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Insulated floors?

Anybody else have wood floors with a crawl space underneath? As the weather turns cold I'm increasingly noticing the fact that there's simply two layers of cross-sectional wood separating me from 50 degree air. Has anybody with a similar flooring situation insulted underneath? Did it help? Any problems?

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Permalink Reply by jeff on October 8, 2009 at 1:01pm: done all the time.
for reference, the city's energy code for new construction requires R21, which is a 5-1/2" standard density batt. unfortunately, batts don't help much with the energy loss because of airflow, which is a real problem for a floor over crawlspace. spray-foam works much better, but it's more expensive.
since you're a d.i.y. guy, you could get under there and use cans' of spray foam to seal openings, etc., followed by kraft-faced batts. be sure to tape the joints.; ▶ Reply to This

Permalink Reply by Brendan on October 8, 2009 at 1:22pm: What sort of airflow is going on that renders batts ineffective? I figured that's what they were there to stop ;-) Also, since my joists are 2x8 (possibly 2x10) I'm wondering if that gap between the subfloor and the batt is an issue. Would rather not use spray foam generally as it's a little trickier to "undo" than pulling out some staples.

That's a lot of spray foam, too. A coworker in NH, when building his house, used two 55 gallon barrels of the stuff. Yikes.; ▶ Reply to This

Permalink Reply by ramon t on October 8, 2009 at 1:49pm: Assuming your crawlspace is Ventilated.

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Insulating a Ventilated Crawl Space
Here are some guidelines to follow for insulating a ventilated crawl space:

Carefully seal any and all holes in the floor above ("ceiling" of the crawl space) to prevent air from blowing up into the house.

Insulate between the floor joists with rolled fiberglass. Install it tight against the subfloor. Seal all of the seams carefully to keep wind from blowing into the insulation. Also, adequately support the insulation with mechanical fasteners so that it will not fall out of the joist spaces in the years to come. DO NOT just rely on the friction between the fiberglass and wood joists to secure it in place.

Cover the insulation with a house-wrap or face it with a vapor barrier. The orientation of the vapor barriers depends on the home's location or climate. In most of the country, the vapor barrier should face upward. However, in certain regions of the Gulf states and other areas with mild winters and hot summers, it should face downward.

Install a polyethylene vapor retarder, or equivalent material, over the dirt floor. Tape and seal all seams carefully. You may also cover the polyethylene with a thin layer of sand or concrete to protect it from damage. Do not cover the plastic with anything that could make holes in it, such as crushed gravel. Be sure the headroom of the crawl space meets local code regulations if you are considering pouring a concrete slab.

http://www.energysavers.gov/your_home/insulation_airsealing/index.c...; ▶ Reply to This

Permalink Reply by Brendan on October 8, 2009 at 1:56pm: Thanks! The stuff I've seen previously was all for unventilated spaces and consequently looked silly ("Why would I insulate the foundation when there's intentional vents to the outside?").; ▶ Reply to This

Permalink Reply by Talia Freedman on October 8, 2009 at 3:38pm: I'm on a slab, but another option besides the rolled batting seems to be polystyrene. You can cut it to fit between your joists and it seems a lot neater than fiberglass. Also, doesn't need netting to keep it in place.

Good luck with it. Every bit helps with energy costs.; ▶ Reply to This

Permalink Reply by jeff on October 8, 2009 at 5:08pm: that's good info from .gov, except in our climate, a vapor retarder on the dirt isn't necessary. we almost always have higher vapor pressure insides our buildings than outside.
of course, it does make the crawlspace nice and clean and makes it easy to notice if anything has been down there like animals, leaks, flooding, etc.; ▶ Reply to This

Permalink Reply by Tiefa on October 10, 2009 at 7:23pm: I have a floor situation just like yours. When I had pros come in to insulate the attic, I asked them about insulating the floor.
They said to use batting, that vapor barrier must be toward heat source and that it really doesn't help that much with the energy bills.; ▶ Reply to This