing the basement you need to contain any moisture behind the 2" xps. Without the xps your drywall and framing has the potential to mold from A) Moisture that may come through the block wall. B) Moisture in the conditioned air that moves through the drywall and then condenses on the cold block wall.

 

[Firebrick43]

The moisture problem was bad, but all evidence since shows that I fixed it with the French drain system.... 12+ months I think since it was done.

In my wife's mind, anything we put back on the walls will immediately mold and begin destroying the wood framing and ruin the health of the family.

Or give the ultimate piece of mind, use no wood or products that can mold period. Such as insofast and an exterior paperless drywall or even xps and apply a synthetic stucco to the face of it or culture stone/verneer brick which is basically synthetic stucco.

 

[mrpizza]

Looks like xps sheets is the way I'll go. Would it also be good to insulate the stud wall on top of the XPS or overkill?

 

[Mzungu]

Looks like xps sheets is the way I'll go. Would it also be good to insulate the stud wall on top of the XPS or overkill?

Do you mean the rim joist? Absolutely, it's a major source of heat loss. Lots of youtube videos on that one.

 

[mrpizza]

I mean in the stud walls that I will build over the XPS insulation. I was planning on spray foaming the rim joist to seal and insulate it.

 

[Mzungu]

I mean in the stud walls that I will build over the XPS insulation. I was planning on spray foaming the rim joist to seal and insulate it.

Okay, when you said top I literally thought the top. Yes you should also insulate the stud cavities. In your climate zone the recommendation is r19. So now is when you could spray foam, fiberglass, or rockwool. If you use 2x4 studs Rockwood is a great option. It is fire resistant, doesn't sag, and rejects water.

 

[RPhil]

2" XPS will give you R-10 and be a vapor barrier all-in-one. It is what I am using in my basement. You can then do the walls however you want (2x4, furring strips, steel studs, etc.). The top part of the block wall could be the harder part to get properly insulated and sealed due to clearances to your joists above, depending on construction. I recently had my home air-sealed, so my rim joists and sill plates were sealed, but there was a lot of overspray on the joints- which meant it would be hard to slide in XPS on top of the block towards the sill.

I elected to put down a vapor barrier on top of the block here, which overlapped the XPS and was taped at the seams. I then slid rockwool into the cavity.

I used PL300 out of a caulk gun to attach the panels to my block wall. It is a specific adhesive meant for use with foamboard. It was not a fun process and can be difficult to hold the panels in place easily and with pressure across their entire surface. I am roughly halfway through and just discovered that Great Stuff makes a Construction Spray Adhesive that is rated for concrete and foamboard. I am planning on using that for my remaining XPS sections.

Good luck!

 

[toyotadriver]

Best way to adhere foam sheet to concrete is with low expanding polyurethane foam in a can. Nothing is better IMO