SB: Re:bales in ceiling was Bales in Floor

["Aaron Corbin" <aaronc@frontiernet.net>]

    One concern with metal roofs is that they condense moisture that can
drip onto the bales. I would deal with this by making sure the attic space
is well ventilated and the straw in the attic is covered in a clay slip. I
believe covering the straw in the attic with some kind of plaster is very
important and often gets over looked. Plastering provides a flame resistance
as well as increasing the R-value. As far as creating a vapor barrier on the
ceiling, I would think twice. Unlike fiberglass, straw has the ability to
let moisture migrate through it. I say let it move. If we vapor barrier the
ceiling that's all the more vapor that will be moving through the walls.
Aaron Corbin
Viroqua, WI

 > Well, if bales in the floor are not such a good idea, what about bales in
> the roof?  Obviously a vapor barrier is needed, but there are any other
> problems with putting bales under a metal roof?
>
> Steve
>
> ----- Original Message -----
> From: "Robert W. Tom" <archilogic@yahoo.ca>
> To: <strawbale@crest.org>
> Cc: <S.G.Fawthrop@Eklectika.net>
> Sent: Monday, December 17, 2001 6:30 PM
> Subject: SB: Re: Bales in Floor
>
>
> > 12/17/01 10:33:46 AM, "S. G. Fawthrop" <S.G.Fawthrop@Eklectika.net>
wrote:
> > [snipped & pasted]
> > >3" concrete on 3" gravel as a base.
> > >2-string bales separated by 4" in each direction.
> > >3" concrete on top.
> > >based on a ground temperature of between 45 and 50 degrees it seems
> > >to me that the bales would help reduce heat loss considerably and
> > >the extra expense (estimated at about $3/sf) may be worth it.
> >
> > > I am located in the mountains of south-west
> > >Virginia at an altitude of about 2800ft.
> >
> >
> > Steve;
> >
> > If yours is a predominantly-heating climate, then for comfort's sake
> > it probably would be "worth it" to decouple the slab from the earth.
> >
> > As to whether there would be a reasonable payback period, it would
> > depend upon some specific variables related to your situation
> >  (ie HDD/yr, fuel costs (present & future) etc) , information which
> > I don't have.
> >
> > But using a bale-insulated waffle slab as an insulation strategy
> > is IMO, highly questionable at best and potentially disastrous at worst.
> >
> > First of all, the concrete webs between the bales represent thermal
> > bridges which will compromise the effective thermal resistance of the
> > floor assembly ( thermal conductivity of normal density 2400 kg/m^3
> > concrete  = 1.4 to 2.9 W/m*degC  which translates to R-0.05 to 0.1 per
> > inch) .
> >
> > A quick number-crunch tells me that the effective R-value
> > for the slab as per your specs, would be about  R-4.4,
> > (optimistically assuming an ideal , in-lab R-value of  R-46 for
> > very dry straw and straw  density of ~12 lbs/ft^3,  reasonable
> > since the bales will be compressed )
> >
> > Yup, that was  R-four-point- four, average overall R-value for the slab
> > assembly when one takes the concrete webs into account .
> > That's a little bit less than what an inch of XPS  or 1.5" of EPS
> > or Roxul would yield.  Other gearheads may want to check
> > the arithmetic but I'm pretty sure that it's correct.
> >
> > Then there's all that concrete that's consumed in the 4-inch wide
> > "ribs" between the bales.
> >
> > In a floor measuring 6 bales by 6 bales, there would be
> > 2.6 cu yards (ie 70.2 cu ft) of concrete just in the webs
> > and that's not counting the concrete that would be at
> > the perimeter, which would likely be there anyway, in a stem
> > wall design.
> >
> > So the concrete in the largely redundant webs alone consumes
> > more concrete than  the entire 3" thick floor.  That doesn't seem
> > like a very effective use of a high embodied energy material to me.
> > If one were to design a concrete beam or pile supported suspended
> > slab my off-the-cuff guesstimate would be that the amount of
> > concrete consumed could be reduced by 75%.
> >
> >
> > Then there's the issue of the longevity of the straw.
> >
> > With a waffle slab, one is essentially creating a vapour-impermeable
> > bell jar to trap moisture in the straw .  A CMHC study a year or two
> > ago confirmed what one suspects would happen in such a scenario
> > ... rotten straw.
> >
> > And what if your design is such that you wanted to have plumbing
> > and heating paraphernalia requiring water-carrying pipes
> > beneath the floor surface ?  This is the stuff of SB nightmares.
> >
> > Would I build a SB-insulated waffle slab ?
> > Only if I had a bunch of concrete that I wanted to waste and if I didn't
> > care how poorly-insulated the slab would be and if I wanted to
> > create an unhealthy environment seething with Fetid Black Goo.
> >
> > Moral of the story: There are better ways to create an insulated slab.
> >
> > --- * ---
> > Rob Tom
> > Kanata, Ontario, Canada
> > <ChaffArchiLogic@yahoo.ca>
> > (winnow the "chaff" spamguard from my edress in your reply)
> >
> > Please visit http://www.theHungerSite.com daily
> >
> >
> >
> >
> >
> > _________________________________________________________
> > Do You Yahoo!?
> > Get your free @yahoo.com address at http://mail.yahoo.com
> >
> >
>
> -------------------------------------------------------------------------
> > To unsubscribe from the list, send a message to:
> >    <strawbale-unsubscribe@crest.org>
> >
> > or for the digest to:
> >    <strawbale-digest-unsubscribe@crest.org>
> >
> > Please send any list administration questions to
> > strawbale-owner@crest.org
> >
> >
>
>
> -------------------------------------------------------------------------
> To unsubscribe from the list, send a message to:
>    <strawbale-unsubscribe@crest.org>
>
> or for the digest to:
>    <strawbale-digest-unsubscribe@crest.org>
>
> Please send any list administration questions to
> strawbale-owner@crest.org
>
>


-------------------------------------------------------------------------
To unsubscribe from the list, send a message to:
   <strawbale-unsubscribe@crest.org>

or for the digest to:
   <strawbale-digest-unsubscribe@crest.org>

Please send any list administration questions to
strawbale-owner@crest.org