Advice on basement insulation and vapor barrier?

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Posted by: from Nanticoke
9/2/2014 at 6:37:14 PM

I want to finish our basement. I live in home built in 08 on north shore of Lake Erie. Not sure what was done if anything to outside of exterior poured concrete foundation but done by pros. Inside basement we have R 12 fiberglass insulation covered by super 6 poly in a horizontal fashion about halfway down the walls, the bottom half is bare. A portion of those walls are framed in using 2 x 3s which are tight against the insulation and barrier.

This is my starting point so forget rigid foam or anything other than batt fiberglass to finish which my research says is the way to start if brand new. The basement and current insulation is dry as a bone and has been for 5 years.

Should I only fill in the bottom half of walls and then cover that with plastic?

Should I go full height with batts over the builder installed stuff on upper half of walls? If yes to this last question should I slash the previous vapor barrier first?

Probably millions of basements have been done with batt insulation and vapour barrier. Does this type of reno spell disaster due to mold as a lot of articles indicate?

Again, basement is currently very dry so why can't it be finished and stay that way?


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Date/Time9/2/2014 at 9:04:16 PM

I would suggest you start by reading this article. Good info from a reliable source.

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Date/Time9/2/2014 at 9:49:21 PM

Hey Jim,

There are lots of different schools of thought when it comes to basements and insulation. Ultimately, the decision usually comes to budget. Your best bet is to remove the batt and install a 2lbs spray foam insulation. 2 lbs foam is dense enough that it acts as its own vapor barrier, 1 lbs foam does not! This is probably your most expensive option.

If that doesn't sound like the way you want to go, I would remove the 6 mil poly and install another r-12 batt on top along with black tar paper and r-24 batts on the bottom. Your insulation value is now superior to the existing r-12 and your heating bills should reflect that.

But don't stop there! Use a Dri-Core system or alternate on the floor and you will maximize the warmth of your basement!

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Date/Time9/2/2014 at 10:43:55 PM


I am going to suggest a cost effective and very effective system I use all the time when finishing a clients basement. (My own as well).

First remove all the plastic, insulation and 2x3 that exist now.

I assume you have steel beams that will need to be boxed in, you can use most of the 2x3's for that.

Now stop at Lowes or another big box store and buy 2'x8' sheets of ridged blue foam core insulation. Buy the R-10. There is a specific glue to use..ask. Glue the foam directly to your concrete foundation. Carry it up over the base plates for your floor joists on the main floor.

Then use tuck tape and close every seam between sheets and tape the outer edges again the top of the foundation. This gives you the first R-10 plus your vapor barrier.

Now 3/4 0f an inch in from the blue board chalk straight lines down each wall. Measure across to be sure the room will be square. Use Blue board 2x4 lumber for your base plates when you build the walls. When you install each section use the 5" wide white foam under each wall and ramset the bases down. After you have finished building all you outside walls, and have run all electrical and plumbing, now you add Roxul R21 green insulation.

You now have R-31 insulation. An extremely good vapor barrier that will never allow moisture to contact you soft insulation.

Now as the previous poster suggested, You install Dri Core 2'x2' subfloor sheets. This way if you evr have water intrusion or even a burst pipe, the water will work under the plastic base of the wood panels and work its way to the drain in your basement. The floor is also insulated by this system. These are not inexpensive, but I swear by them. There are cheaper foam bottomed panels that actually provide more insulation value but water can not travel.

Remember, if you are not an electrician, get a certified one in to inspect all your electrical runs and hook ups prior to installing the roxul. Let them hook all the lines up to the main panel.

Hope this helps.


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