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hammer..bang 09-01-2012 09:54 AM

Another Basement Question
 
Hello,

I know this has been asked and probably answered 100,000 times but I'm still confused. We planned to DIY our basement but haven't had time doing the rest of the house so we are cheating and hiring a contractor to do put in a bathroom, framing, insulation and a few other things. We interviewed several contractors who each had a different way of doing it. Initially we planned to use foam boards and possibly bat insulation. The basement stays a reasonable temp. all year round and is comfortable in the summer except humidity (we do run a dehumidifier). I am dry locking the walls just to be safe but we think we resolved the water issues a few years ago.

1/3 of the basement is underground and the rest is above ground (yard slopes). Can we get away with just using bats or is foam much better? The current contractor we want suggested bats. What is the "best" of either out there? I need something low smell (reading other threads here about the smells). I was looking at the Dow Safe Touch. Something with some sound barrier would be nice as we have a workshop down there with the table saw and all that good stuff.

Thank you in advanced for your help.

oh'mike 09-01-2012 10:27 AM

I use fiberglass bats with a vapor barrier in the conditioned side of the walls---

Your location is needed as insulation requirements differ in really cold areas --Canada has some additional requirements,I believe.

jklingel 09-02-2012 12:10 PM

I'd read on buildingscience.com. I think you'll see that rigid foam is highly preferred, air seal well, and no vapor barrier. A Canadian study, where a vb seems to be "required" (but really is not if you can prove you've air sealed) showed that the walls w/ a below-grade vb had more moisture in the insulation that the ones without.

hammer..bang 09-08-2012 10:46 PM

We are in the DC Metro area so we get cold winters but it varies. Nothing like Canada but I prefer overkill when possible. We did 1/2 inch foam prior to our insulation upstairs prior to residing but none of that covers the basement area. Our original plan was ridged foam when we planned to DIY but the proposal with the contractor just used bats. My concern, which is why I asked was that you get the mold/moisture behind a plastic vapor barrier and I want to obviously avoid that at all costs. I only specified if we used bats I wanted to use ones that were not fiberglass and wanted a "safer" one. I'm sure he'll do what ever we would like as he gave us a great proposal with lots of flexibility so we can DIY want we want to but we were just debating what was best. Only about 1/2 the basement is underground. I was concerned about sound too as we have a tool workshop down there and the noise carries.

Thank you.

Gary in WA 09-09-2012 12:20 AM

Fiberglass/poly is Case #3, pp.7; http://www.buildingscience.com/docum...study-analysis

Gary

AllanJ 09-09-2012 07:34 AM

The problem with vapor barriers in basement walls is that the stud cavities are rarely if ever hermetically sealed. Any moisture that does get past the vapor barrier will remain behind there for a long time.

If there is a waterproofing coating on the outside of the foundation, that counts as a vapor barrier and there should not be a vapor barrier on the inside wall. If there is no waterproofing, there is a good likelyhood that some of the time moisture from the ground will be coming inside through the concrete foundation.

Whereas for upstairs walls, any moisture from inside that gets into the walls will find its way outside through the siding.

hammer..bang 09-09-2012 10:40 AM

Allan, that is my exact concern so what is our best bet. I don't want spray foam due to the smell and I don't fully trust it long term. I am dry locking the walls with at least two coats - may do a third with a sprayer as its very hard to get every little cranny where I can get to it (some of it is almost impossible with the pipes but I'm hoping when those get changed out I can quickly paint). We haven't removed the paneling yet on 1/2 the basement so I don't know what we are looking at there in terms of dry lock. Are we better off with ridged foam or ridged foam and then insulation? The basement gets cold in the winter but except for Dececember/Jan. it is not terribly cold and it has/will have heat/ac. Summer it is usually comfortable. I do worry about water in some areas coming up the floor. We are just going to DIY a cheap floor so it if gets ruined no biggie and we just replace it. We are also adding a second bathroom which will bring some humidity too.

AllanJ 09-10-2012 08:16 AM

You must correct the problem of water coming up through the floor or between the floor and foundation wall. You may need to install a perimeter drain system (a kind of French drain) with sump pump. But first check around the house during a heavy rain and find and soon thereafter correct all issues with water ponding up against the house.

If you put down a floor and water seeps up between the wall and floor, then more moisture will go up into the wall.


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