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mcwolfe6 02-21-2010 08:28 PM

Basement Insulation Plan
I have come up with a plan on how I am going to insulate my basement based on what I have read on this site and on the Building Science website and would like to get some feedback from the folks on here. I also have a few questions so if you can help me out with them I would appreciate it. Here goes
First I am going to cover the concrete slab floor of the basement with 1 inch XPS board and use adhesive (liquid nail) to hold it in place temporarily. I am doing this to ensure a warm floor once we have the room carpeted.
Next I am going to put 1 inch XPS on the exterior walls of the basement, all of which are cinderblock and below grade (no water issues). Ill use liquid nail and tapcons to secure the XPS to the wall and Ill be sure to insulate and seal the rim joists and seal plates . Two of my exterior walls have the sewer line running tight along them and I wont be able to get XPS behind it so I will butt the XPS up against the sewer line and use spray foam to get in behind the pipe as best I can. Ill seal all seams with Tyvek tape.
Next I plan on putting inch Tongue & Groove plywood down on the floor over the XPS and anchoring it with Tapcons (this will also secure the XPS).
Ill then frame out my walls with wood 2x4s, fill with unfaced bat insulation and cover with gypsum board. The base plate of the wall will still be pressure treated even though it will be sitting on top of the XPS and plywood subfloor. Two of my framed walls will have a two inch space between the XPS and the wood framing due to the sewer line and my other two walls will be flush against the XPS on the wall.
Thats pretty much it for my plan, now for my questions
Do I need to use Plywood for my subfloor or can I use OSB instead since I will be carpeting the entire room?
There is an opening on one of the basement walls that is access to the crawl space under our laundry room. It is roughly a 6x3 opening. Is it acceptible to cover the opening with XPS and put an access panel in the wall in case I ever need to access the crawl space? Or is there a better way to close off this space?
Last but not least, when I anchor the framed walls to the floor can I just anchor them to the plywood since it is already anchored to the concrete slab or do I need to anchor the walls down through the plywood and XPS into the concrete slab?
Thanks for any feedback you give.

ccarlisle 02-22-2010 06:52 AM

1/2" plwood won't do on the floor, too spongy. Use 5/8 T&G or 3/4"...

mcwolfe6 02-23-2010 10:07 AM

Okay, so 1/2 inch plywood won't do. I'll adjust that. Any other feedback?

Mudball 02-23-2010 09:02 PM

From all that Ive read and will be doing it sounds like your right on track. I cant help with the entrance or flooring but would like to add that I dont believe it will be necessary to screw your foamboard to the wall but rather consider a special foamboard adhesive that most big chain stores carry and should serve your purpose just fine. With the right liquid nails product you probably wont burn the foamboard but make sure you have the right one. Also you might want to consider a cement based type sealer paint like UGL Drylok or Kilz before the foamboard is applied. There might not be water issues now but it wouldnt hurt to apply it before all that other work.
Good luck.

mferguson0414 02-24-2010 05:05 AM

It sounds like you have read ALOT of information on your process for insulating your basement. I read your post twice to verify I didn't read this, so I would suggest that you also tape any of the seams created on the floor or wall, and where the floor meets the wall. That is all..

ctkeebler 02-24-2010 09:28 AM

I would just make sure that the liquid nails glue can be used on the foam. Some glues eat away the foam. I know PL makes a glue especially for foam board.

PL300 Foamboard Adhesive
PL 300 provides dependable adhesion of foam to all types of surfaces, including wood, fiberglass panels, concrete, brick, metal and drywall. It is compatible with foam board insulation. It permanently joins the foam to the substrate without compromising the insulation value of the foam.

High Gear 02-24-2010 11:26 PM

PL-300 for made for foam board and works well , comes out easy.

PL-Premium is a much stronger glue ( also rated for foam ect. ) but its a

bear to squeeze out of the tube unless its warm .

Buy a large size caulk gun , tubes are cheaper ( per oz. )to buy that way.

IMHO forget the tape and just caulk the groove edge to make the seal.

Mudball 02-25-2010 05:40 AM

Also you might want to consider 2" thick foam board for your area. I dont think youll regret it.

mcwolfe6 03-01-2010 09:14 AM

I appreciate all of your feedback.

I will look into the PL300.

The reason I am using the 1" foam board is because according to the Building Science website the perm rating should be 1 or better and anything thicker than 1" doesn't meet that perm requirement.

I will be taping all of the seams on the wall and floor insulation.

I bought 3/4 inch t&g plywood for the floor but there isn't any plywood clips for this size plywood at the big box store. Do I need the clips for this size plywood since it's much more rigid than 1/2 inch plywood or should I still use them?

Thanks everyone. Keep the feedback coming.

Gary in WA 03-01-2010 10:10 AM

"Two of my framed walls will have a two inch space between the XPS and the wood framing due to the sewer line and my other two walls will be flush against the XPS on the wall." ----- You need to fire-block the top of the wall from the joist spaces and every 10' along the wall sideways. Add plywood, 3/4", cut into rips for the gap between top plates, existing and new, BEFORE you add the new wall, much easier. T&G plywood does not require ply clips for strength. I would not use OSB over real plywood between the soil and heated space due to moisture mitigating through the materials:

Be safe, Gary

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