Replies

1. 
   MGMaxwell | Dec 07, 2009 11:15pm | #1

   Okay take this from DIY with crawlspace in the NC mountains. Mice love to live in the FG. I closed my vents as well because warm moist air in the summer condensed on the cool surfaces in the crawlspace. Since everything is tight I have no problems.

   If you choose to use FG then the batts can be held up with small wires sold for the purpose. They are slightly longer than the space between the joists and they stay there by the pointy ends sticking into the wood and they bow upwards to hold the batts in place.

   I removed all my FG and had mice, acorns, nesting material, etc falling on me. I would use foam it I insulated again. Probably use a quick spray of 3M adhesive and shove it up tight.

   Others who actually know what they are talking about should be along shortly.

1. 
   benraymond | Dec 07, 2009 11:21pm | #2

   Those mice don't eat much, do they?I was thinking spray foam. Would have to hire it out, as spraying foam while lying on my back in a dark space would be my idea of hell.

1. 
   rf_engineer_5 | Dec 13, 2009 10:58pm | #3

   I am not an expert but here is what I think you should do. I am assuming you are living in an area that gets really cold because a mostly warm area like Florida may need a different approach.

   1) You might be able to lose the FG altogether. You need to mitigate where the cold air is coming in at. Chances are it is at the rim joist. Spray foam here to take care of this. I am not talking about the great stuff cans at the store. You can buy kits online like Tiger Foam or Handi Foam. You can choose to hire it out as well. A cheaper route would be to just caulk the rim joist and seal all the way around and then use FG batting friction fitted into place. This method is not as good as spray foam IMO but if money is tight, it would suffice. Air sealing here is critical.

   2) You will need a vapor barrier on the floor. You can download some really decent articles from finehomebuilding about how to do this. It is not just putting done any old plastic. You will want to use something with low permeance. Get the articles, it will explain it. There is material called Tu-Tuff (sp?). That stuff is very good for this application. It will help keep moisture out but you have to put it down correctly. You will end up having to glue it to the wall and doing taped overlaps across the floor.

   3) You should make the crawlspace unvented all year around.

   4) You could reuse the FG batts if you want. You can buy wire hangers for this purpose. I do believe that once you mitigate where the cold air is coming in at, the FG will not be needed. The rim joist sealing and laying of the vapor barrier will help with this.

   BTW, I am doing all of this stuff myself except that my crawlspace is already sealed up.

   dennis

1. 
   Clewless1 | Dec 15, 2009 08:55am | #5

   I thought TuTuff was an air barrier e.g. like Tyvek ... in which case it would be your worst choice for a ground cover as it readily passes water vapor through it. You need to use e.g. polyethylene 6 mil minimum for a vapor retarder.

1. 
   PatchogPhil | Dec 18, 2009 02:15am | #7

   Take a read here

   http://dry-up-basement.com/vapor-barrier.html

   TuTuff is made for situations like a crawlspace. Just Google "TuTuff crawlspace".

2. 
   Clewless1 | Jan 12, 2010 09:41am | #18

   Thanks, didn't know
   Thanks, didn't know that.

   Interesting ... in classic salesman form it says ... " One of the most destructive elements that can attack a home is high moisture. It creates immediate damage like, the foul air smell, growth of mold, staining of wood, rusting of nails, saturation of insulation, etc. " I guess I don't consider e.g. mold growth, staining of wood, and rusting "immediate damage" as if this was somehow related to e.g. flooding or a tornado. If mold growth is immediate, I wonder what would a tornado be classified as.

2. 
   benraymond | Dec 19, 2009 10:55am | #9

   Thanks for all the suggestions. I definitely have decided to condition the crawlspace year round. The floor in that room (master bedroom, of course) is quite cold - I don't know yet if I want to pump warm air in there. I am thinking of either moving the deumidifier in there or putting a smaller one in.

2. 
   rjw | Dec 14, 2009 12:42am | #4

   In your climate, you want to insulate the foundation walls, put a good vapor barrier on the floor - and up the walls, if it is block (that's my opinion) close off the vents to outr doors (but leave one "loose" so air can escape - and add a vent to a supply duct in the crawl (this will slightly pressurize the crawl - in my opinion you want air from the crawl to exit the space, not find its way into the house proper)

   Forget the insulation in the floor - with a conditioned crqawl it isn't needed.

   See the buildingscience website for more info.

