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

[KTOT (g)]

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 
Sent: Tuesday, May 14, 2013 5:18 AM
To: Green Building 
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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