[Greenbuilding] Passive solar home--concrete overlay re thermalmass

[Alan Abrams]

coupla things--

1. I assumed the slab was on grade
2. I was not referring to removing insulation, I was talking about removing
the slab if it were known that there was not sufficient insulation beneath
it.

that said, if the slab is over a frame floor and it is failing, then the
first task is to diagnose the cause of failure.  Is the frame adequate to
resist deflection?  or was the failure due to the reinforcement, mixture,
and/or placement of the slab?  Or both?

if the floor is deflecting (more than, say, L/480), all bets are off, and
whatever is placed over the existing slab would be bound to fail as well.

AA

On Tue, May 14, 2013 at 8:02 AM, KTOT (g) <ktottotc at gmail.com> wrote:

>   Thank you for the comments.
>
> However, I’m not completely sure what you’re saying about insulation.
> Removing the insulation provides the opportunity to install what? There is
> a very good layer of expensive blow-in insulation under the slab, between
> the two floors, and the ceiling downstairs is finished. No way is that
> insulation coming out without destroying much of my house.
>
> The point on more mass furthering the cycle is good. The slab is already
> thicker than my designer planned for the house so already probably is
> somewhat retarded.
>
>  *From:* Alan Abrams <alan at abramsdesignbuild.com>
> *Sent:* Tuesday, May 14, 2013 5:18 AM
> *To:* Green Building <greenbuilding at lists.bioenergylists.org>
> *Subject:* Re: [Greenbuilding] Passive solar home--concrete overlay re
> thermalmass
>
>  one consideration here is that capping an existing slab in a passive
> solar system that presently works "extremely well"-- that is, adding more
> mass--is not necessarily more better.  more mass will retard the cycle of
> heating and cooling, changing the character of thermal comfort.  if the cap
> is thin enough, maybe it won't be noticed--but this is all quantifiable.
>
> it all raises many questions--about the climate, about the substrate under
> the slab, about the details of the envelope of the house--all factors that
> come into play in this decision.  maybe there is not much insulation under
> the slab, so that removing it provides the opportunity to install it.  if
> there is adequate insulation under the slab, then maybe a thin cap is in
> order.
>
> on the subject of thermal mass and heat transfer, I think RT's earlier
> reply was definitive.  thermal mass is simply a function of density or
> specific gravity, and an acrylic admixture and/or thin film of bonding
> compound between original and new slabs would neither change the density of
> the slab or retard conductive heat exchange between the two in any
> significant way.
>
> some time ago on this list serve, back in the pleistocene era, IIRC, there
> was a discussion on high strength, super thin slabs, akin to ferro-cement
> boat hulls--which might have application here.  someone with even more time
> than I have to waste could look it up.
>
> AA
>
> Alan Abrams*
> **certified professional building designer, AIBD
> certified passive house consultant, PHIUS*
> *certified passive house builder, PHIUS**
> *Abrams Design Build LLC
> *sustainable design for intentional living*
> 6411 Orchard Avenue Suite 102
> Takoma Park, MD 20912
> office  301-270-NET- ZERO (301-270-6380)
> fax      301-270-1466
> cell     202-437-8583
> alan at abramsdesignbuild.com
> www.abramsdesignbuild.com
>
>
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