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'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.
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'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.
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
If you could put up with 3/4 foam plus at least 1/2 plywood, I think it
Fiberglas is the cheapest for its r value, so if you can insulate from
below, fiberglas will be the least expensive.
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.
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'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'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.
How about 1" foam, 3/4" plywood, and 3/4" hardwood floor? I'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'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.
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. .
Everyone, thanks---that super beefy floor is going to be a problem---that
would put me seriously over the surrounding floors and we'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.
wrote in message
The bigger question here is why bother at all? You have a full
basement underneath. None of the homes I've lived in nor any of the
new construction I'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.
I'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've never had it and don'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.
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