insulating subfloor

[<bks>]

I am looking to add insulation to a first room floor (100-year-old farmhouse, full fieldstone basement underneath). Will be removing carpert and pad (about an 1"), putting down laminate flooring, so have some room for a layer of insulation.a

Is it possible to put a layer of foam board below a 1/4" layer of ply prior to flooring? The basement is a rat&#39;s nest of wires and pipes. Maybe even a simple layer of poly would make a huge difference?

FYI: I have already done the walls and sealed all cracked in them and around pipes. New windows, etc. This is the last frontier.

Thanks.

[m Ransley]

Insulate from the basement I wouldnt use anything under the subfloor, foamboard under the subfloor will have about as much affect as carpet and pad does now and be soft and compress, bad idea.

[Edwin Pawlowski]

Some materials are referee to as "rigid" insulation, but they are not rigid enough. Not a good idea as they will compress over time and cause problems with soft spots and flexing.

[Buck Turgidson]

It is not cheap, but you can buy the spray on kind of foam, and spray from underneath. That might help with your "rats nest."

[Joseph Meehan]

No, go the proper way and insulate from underneath.

I have one caution however. You say you have pipes in the basement. Assuming some of those pipes carry water, I suggest that you make sure you don&#39;t insulate so much as to allow some parts of your basement to go below freezing on the coldest of days anywhere near any of those pipes.

[m Ransley]

Maybe look at basement walls first, then basement ceiling and as JM said remember about the pipes.. Thick foam pad and carpet do alot.

[yourname]

If the space underneath is not high enough, they will not be able to spray foam properly[see my older thread]

I have 2 inches of foam under my concrete garage floor, why not under a house floor?

If you could put up with 3/4 foam plus at least 1/2 plywood, I think it would work

Fiberglas is the cheapest for its r value, so if you can insulate from below, fiberglas will be the least expensive.

[Joseph Meehan]

Too hard to work with and too expensive and if you enclose wires or pipes, too hard to access them. Also make sure you are using a foam rated for the use as some are fire hazards.

Other than that foam can be an outstanding insulation.

[Edwin Pawlowski]

You THINK it would work??? Not much confidence there.

The 2" of foam you have is under a 4" thick slab of concrete with re-bar or wire screen keeping it all together.

That is much different than foam under laminate. The laminate is about 1/4" to 3/8" thick and will flex considerably after the foam starts to compress over time. If there is enough room for buildup of the floor, you&#39;d want at least a 3/4" plywood underlayment over the foam.

If it is eps foam, it can support about 20 psi with minimal deflection. The laminate will flex but I don&#39;t have figures for it. Take a 200 pound person putting down a heel on the floor and what is the psi loading of that point? Repeat this many times a day for years.

[Wayne Whitney]

How about 1" foam, 3/4" plywood, and 3/4" hardwood floor? I&#39;m thinking one reason the foam under 4" thick concrete slab works is that the concrete slab will disperse a point load over a 4" radius circle of the foam. (Isn&#39;t that loads work, they fan out at 45 degrees?) With 1.5" of wood, it will only fan out over 1.5" radius circle, I wonder if that is enough.

Cheers, Wayne

[Edwin Pawlowski]

That would be a rather beefy floor and would probably work very well. Only problem I see is that the floor is suddenly 2 1/2" thicker and may cause problems with any built in fixtures or a step at the top of the stairs. There is a code on how much any step can vary in a set. .

[<bks>]

Everyone, thanks---that super beefy floor is going to be a problem---that would put me seriously over the surrounding floors and we&#39;re a clumsy family :)

Looks like the way to go is probably some insulations underneath, insulation on all the pipes in the basement to help prevent freezing. Thanks.

[trader4]

The bigger question here is why bother at all? You have a full basement underneath. None of the homes I&#39;ve lived in nor any of the new construction I&#39;ve seen has insulation under the living space floor above a full basement, unless they are using radiant heat. I think the reason is the temp delta between the living space and basement, which is surrounded by earth, is not great enough for it to make that much difference beyond the insulating value of the subfloor, floor, etc.

[Edwin Pawlowski]

I&#39;ve seen a few new houses built with insulation on the floor. My neighbor had to add insulation before his house could be approved for a mortgage. I think it was FHA or something that required it. New house across the street from me has it also. Like you, I&#39;ve never had it and don&#39;t really see much need as the basement has to be kept at least above freezing, maybe more if you use it on a regular basis.

[yourname]

The reason would bew that since ther is no insulation around the foundation, ther eis no inulation period. Just becaase the floor doesn&#39;t feel cold, doesn&#39;t mean you are not losing heat.