[Greenbuilding] insulating beneath an existing floor.

[Sacie Lambertson]

Thanks for the so-far responses to my query (John and Bob).  To clarify the
problem:

The house is sitting on top of the stone wall foundation so there is a
space between the floor and the ground.  Presume (because the house won't
be gutted for a year or more) the yellow pine floor rests on joists.  There
is no access to the space underneath, short of tearing up the floor.  This
seems to me entirely unnecessary given those boards have been there for
over 130 years.

I mentioned the old limestone wall only because I think placing insulation
against the wall as might be normally recommended, is not a good idea given
the potential for the limestone to deteriorate when it is thus enclosed.
We have a good friend who is a master stonemason whose opinion I will ask
about this problem.  Also will ask him to check out the existing wall which
will need repointing IMO.  Have no idea what material has been used to
point up until now.  Will check on this again.

I'm thinking someone will have to crawl through some access point into the
crawlspace of the floor and with good light insulate the floor from
underneath, presumably a spray foam.  I think this is what you are
suggesting Bob.  Further, your assessment of the situation is sound me
thinks.  Wonder if putting vents in the wall would assure an air flow?
Necessary?  There are none now.  The limestone wall around the main house
is in very good shape.

Assume without knowing, the floor joists are fairly deep given the rooms'
dimensions (@14' x 14'-a bit over 1000 sq ft total).   So if only the
joists were enclosed in foam, the space beneath would be left as is--ie
open dirt surrounded by limestone walls.

The lot is flat flat.  There is no indication of water damage around the
perimeter except in the back where the lot actually slopes toward the house
and where the foundation to the  addition is failing (added about 100 years
ago on top of a similar limestone wall).

The addition and wall will be demolished.  There is a small rudimentary
basement under the addition.  A proper small basement will be built under a
new addition and a good french drain will be placed in the yard behind it
(the slope can not be changed).

Further responses valued.  Sacie

On Thu, Jul 30, 2015 at 9:05 AM, home-nrg <home-nrg at dnaco.net> wrote:

> Sacie,
>
> Without more info on your earlier experience, and in view of
> how limestone is subject to erosion by water contact as well
> as the freeze/thaw cycle, protecting the foundation would
> seem to be essentially isolating it from moisture in any
> form.
> The airflow of an exposed, unsealed foundation traditionally
> provided this.
>
> The measures for reducing structural heat loss is likely to
> change the conditions which drove that airflow
> (ventilation).
>
> Presumably the "floor" inside the foundation is ground (soil
> or gravel) without a moisture barrier seal. This leaves that
> soil as a moisture source in most parts of the country.
>
> What sort of provision have you made for perimeter drainage?
>
> From what you describe, I'd suggest you consider treating
> the floor as a sixth exterior wall, with suitable insulation
> and air sealing.
>
> An alternative to a compulsively complete, fully sealed
> over-soil moisture barrier would be a dedicated fan to
> pressurize the enclosed (crawl) space, to provide the force
> for air flow through the foundation.
>
>  (Find something more durable than construction-standard
> 6-mil plastic. Clients have had good luck with 10-12mil
> commercial membrane.)
>
> Just my speculation, without seeing the site or having more
> information (and not having to fund the work).
>
> Bob Klahn
>
> ----- Original Message Follows -----
> From: Sacie Lambertson <sacie.lambertson at gmail.com>
> Subject: [Greenbuilding] insulating beneath an existing
> floor.
> Date: Wed, 29 Jul 2015 22:58:45 -0500
>
> > What is the best way to insulate the floors of an old
> > house that sits on a 30 inch limestone foundation wall?
> > The wall, solid since 1883, needs to continue to
> > 'breathe'.  Limestone such as is used for the foundation
> > is similar to that used in old barns; the stone will last
> > a very long time as long as it does not have dirt behind
> > it, ie as long as it is free standing.  We've had personal
> > experience with this when we used old barn foundation
> > stone to build rock walls behind which is dirt.  They
> > began to deteriorate relatively fast.
> >
> > Most of the interior of the old house will be nearly
> > gutted, leaving only the the exterior siding, which is
> > also original amazingly enough, as is essentially the
> > interior.  The old yellow pine floors will be retained but
> > must be insulated underneath.
> >
> > The house will be reconstructed with double passiv haus
> > type walls.
> >
> > Thanks for your advice,  Sacie
> >
> >
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