Replies

1. 
   MarkH | Oct 13, 2011 09:17am | #1

   You probably need a vapor barrier on the crawl space floor, sealed to the walls and post footings. 

2. 
   Amish Electrician | Oct 13, 2011 11:39am | #2

   You closed up the crawl space, and it smells musty? And you are asking why?

   It's musty for the same reason basements are musty: not enough ventilation, too much water.

   Gee, maybe they knew what they were doing when they installed the vents. Maybe you should send the remediation bill to those who gave you the bad advice, and see what they say.

1. 
   KDESIGN | Oct 13, 2011 12:29pm | #3

   Venting vs. Sealing

   I suppose that if it were possible to hermetically seal a crawl space, starting with a dry condtion, that might prevent mold growth, but that seems like a practically impossible objective.  I am surprised that Building Sciences would suggest that approach.   I suppose that if you never had to enter the crawl space, you could seal it to the extent that any mold or musty smell would not affect the rest of the house.   

   Even with the most diligent moisture barrier techniques, it seems like it would be impossible to keep a crawl space completely dry.  It is true that open vents will allow moisture to enter on humid days, but the vents will also allow drying on dryer days.  For the humid days, I would provide active mechanical ventilation and/or a dehumidifier. 

3. 
   DanH | Oct 13, 2011 06:46pm | #4

   Crawl spaces are SUPPOSED to have a musty smell.

4. 
   JimB | Oct 13, 2011 08:01pm | #5

   Building Science actually recommends

   a conditioned crawlspace; that is, one which has an impermeable barrier on the ground, is insulated and has a method of air exchange with the house.  In other words, they recommend that the crawlspace be treated as a basement with less head room.  Removing or sealing the foundation vents is only one part of the equation.  This is discussed a lot at the Building Science website.  Here's one publication: 

   http://www.buildingscience.com/documents/reports/rr-0401-conditioned-crawl-space-construction-performance-and-codes/

5. 
   crosscountry | Oct 18, 2011 01:03pm | #6

   sealing crawl space floor vapor barrier at walls

   1. Thanks Jim B for the Building Science link as it was very helpful to me as I'm trying to seal and insulate my crawl space as well.

   2. The Building Science (hence forth refered to as 'BS' but in no way do I mean to demean the website) link states the 'floor'  vapor barrier should be 'Mechanically' sealed at the walls, and references 'attached with wood' in one diagram. Do I need to be concerned about the moisture being 'contained' by the vapor barrier between the wall and installed insulation? Should the floor vapor barrier be secured to the crawl space side of the wall insulation, or directly to the wall (with insulation laying over the top of the seal)?

   3. Since I don't have a vapor barrier, the BS site recommends sealed rigid insulation next to the face of the sill, then unfaced insulation over that. But I was going to install poly sheet over the unfaced batts. Will doing both creat problems? And will I have problems if next year I add rigid board to the exterior?

   Thanks.

   Jeff

1. 
   xxPaulCPxx | Oct 19, 2011 11:33am | #7

   You want to seal to the concrete walls, not to anything over that.  You are keeping water OUT of the space you want to insulate... getting your insulation wet isn't going to help you - neither is getting lumber framing wet.

1. 
   crosscountry | Oct 25, 2011 03:28pm | #8

   sill insulation

   Building Science diagrams for crawl spaces without exterior insulation show the interior faces of the sill 2x4 covered with a combination of rigid board and fiberglass. Is it not necessary to face all the interior faces with rigid board/sealant? If I did seal the interior faces, would that be bad?

   I've crawled into my crawl space of the addition to my 1937 cottage and sealed rigid insulation between the rim joists. I was disappointed to not only find no sill gaskets, but that the sill rests on cinder blocks that are not sealed as well. So I sealed both the sill and the top of the blocks with combination of frigid board and foam sealer.  A small face of interior sill still shows. I plan to cover it with fiberglass.  Would I be better off if I sealed the all the sill face with the foam sealer?

   There's also a 10' section where the sill rests on a 4X6 that rests on two rows of blocks. I'll have to use a wider strips of rigid board to seal the blocks, but a good 4" of the 4 x 6 face would be exposed (again to be covered by fiberglass). Should that face be sealed with rigid board and  foam?

   Thanks

   Jeff

1. 
   DanH | Oct 25, 2011 07:53pm | #9

   I've crawled into my crawl space of the addition to my 1937 cottage and sealed rigid insulation between the rim joists. I was disappointed to not only find no sill gaskets, but that the sill rests on cinder blocks that are not sealed as well.

   What did you expect to find in 1937-vintage construction??