Basement Insulation Question - Massachusetts


Old 03-13-12, 07:15 AM
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Basement Insulation Question - Massachusetts

First, Sorry for topic that I am sure has been discussed in numerous areas but everywhere I read it is all over the place and I am no more prepared to make a decision that I was prior to reading...

I am refinishing a room in my basement and have heard conflicting info on the use of a vapor barrier. A little detail... The basement wall is concrete blocks and the basement itself has zero water issues. Normal massachusetts basement in terms of humidity but a running de-humidifyer keeps the air nice and dry.

The room I am refinishing is only have of the basement. I have followed all standard code for framing and am now insulating and need to know about the vapor barrier and if I should use.

I have heard both sides of the story from contractors... Yes to use it and no do not. When the answer is yes the reason is it cant hurt given the uncertainty on how moisture will be and when I am told not to use it is because it will trap moisture inside the wall and not allow for airflow.

When framing the wall, I left a inch space between my studs and the concerete wall to A)get a square room and also allow for air cirulation inside the wall. I have used standard R13 fiberglass basement insulation with a paper backing. On top of the wall I plan to use sheetrock and plaster/skimcoat the entire wall and ceiling.

So, the question now is should a vapor barrier be used between the sheetrock and the insulation on the warm side of the wall? If yes or no why.

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Old 03-13-12, 03:32 PM
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The kraft backing is considered a vapor barrier in itself, although not as thorough as 6 mil plastic would be. Others on the forum more in tune with such northern climes will be here to give advice, so check back. If the walls are all below grade, the insulation may be redundant, anyway considering the walls are geothermally correct to begin with. Insulation won't hurt, however. Some consider using XPS glued to the block wall, which is a vapor barrier, but I have never had the call to use it here in the south.
Old 03-13-12, 03:48 PM
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The use of insulation in the basement is a good move. Having the ground next to the wall is better than air, but it is still cold.

The paper face is a vapor retarder. This will still allow some vapor to pass which is good.

Check out and learn all about vapor barriers and basements.
Old 03-13-12, 09:23 PM
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I'll let you decide:


Sill sealer for thermal/air/capillary break under p.t. (not waterproof) bottom plate: Pressure-Treated Sill Plates and the Building Code |
The faced batts shouldn't be used below grade unless thick foamboard first. Air seal the rims: Info-408: Critical Seal (Spray Foam at Rim Joist) — Building Science Information

Old 03-14-12, 04:51 PM
Join Date: Aug 2009
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The Sill sealer article is not accessible.

Interesting about the air gap. I thought the gap is needed to keep the wood away from the moisture coming through the foundation. I guess you keep the wood away, but not the insulation.
Old 03-14-12, 05:51 PM
Join Date: Mar 2005
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The vapor barrier and air gap questions will never go away or be resolved because of the variability of conditions and geography, so national practices are not meaningful.

In my opinion, most basements/semi-buried and walk-outs end up getting over-insulated if they are used as a living space. The temperature difference in the winter between the two sides of the wall is so minor compared to above grade lightweight construction, it is better to spend the money upstairs. One thing forgotten is that an over-insulated basement gives absolutely no benefits in the summer if the living space in the home is air conditioned. With reasonable air and return system, there is a benefit of mixing the cool air from the returns and getting the benefit of lower cooling costs. - I run my fan 24/7 during the heating season and set it on auto for the cooling season. We open up the house when it is comfortable outside (temperature and humidity) and then shut it in when the conditions change. For us the thermal mass/inertia of the concrete walls and the soil (always over 55F average in the winter) is a real cost effective benefit.


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