1. 
   Clewless1 | Dec 16, 2009 11:35pm | #6

   I have to respectfully and FULLY disagree with you. At least in part. I agree about the vapor barrier over the crawl and insulating the foundation wall (the details you left out ... e.g. what to use, how/where to apply it).

   While your approach will certainly maintain control of the moisture in the crawl, you will spend a ton of energy doing it. If you apply the vapor retarder in the crawl properly, you should not need to heat it. You certainly don't want to force heated air into it w/ an open vent!! If you want to have a truly heated crawl, you seal the perimeter/foundation well and then put a supply and a return in the crawl ... provides for a warmer floor. Also, it will pressurize the crawl with respect to the ground ... thereby resisting the tendency of 'sucking' moisture into the crawl from the ground.

1. 
   rjw | Dec 18, 2009 12:18pm | #8

   >>If you apply the vapor retarder in the crawl properly, you should not need to heat it.

   But you do need to circulate/exchange air - some vapor will work through (that's why we stopped calling them vapor barriers)

   As to heating them: I believe (but cannot prove) that a heated crawl will keep the floor warmer, keeping the occupants feet warmer, keeping the occupants feeling warming, meaning they can keep the thermostat lower.,,,

   Also, I don't think one should pull air into the house proper from the crawl space, thus, no return and a slightly leaky (not fully sealed) vent to the outside so that as the conditioned air is blown into the crawl, pressurizing it, you don't force crawl air back into the house

   As to type of insulation - I recommend unfaced fiberglass bat, preferable held 6" +/- above the floor of the crawl

   In some areas foam might be good, but I'm in termite country and have seen too many termite systems hiding behind foam panels in the crawl.

1. 
   benraymond | Dec 19, 2009 11:04am | #10

   Sorry, do you mean that I should actually insulate the FLOOR of the crawlspace? So - vapor barrier outside walls, not on the ceiling of the crawlspace, and fiberglass on the floor, and foam the outside walls?

1. 
   sisyphus | Dec 20, 2009 11:29pm | #12

   I wouldn't normally insulate
   I wouldn't normally insulate the crawlspace floor nor the crawlspace ceiling. As a previous poster suggested I would insulate the crawlspace walls (be sure to get insulation up into the joist cavities etc) and then apply vapor barrier to the floor of the crawlspace and walls (if a vapor permeable insulation is used there). If you are in an area where cooling predominates your wall VB detail may be different.

   Then condition your space and if you want to ventilate only do so when outside conditions are favorable. Typically when outside air is dry enough not to increase moisture levels in the crawlspace.

   The last crawlspace I did we put white poly tarps on the floor instead of poly sheets. The tarps reduced the humidity effectively and provided a tough surface which survived subsequent crawling better than poly does. An unexpected benefit of the white tarps was that the crawlspace is now much brighter when lit up than before.

2. 
   rjw | Dec 21, 2009 09:41am | #13

   Soory I was unclear == no insul on the floor, vapor barrier on the floor and wrapped up the walls to the sill plate (except older home with minimal exterior foundation exposure to prevent rising damp) AND insul on the walls/

   Nothing in the floor structure of the 1st floor -.

2. 
   Clewless1 | Dec 20, 2009 02:48pm | #11

   Your concepts are right. There are such things as crawlspace supply plenums; I think they used to call them plenwood systems. Better to allow a slightly leaky crawl leak to the conditioned space. Frequent air flow will minimize any moisture issues. Yeah, 'some' moisture will get through the VAPOR RETARDER, but w/ air circulation/air change, it shouldn't be much of an issue at all.

   Some energy codes require the crawl batt insulation to be in substantial contact w/ the floor, I think.

   I would NEVER consider a crawl vented to the exterior during the heating season. If you have a vapor retarder in place, you should generally have no worries. If you have a LOT of moisture, you probably should maintain a vented crawl and ensure you have to heated air forced into it.

1. 
   rjw | Dec 21, 2009 09:49am | #14

   >>Some energy codes require the crawl batt insulation to be in substantial contact w/ the floor, I think.

   I expect the code writers haven't spent much tome in actual crawl spaces.

   I've seen plenty of deteriorated insul for several inches up from various forms of flood.

   Although, come to think of it, so long as there's no paper backing, (to get moldy) so what?

   As to venting -- I don't want to vent it, I just want the air pressure from the conditioned air supply to not foerce crawl space air into the house.

   Crawls are always dirty, even nice "dry" ones. And I don't want to take a chance that if mold does grow down there (leaky pipe, bathtub overflow, etc,) ....

