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Finishing Basement Walls, Insulation and Vapor Barrier

Finishing Basement Walls, Insulation and Vapor Barrier

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  #1  
Old 02-16-12, 04:51 PM
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Finishing Basement Walls, Insulation and Vapor Barrier

Hey Guys,

I am finishing the basement. I have cleaned and sealed the block foundation (below grade) with behr waterproofing paint. I will install dricore subfloor this weekend, and plan to start the framing next week.

My question is how to insulate the walls...

I have no water issues. Everything is patched and sealed.

I will leave an inch of gap between the 2x4 walls. I plan to cover the walls with sheetrock.

I'm under the impression that I can use batt insulation with no vapor barrier??? Is this correct? If so, what type of batting is best below grade?

Thanks,

Bryan
 
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  #2  
Old 02-16-12, 05:03 PM
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Bryan, if it is below grade it is geothermally correct to begin with. Insulation would be redundant. BUT if you want, use kraft batts with the paper facing the living area. It also gives you a manner of attaching the insulation to prevent sagging in the walls. If you can find it and would like to use it, try Roxul. IMO it is far superior to batt insulation. You would need to apply a plastic vapor barrier on top of your studs just prior to sheetrock. That will keep condensation behind the wall where it will dissipate on its own.
 
  #3  
Old 02-17-12, 05:05 PM
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I'd use p.t. bottom plate on a poly sill sealer for a thermal/air/capillary break. With rigid foamboard on the concrete, a vapor barrier is not needed/required. Code doesn't require v.b. in basements anymore due to problems with mold. Build the frame wall tight to the foam wall with fire-stopping studs every 10' lineally per code and solid wood over it to isolate the foam wall from ceiling bays above. Fiberglass and a poly v.b. is asking for mold on the wood studs and degrading the R-value up to 66%.

Gary
 
  #4  
Old 02-18-12, 02:05 AM
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I'm laying the entire floor with dricore before framing, so as I understand there is no need for PT bottoms plates as the plate will never come in contact with the concrete floor, correct?

I am leaving an approximate inch gap between the edge of the dricore and the block foundation. The framing will also have an inch between the block foundation and the studs. I was told to keep this area continuous with the subfloor gap for breathability. If I were to use rigid foam, it seems it would block the air flow from under the dricore and the wall space...

I understand the theory on avoiding the VB so that the moisture from behind the walls can difuse into the room through the wall... OK, but then what type of insulation would work best in the wall space???

I would assume non-papered non-fiberglass...

Truth be told, I am going to be selling the house in the near future as I am taking another job, and to be honest I don't want to break the bank on insulation as the space is technically geothermically correct as mentioned above. I do know that my local code requires insulation, i believe to an R13, but I have to check that number...
 
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Old 02-18-12, 04:39 AM
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Gary has another method of doing it. Although I prefer another method, your research will guide you to the correct method for your area and code concerns. I would definitely use pt lumber for the bottom plate. It isn't so much that it is in contact with the concrete, but it could be in contact with moisture from the leaking toilet, sink, or other water problems and will wick up the walls. Preventing this wicking will go a long way should you have a problem.
I would ask the authority who says they require insulation "why?". I would be interested in their answer. Not the answer you got from your mom when you asked it....."because I said so", but a fact based answer.
 
  #6  
Old 02-19-12, 11:23 AM
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As a basement specific contractor for the last decade, with 50 installs in 2010, I can tell you any vapor barrier used in conjunction with any organic materials is a mistake. Unless you can assure a perfectly tight fit between the source of the moisture (the concrete slab, or walls) and the drywall, wood framing etc.. the moisture will begin to grow mold pretty rapidly. Just the temperature difference between the finished and unfinished space will create enough moisture to grow mold. Avoid any plastic on the floor or walls. As far as insulation R-13 is standard with this type of construction, which is there to create a thermal break between heated space and the cooler wall. If you do not insulate more moisture will be created behind the walls leading to more mod issues. You can look at a basement system which has no organic materials like Superwall Basement Finishing Systems. Use metal studs and track. The wood will wick water and moisture up the walls as well. The studs are straight, lighter and there is bascially no culling of materials.
 
  #7  
Old 02-19-12, 07:17 PM
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I’d install the frame wall after the foamboard. Use a sill sealer to prevent capillary wicking because p.t. wood is treated against bugs and decay, not waterproofed: Pressure-Treated Sill Plates and the Building Code | GreenBuildingAdvisor.com

Having the dricore stop before the frame wall (w. sill sealer) will help air seal the concrete wall from interior air causing condensation (and the circulating air under the dricore). Leave the required ¼” gap at dricore/frame wall as per instructions (to let the air mix with room air). No gap from frame wall/insulation to foamboard for convective loops: MYTH: LEAVE AN AIR SPACE BEHIND THE INSULATION IN THE BASEMENT TO AVOID CONDENSATION.


The poly in basements is Case #3, pp. 26 and pp.49, see how they fare compared to Case #4 with just 1” of foamboard and no poly - pp. 29. Increase the foam thickness to reduce the moisture issues. From “worst-to-best” walls: http://www.buildingscience.com/docum...study-analysis

Dmar11b, I’m surprised you would plug your Superwall (Contractors only) on a DIY forum. I did get a chuckle seeing the little cartoon man with two drawings the same, but one flipped showing the “S” on his chest ---- backward. There’s quality control, you really should tell your distributor.

Gary
 
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