[Greenbuilding] R-value of crushed stone under slab

Tue Dec 8 00:13:58 CST 2015

With vertical insulation encasing the rock you would benefit from the deeper soil temperatures as well as the rock mass would take on the temperature of the deeper soil and you could model that - but one concern that I would want to consider is groundwater pressure (finding a nice big pool to fill) though that shouldn’t really affect temperature unless the seepage is closer to surface soil temperatures.

From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Alan Abrams
Sent: December-07-15 4:24 PM
To: Green Building
Subject: Re: [Greenbuilding] R-value of crushed stone under slab

Frank, the stone was under 9" of geo foam @ R-4.2, supporting a 4" slab.. 

still, according to PHPP, there is a lot of impact to the gross modeled result from decoupling the assembly from the subsoil. FWIW, the gravel fill was also encased in vertical 

insulation. So the R-value of the stone may not be trivial...

-aa

Alan Abrams
certified professional building designer, AIBD
certified passive house consultant, PHIUS

certified passive house builder, PHIUS
cell     202-437-8583
 <mailto:alan at abramsdesignbuild.com> alan at abramsdesignbuild.com
HELICON WORKS  <http://www.heliconworks.com/index2.html> Achitecture and Education

On Mon, Dec 7, 2015 at 7:03 PM, Frank Tettemer <frank at livingsol.com> wrote:

I would consider the 24" of gravel as a steady, 24/7 heat loss.  In fact, in a colder climate, (like Eastern Ontario, Canada), there would be little consideration of trying to heat that gravel. Any heat going into it from the house would continue traveling down and out, and the heat added to the stone would never return to the house. Unless you opened all the windowsand doors to quickly chill the place. Then for a short while, the cool stones would give offtheir relative heat to the room.

In other words, dee-coupling from the stones, with at least R-25 insulation, would be a Good Idea.  If you were a Passiv Haus enthusiast, you would insulate with R-45 or more, to prevent heat loss to those stones.

Frank Tettemer
Living Sol ~ Building and Design
www.livingsol.com
613 756 3884

On 07/12/2015 5:26 PM, Norbert Senf wrote:

Right, I was only addressing the "heat capacity expressed as MJ(m^3K)" part of the question. R value of gravel is a look-up value............N

On Mon, Dec 7, 2015 at 2:42 PM, Nick Pine <nick_pine at verizon.net <mailto:nick_pine at verizon.net>> wrote:

    Norbert Senf <norbert.senf at gmail.com
    <mailto:norbert.senf at gmail.com>> writes:

        ... the specific heat would be .14 MJ/m3-K

    I'm afraid that has nothing to do with R-value.

    Nick

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Norbert Senf
Masonry Stove Builders
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