Getting started on a basement


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Old 03-25-10, 07:28 PM
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Getting started on a basement

I'm looking to insulate my basement and I want to see if you guys think I'm going in the right direction. I live in New Hampshire. The house is about 35 years old, poured foundation, no cracks, no leaks. However, I had a serious humidity issue down there. It was so humid, I would get water puddles on the floor (not the walls) during the summer. That is, until I put a dehumidifier down there and had central air installed. It's been bone dry for a year since then. My rim joist is spray foamed already. So I was going to frame the basement and batt it (unfaced with no VB). Now, after reading so many posts, I'm wondering if I need a vapor barrier between the insulation and drywall and/or XPS against the concrete. I figured with no VB, I could keep everything drier down there with the dehumidifer. The more I research, the more I 'm confusing myself. If you can set me straight, I'd appreciate it.
 
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Old 03-26-10, 02:54 AM
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Hi beachhead2, the reason it is dry is your efforts to remove the moisture (water vapor) as it passes through the walls and floor. Cover either of those surfaces with a VB and the moisture level behind the vb will rise to match the soil outside. It will then find a way through the vb and possible be a problem.

I would go with the rigid foam, pink or blue, with no foil or plastic covering so that moisture can continue to pass through and evaporate. It is a slow process, but if blocked or restricted, the moisture/water will accumulate. If you wanted to block it, that is what should have been done 35 years ago on the outside, and not just a coat of tar. My generation, so I know they weren't concerned back then.

Some of the building science links that are all over the forum provide some good options. I prefer to limit the rigid to exposed concrete, plus one foot below grade. If you sheetrock, look for paperless. As time and funds allow, address all drainage issues from the outside.

Bud
 
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Old 03-26-10, 10:06 AM
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Thanks, Bud. That makes sense to me. So if I go with the pink/blue xps, do you consider fiberglass batts overkill/unnecessary? It gets pretty cold around here. I wouldn't mind having some pretty beefy insulation. And along those lines, I never see talk of framing on 24" centers. Do you see any problems with that? Seems like it would save a little $/time. Thanks for the advice.
 
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Old 03-26-10, 11:21 AM
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In the exposed concrete plus one foot zone, more is better. If you read through the building science links, I believe they even use foil faced rigid in the upper areas, so kraft faced fiberglass should be ok and easier to install. I just checked that and Fig 11 on this link shows the foil faced.
RR-0202: Basement Insulation Systems —

As for framing 24" oc I see no problem and limited gains. Upstairs where straight walls are really important I would shift to 5/8" drywall, but in the basement 1/2" should still be ok.

Bud
 
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Old 03-26-10, 04:02 PM
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Thanks for that. And thanks again for leading this horse to water. I printed that and read it over. That's good stuff.
 
 

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