Crawlspace under addition


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Old 10-17-15, 08:00 PM
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Crawlspace under addition

I've got an addition with open-sided dirt floor crawlspace on my house that had fiberglass insulation installed upside down and stapled to the joists through the paper. It had almost all collapsed and served as a nice home for some critters last winter, so I took it all out last weekend. Clearance underneath varies from just a few inches in one corner to about 2.5' in the opposite corner. I don't think enclosing is feasible for the amount of money/interest I have for this project. From reading other posts/links on similar situations, it sounds like the main options are spray foam or to use rigid foam boards underneath the joists with fiberglass in the bays. A couple of questions on these options: is this a good candidate for a DIY Tigerfoam or similar installation? If I went the rigid foam route, is 1/2" thickness mounted to the bottom of the joists good enough for MD temperatures? I'm guessing a vapor barrier on the ground is also recommended for this application? I'll take some photos tomorrow and post them.
 
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Old 10-17-15, 11:05 PM
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Not even close to enough.
Recommended Levels of Insulation : ENERGY STAR
And what's going to stop them from chewing right through it?
 
  #3  
Old 10-18-15, 05:37 AM
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I was planning on hardware cloth or chicken wire around the base for the critters, for the foam my goal is to keep the fiberglass/joists just warm enough to not build up moisture. Joists are 2x8, so should be able to fit R19 or so in there, and I guess stepping up the foam to 1" would give R25.

This addition was built in '99, and it appears with shortcuts taken in construction, so I'm guessing the insulation in the walls/ceiling is suboptimal. Does it still make sense to go all the way to the recommended R25 in the floor when I don't have access to get in the walls or attic to beef that up? The addition does not have a duct from the house's HVAC, it's got electric baseboard heating. There is a sliding glass door separating the addition from the house, which I kept closed last winter. There were some pretty bad windows that had failed seals, but they've been replaced now. Ideally I'd like to keep that door open this winter to get more use out of the space without driving heating costs up too much.
 
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Old 10-18-15, 06:08 AM
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A couple of points that may help.
1. The minimum code levels are just that, a bare minimum. More is always better.
2. Air infiltration starts at the floor level so air sealing is more important than extra insulation. That means the bottom layer should be really good, sealed all the way around and all seams sealed.
3. Floors are the hardest areas to heat as the warm air gets pushed up and the cold air collects down low.
4. Having worked on a few additions over open spaces, pay special attention to any place where critters can get in.

Bud
 
 

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