Insulating Floor Above Crawl Space

[BikingBrian]

I'm thinking about insulating the floor above my crawl space, has anyone done that?  I know there's as much benefit as well insulated walls and attic (which I already have insulated), but it would be nice not to have my new tile floors being cold in the winter.  My only concern is freezing pipes under the house - any problems with that after insulating the floor?

I know insulating crawl space walls instead of the floor can be done, but I believe that is not an option for me as my crawl space is vented and I need combustion air for my floor furnace.

[Chesslike]

Yes I have done that and your pipes will be fine as long as you have some type of insulation on them as well, which you should anyway.

I also just read that its a good idea to place Tyvek under there as well, not only does it help keep the insulation in place it prevents drafts, which makes your living space more comfortable. I plan on doing that the next time I have some work to do under the house.

[MountainGrizzly]

I have had great success in comfort and lowered heating cost with this method.

My house was built in 1967.  It had a simple plywood subfloor covered with linoleum.  In the winter, the air only 1 1/2" below my toes was 30 degrees.  The temperature at the floor was about 60 degrees, when the central heat was at 69.  After insulating the crawlspace under the floor, the tile is about 67 degrees.

Since most of the pipes run under this, I insulated the pipes.  There is enough heat leakage that my pipes have never frozen.

[Up Sheep Creek]

What did you use and how did you do it.  I had some extra roll type insulation and used it under the house but it does not stay up very well.  Did you staple it, cram it in place or use the wire?  Any tips?

[BikingBrian]

I haven't done it yet, but at Mt Hardware I found the wires ("lightning rods") that you push between the floor joists to hold the insulation in.

[Up Sheep Creek]

Those wires come in different lengths.  Learned the hard way when I thought I could just cut them down to fit. The tyvek over the insulation might be the way to go.

[MountainGrizzly]

What did you use and how did you do it.  I had some extra roll type insulation and used it under the house but it does not stay up very well.  Did you staple it, cram it in place or use the wire?  Any tips?

I used Kraft-Faced 16" wide bats, which I stapled to the subfloor.  The insulation is left hanging from the Kraft Paper.  It does droop, so the follow up is Tyvac or plastic sheeting.  I just make sure the sheeting isn't too perfectly air tight.  Some small gaps help it breathe.

[BikingBrian]

Do you have the vapor barrier (paper) on the top or the bottom?  Everything I've read says it needs to be on top.

[MountainGrizzly]

Yes, the Kraft Paper Vapor Barrier is at the top, against the subfloor.  I wound up flexing the paper around so the wings hung down the sides, and stapled the wings to the floor joists.

Then the insulation droops below that (it holds in place for a month or two), then below that the plastic sheeting (Tyveck would be best, but I used clear, with a few holes poked here and there).

[BikingBrian]

Oh, I see, the insulation holds on long enough for you to put the plastic underneath...

[Up Sheep Creek]

Oh poop!  I installed the insulation with the barrier down not up against the subfloor.  Easy fix since I used the wires.  The Johns Manville website has a video that shows how to insulate a crawlspace.  Very helpful.

[MountainGrizzly]

Oh, I see, the insulation holds on long enough for you to put the plastic underneath...

Unless you get tired and leave it for 2-3 months.  Then its drooping.

[K9luvr]

I did this to my house in Indiana when I lived there.  I also had the folks I hired to do the labor wrap the pipes while down there.  It made a HUGE difference in my heating needs (I heated with wood and had a backup electric furnace for when I was gone for long periods). No more having to get up in the middle of the night to stoke the woodstove to keep from waking up in a cold house!  I think you will really enjoy the results.