Insulation question

Coach606 · Oct 20, 2007

The previous owners of my house turned the three season porch into an all season porch. Unfortunately, there is no insulation under the maple flooring. underneath the floor is a stairway from the walkout basement. Every winter the floor feels ice cold and that area of the house won't stay heated very well.

I'd like to go outside and put some kind of insulation under the floor. I was thinking of that gap filler spray foam, but I have to stand under the floor and spray up. The foam won't stick and it'd be pretty time consuming.

Any suggestions for how to get this done? Thanks.

Jadnashua · Oct 20, 2007

The small spray cans of foam would be really costly to fill that area. There are larger 2-part systems you can buy in larger containers that comes out more liquid than a stickier paste. I've never used it, but have seen it advertised. the alternative, and I don't know if between the setup charge (which is probably a constant amount) verses the relatively small area to be insulated would make having it done cost effective. What I mean by that, is that they probably charge some flat fee for just showing up which takes into account setup, then cleanup. That charge would be the same regardless of whether they sprayed 10 sq ft or 1000 sq ft. Then there'd be a fee for the amount of area to be covered. If you had some other areas of the house that could benefit from the added foam insulation, it becomes more ecconomical.

Sponsor · 2022-01-29T12:20:58-0800

Coach606 · Oct 20, 2007

batt insulation

What about just buying some batt insulation and tacking it on with nails in the space between the studs? That stuff is okay outdoors, right? Again, this is under a porch so it's not going to get direct weather.

I researched a few of the 2 part systems. Their pretty expensive as well. But thanks for that recommendation.

Jadnashua · Oct 20, 2007

You'll need a vapor barrier at the house side of the insulation. You can buy special clips to hold insulation up in a bay. Batt insluation is a good invitation to critters to nest in. If you used that, you might want to put something up over it. this would also help prevent air flow...fiberglass acts more like an air filter (think furnace) than insulation if it is out hanging in the wind.

Geniescience · Oct 21, 2007

how much headroom is there underneath?

david

Brownizs · Oct 21, 2007

Once you put the Insulation up, you will need to cover the bottom of the porch with paneling rated for Exterior (possible vents in it to allow for some breathing).

Leejosepho · Oct 22, 2007

I have a similar situation where I had to "indent" a foundation wall to keep it far enough away from the well to allow for any future termite treatment. So, now I have a 3'x10' area --\_/-- over which a framed floor will be placed. My plan is to insulate that area with fibreglass batts between the joists and to then cover the bottom with plastic lattice (for ventilation) that has window-screen material attached (to keep bugs out).

Does that sound okay?

Jadnashua · Oct 22, 2007

Fiberglass depends on relatively still air to function. I'm not sure how effective it would be where it was open to the outside.

Frenchie · Oct 22, 2007

Coach, Lee -

Under the FG in your floor cavity, you need something that will stop air movement. Otherwise, you may as well not bother insulating: air infiltration will completely defeat any insulative qualities the FG has to offer.

Housewrap, at a bare minimum. 1/2" ply, screwed into the joist bottoms (covering the housewrap), better. All penetrations sealed & all seams taped, of course...

The two-part foam is pricey, but once you figure in the labour costs of installing the bats & an air infiltration barrier, it's not such a bad deal.

Jadnashua - You don't need a separate vapor retarder, in this case. The subfloor (assuming it's plywood or OSB) will act as such.

Leejosepho · Oct 22, 2007

frenchie said:
Under the FG in your floor cavity, you need something that will stop air movement. Otherwise, you may as well not bother insulating: air infiltration will completely defeat any insulative qualities the FG has to offer.

Housewrap, at a bare minimum. 1/2" ply, screwed into the joist bottoms (covering the housewrap), better. All penetrations sealed & all seams taped, of course...

So then, no need for any ventilation? The bottom of this will be a foot off the ground and on the north side of the house (always in the shade) between Detroit and Chicago.

Frenchie · Oct 22, 2007

Do you ventilate walls? This isn't a roof, bro, you don't need to worry about ice dams.

That's pretty close to the ground, and if you can dig down a bit, you should. But also, more importantly, make sure you have some kind of vapor barrier on the ground beneath it (6 mil poly is typical). The average crawlspace puts out 11 gallons of water a day (!!).

Are there any moisture issue at ground level? If not, you might want to consider a sealed crawl. The detailing is a lot more critical & demanding, but it uses less insulation, and gives better results. Code approval can be a hassle, though.

Leejosepho · Oct 22, 2007

frenchie said:
Do you ventilate walls? This isn't a roof, bro, you don't need to worry about ice dams.

Sure. My concern here is the possibility of mildew, mold or rot.

frenchie said:
That's pretty close to the ground, and if you can dig down a bit, you should. But also, more importantly, make sure you have some kind of vapor barrier on the ground beneath it (6 mil poly is typical).

Going down another foot and placing rocks on top of poly would not be a problem.

frenchie said:
Are there any moisture issue at ground level? If not, you might want to consider a sealed crawl ...

The wall at the opening of this area is three feet back from the two-story roof edge above, but the pine trees about thirty feet away would not keep a northeaster from blowing rain or snow into it. And to keep this from becoming a critter den, the 2'x'10' opening will at least be covered with the lattice and screen I had mentioned earlier.

Frenchie · Oct 25, 2007

You might want to consider a sealed crawlspace, then: where you enclose the & insulate the perimeter, instead of leaving it open.

Less materials, easier install, better results.

Google it, there's a lot of good info out there. Here's a few documents I had bookmarked:

http://eber.ed.ornl.gov/Residential_Products/DOE crawlspace 774 .pdf

http://www.buildingscience.com/docu...rawl-space-construction-performance-and-codes

Insulation question

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