[Greenbuilding] insulating beneath an existing floor.

[home-nrg]

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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