[Greenbuilding] insulating beneath an existing floor.

[home-nrg]

Sacie,

re: foundation vents.
Unless there is a driving force to move air through them,
i.e. a fan or supply vent to pressurize the space under the
house, or a wind -at ground level (unlikely in most areas),
foundation vents do not & never have worked as intended. 
The idea behind them relies on flawed science.
Save the money to use productively elsewhere. 

Bob Klahn

----- Original Message Follows -----
From: Sacie Lambertson <sacie.lambertson at gmail.com>
To: Green Building <greenbuilding at lists.bioenergylists.org>
Subject: Re: [Greenbuilding] insulating beneath an existing
floor.
Date: Thu, 30 Jul 2015 11:59:29 -0500

> 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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