   Sometime, people who plan stuff forget that stuff happens sometimes, and they seem to think there won't be any problem....

   E,g,, nice "dry crawl space. House goes unoccupied for a while and the soil get saturated and high vapor results in the crawl (remember, vapor retarder, not barrier) and dome minor mold grows....

   When re-occupied, I want the air blown into the crawl to not recirculate into the house.

3. 
   tightwad | Dec 30, 2009 11:25pm | #15

   Ben -
   My 1978 house in Oregon
   Ben -

   My 1978 house in Oregon has always had cold floors in spite of the fiberglass insulation under them. Last summer I removed the underfloor insulation - and mice detritus and mummies - from below the floors in the crawlspace. Then I had a new roof put over my 100% cathedral ceiling house. This winter the floors are MUCH warmer. Of course, I close the crawl space vents in winter, and there is rigid insulation on the interior stemwalls.

   I believe that the floors are warmer because the house is not losing heat (as much) through the roof. The beautiful wooden cathedral ceilings were leaking a LOT of air through the cedar shakes. This air came in through the mud sill, below doors, etc, and made the floors cold. In the re-roof, we covered the wood decking with ice shield (100%)as an air and vapor barrier, then added 7 1/2 inches of rigid foam on top for insulation.

   The Building Science folks have it right - the house is a system. An old saying is "when your feet are cold, put a hat on". That's what we did, and it has made a huge difference. Don't look at the symptoms - look at the system. Do you see melted frost or snow on your roof in the morning before the sun warms it? Do you have icicles in the winter? If so, you probably have air leaking up through your roof, and that is pulling cold air into your home through the crawlspace.

   Before you spend a lot of time or money, get a blower door and duct test, and/or an infrared camera diagnostic. Then you'll know where to start.

4. 
   NJFoam | Jan 04, 2010 03:03pm | #16

   definitely insulate the walls to make it a conditioned crawlspace. We generally use 2" closed cell spray foam, but rigid XPS or polyiso board works too. If no one mentioned it, do a test of how much moisture is coming through the floor by securely taping down a clear poly sheet, say 2'x2' and see how much moisture accumulates underneath. If it is significant or if you have reason to believe no VB is in place, cover the floor with poly, run it a few inches up the wall, seal with mastic or foam, and install insulation, making sure to use a non-vapor permeable product. The rim joists should be sealed in well with SPF or canned foam and polyiso as well. Ditto on reading the crawlspace article on BuildingScience.com. I would also recommend the whole house testing with blower door, etc. and have the home performance contractor make some recommendations. You can always DIY.

1. 
   benraymond | Jan 12, 2010 08:37am | #17

   Thanks for all the comments. The roof, surprisingly is well insulated (although we do have a fair amount of glass in the room, so Tightwad's comments are appreciated and understood).

   My current plan is to "encapsulate," the sucker with heavy ? 20 mil plastic taped up to the walls. Slightly damp in there over the summer but nothing I think a dehumidifier won't solve - no heavy water problems.

   Then I'll insulate the walls with probably rigid foam insulation. I am going to put the fiberglass batts back, but probably won't need them much once the place is conditioned. One question about spray foam - I was gung ho about it and then I saw this site

   http://basementsolutions.blogspot.com/2009/11/do-not-spray-foam-your-crawlspace.html

   This guy suggests that spray foam will trap water against the sills and rot your house. My sills are about 2 feet above grade, while the crawl is 4 foot deep. Have you ever seen that as a problem with the spray foam?

   Thanks

   Ben

5. 
   Billy | Jan 12, 2010 11:05pm | #19

   Go to http://www.buildingscience.com and read their crawlspace insulation articles before you listen to some of the opinions here. Some of the information is good, but it's hard to filter from the misinformation.

   Yes, you want a vapor barrier on the floor of the crawl (tape the seams and seal the perimeter to the foundation walls), insulate the foundation walls and spray foam the rim joists if you can, seal all penetrations through the floor above to eliminate airflow (such as plumbing, electrical), insulate under the floor, and if you can, condition the crawlspace. Foam insulation boards attached to the bottom of the joists are great if you can get them down there.

   Here are the Building Science articles (they also have PDF versions):

   http://www.buildingscience.com/documents/information-sheets/5-thermal-control/crawlspace-insulation/?searchterm=512

   http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/?searchterm=bsi-009

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

   Billy