SB: Re: Re: Bales in Floor

["S. G. Fawthrop" <S.G.Fawthrop@Eklectika.net>]

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