drywall install over extruded foam on basement walls

12 Replies

was going to glue 2" pink foam on bottom 24" of exterior block basement walls,,, then have electrician run conduit on top of that horizontally for outlets. Then foam on up to top of wall and rim joist area gets little rectangles (2 layers for 4" total). then great stuff all cracks and creases.

then glue drywall to that. Some people say that wont meet code,,,needs mechanical fasteners. Anyone do this? Was also told a large home builder in Omaha which is much larger town,,does exactly that!!

Does this work? Does it pass YOUR code? code inspector here likes to make up his own rules sometimes.

city threw me a curve today. I called and explained how I was going to do this including electrical. Inspector says sounds like a good plan and should work well.

I glue bottom 2 foot of 2 inch foam on half the house and the phone rings. Inspector says whats the r value of the foam. Its R-10. He says has to be minimum of R-14. So I said have to add another layer of 3/4 then. Well IF you glue 2 " to wall,3/4" to that, and drywall to that, the manufacturer (Owens Corning ) has to certify its a allowed acceptable use of their product. OR a structural engineer to sign off on it!!! 20 years ago that cost min of 750 bucks.

Only way its automatic to the city is to 'stud' the wall inside the first layer of foam. Not knowing I had some on already he says glue 1" to wall,,,then stud and put insulation in stud bay.

Putting 3/4 or 1" inside a 3 1/2 " wall seems goofy waste. Thought of asking if I put studs on flat...or use 1 X 3 firing strips BUT in any event the extra 4 r value is not continuous, broken by fir or stud.

Next problem is new heat ducts are close to blocks in places and NO room for any of this,,,then what??? Maybe I can alter some of them to make room.

This is turning into a nightmare OR huge learning curve, whichever comes first!!! What am I missing??Any suggestions???

What about the vapor barrier

the extruded polysterene foam insulation is supposed to be vapor barrier as well as insulation. Was told if I put plastic over block it causes and traps mold. Same way with dry lock waterproofing paints. will see what woulda,shoulda,coulda comes up.

plastic is for fibergass insulation and stud walls I am told

don i think i just did a basement like this..welli think so..kinda got lost in your post..sorry lol...we used treated 2x4's nailed into block with masonry or tapcons...they were put on the face 16 inches on center..then we cut the dow board, which has an R rating of 4 per 1/2 inch if i remember correctly, into 16 inch X 8 foot strips..glued that between studs onto wall..after that set, we glued another row of dow board onto previous dow board..this added up to 1 inch of dow board, which still sat lower than the 2x4's...even if you need to hit a higher R value though, you can glue a 3rd or 4th as long as it holds..just need to use longer sheetrock screws..using the 2x4's on the faces also allowed us to wire into the wall into the wall instead of running conduit above...just curious, what R value did your inspector allow for the block??


don, just remembered..another option is you can have an insulation company spray it..it gets very expensive though..for me, it was like 2000 bucks i think for a 300 sq ft basement room..there's all types of unconventional insulation methods..they just usually cost more..i'd call the inspector and see if he's cool with the dow board..4x8 sheets are 10 bucks at lowes and you can layer them on top of eachother..at least here you can, to get the proper insulation R value


I would think if you used all glue and not mechanical fasteners that over time the moisture migrating through the concrete from the outside soils would cause the glue to eventually delaminate. However, I'm from Texas and, therefore, not very familiar with basement construction techniques.

Originally posted by Brian Hoyt:
However, I'm from Texas and, therefore, not very familiar with basement construction techniques.

What, you can't have basements in Texas because the oil comes gushing out once you start digging? :)

Anyway, Don: In your version without studs, how would you mount the electrical boxes?
When using the foam board in the stud bays, I think you would seal the corners like you would seal the gaps/seams on the glued on board. That would prevent the breakage on the insulation, I think.
But then I am not an expert (yet), I was just starting to look into the whole basement remodeling thing as mine is due to get done April or May.
I've only heard in our area that screwing studs flat to the basement wall and putting the drywall on that is not up to code. Not sure why, if lack of of proper insulation, or whatever mysterious reason inspectors sometimes come up with.

Uwe K.

Isthis the same Uwe as Germany Uwe? How did you get to Wisconsin?

Cant put untreated wood agaINST ANY CONCRETE,IT WILL ROT.

need vapor barier first which 2" foam is very good at. Put furring strips like 1 X4 against 2" foam and fill between to get your r-14 as is required here.

stay away from fiberglass batts below grade,,,basements etc because all it is is a stinky mold and mildew catcher. once its damp its toast

I would think that there is a way to secure insulation and drywall or another finish to a block wall to meet code but probably costly and/or cumbersome. There may be questions in between inspections; framing, thermal and then finish.

I wouldn't think of NOT mechanically fastening the wall assembly. It will move with humidity and temperature change. I may consider a small area though.

What I've used before is polyiso(TuffR). It's a foiled face board insulation that has a higher R value than polystyrene. You might be able to get away with only 2" of insulation. If you come up short on R-Value you can add insulation where possible; rims could get R21 fiberglass.

Essentially you can compensate for a lack of R-value in one area by putting additional insulation else where; you're looking for the total U-value of the the entire envelope.

Although more costly, I prefer metal framing. I find working with it much quicker and cleaner. With metal, you can use track and studs or only 'Z' furring at 24" on-center. When using 'Z' furring, you will be using less metal than track and studs but you would want a powder or gas actuated gun.

Hopefully the job is done for you.

yes we are all done now except for hanging the drywall. Ended up completely covering wall with 2" foam. Screwed electrical to block walls both boxes and conduit. Went with a 2 circuit in one conduit all aroubd the whole small basement two feet high off the floor.

Then recessed tapcons into 1X4(only full 3/4 thick straight lumber could find). Had to recess tapcons cause whole town didnt have long enough ones. screwed tops and bottoms conventionaly. Put a treated 1 X2 all around the floor on concrete t eliminate rot of white wood on concrete.

Cut 3/4 foam to fit between 1 X4's tight. Filled all voids and spaces with foam. Next is to get inspector thru and approved and get a partion wall on one end of the two bedrooms down there, complete with the closet and the regular doors for each.

My experience using ANY fiberglass insulation has never been good,,,it acts like an air filter and then turns stinky.I have found code is one thing,,,long lasting operational function is most important. Code is good,but not alwats good enough. oh I also stuffed a 2 layer of 2" foam in rim joist area. Going to fill any cracks with spray foam,Great stuff.

Lots of time consuming work but looks good now we are on downhill swing.

Don, yes, same Uwe ans Germany Uwe. Came to WI with a student exchange and got stuck somehow :)

With fiberglass, if yo have a proper vapor barrier behind it, it shouldn't start stinking and rotting - in theory. All that extruded foam sounds expensive.

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