[Greenbuilding] R-value of crushed stone under slab

Tue Dec 8 10:24:49 CST 2015

on the other hand, if the perimeter insulation runs lower than the fill
(it's around 4' from footing to top of slab), and if the R-value of the
fill is negligible, then the assembly is not completely decoupled.

all that aside, the notion that PHIUS "is making large amounts of
insulation socially acceptable" is making my head throb...at last, I can go
out in public again...

Alan Abrams

*certified professional building designer, AIBDcertified passive house
consultant, PHIUS*
*certified passive house builder, PHIUS*
cell     202-437-8583
alan at abramsdesignbuild.com
HELICON WORKS *Architecture and Education*
<http://www.heliconworks.com/index2.html>

On Tue, Dec 8, 2015 at 11:06 AM, John Salmen <terrain at shaw.ca> wrote:

> Decoupling the model from the slab removes it from an assumed heat source.
> Leave it coupled but add the 24” of gravel as a low value underslab
> insulation below the foam.
>
>
>
> Insulation curves start to flatten after 4” – in Ontario during the 90’s
> they actually were looking at reinstating r12 as an acceptable wall
> standard for that reason. Flattens more dramatically after 6”. I think one
> of the benefits of PHIUS is that it is making large amounts of insulation
> socially acceptable in the building community. The reality is that there is
> a great deal of conflict between size of house, insulation levels,
> ventilation requirements and heat recovery efficiency.
>
>
>
> I think if you accept the concept that there is no such thing as free
> energy – any energy savings is going to result in a transfer of energy
> somewhere else – utilization of some equivalent material at some point in
> the process.  E=mc2 type of thing. Even solar energy is not free as it is
> simply being redirected.
>
>
>
> *From:* Greenbuilding [mailto:
> greenbuilding-bounces at lists.bioenergylists.org] *On Behalf Of *Alan Abrams
> *Sent:* December-08-15 2:14 AM
> *To:* Green Building
> *Subject:* Re: [Greenbuilding] R-value of crushed stone under slab
>
>
>
> 23.8  Table 3A, for "Sand and gravel or stone aggregate of 140 pcf
> density" it lists its thermal resistivity (ie  R-value per inch thickness)
> as being:
>
>
>
>                   (oven dried)  0.11     and   (not dried)   0.08    in
> units of   h*ft^2*degF/Btu
>
>
>
> thanks, that same citation is included in the AGS, but methinks that it
> refers to a solid, compacted mass of sand AND gravel, whereas the condition
> in question is washed, crushed stone, occupying maybe 60-70% of the volume,
> and the remainder being air. I would also assume there would be less
> conductivity between the stones than in sand and gravel.
>
>
>
> the notion of including the mass in the thermal envelope is interesting,
> but complicated, considering the complexity of grade beams and pier
> footings that were incorporated in the slab, not to mention its air
> barrier. the original grade was sloped as well, so the fill was a simple
> means of leveling the surface for the slab system.
>
>
>
> here's the significance of all this angst. this project was pre certified
> by PHIUS over two years ago. Now that the house is complete, and has been
> occupied for over a year, I'm finally getting around to documenting the
> as-built conditions, for final certification. When I revise PHPP to
> de-couple the slab from the earth, and use R-0.11 for the stone, and the
> value Norbert provided for specific heat, it bumps up the modeled heat
> demand for the entire house by 8-9%.
>
>
>
> On the face of it, it sounds dramatic, but then again the heat demand is
> so low to begin with, the net difference is miniscule. On the other hand,
> it bumps the house over the 4.75 KBtu PH maximum.
>
>
>
> If, however, I use the lesser R-value that PHPP prompts for dry sand:
> R-0.6 to R-1.0, the modeled heat demand plummets, even lower than my
> original projection.
>
> I had fiddled with these two values--soil heat capacity, and thermal
> transmission--during the initial submission to PHIUS, and was instructed to
> keep my hands off the default values that the spreadsheet is loaded with.
> If I honor those instructions, the house should pass certification, and
> this conversation (insofar as it relates to the project) is moot.
>
>
>
> But my preference is to reflect actual conditions. At some point, it
> begins to call into question the value of certification processes like
> this. The cost of the 9 inches of high density EPS foam was ponderous. I
> did a what-if analysis in PHPP of reducing the thickness to 2" of foam, and
> concluded that it would require only a few dozen extra therms a year,
> representing a payback period measured in many decades.
>
> factor in the chemical impact of the foam itself, and it's questionable
> whether this approach will go far to save the planet.
>
>
>
> -aa
>
>
>
> PS--thanks for noting the missing R
>
>
> Alan Abrams
>
> *certified professional building designer, AIBDcertified passive house
> consultant, PHIUS*
>
> *certified passive house builder, PHIUS*
> cell     202-437-8583
> alan at abramsdesignbuild.com
> HELICON WORKS *Architecture and Education*
> <http://www.heliconworks.com/index2.html>
>
>
>
>
>
> --
>
> === * ===
> Rob Tom T6015O
> Kanata, Ontario, Canada
>
> < A r c h i L o g i c at Y a h o o dot C a >
>
> (manually winnow the chaff from my edress if you hit "Reply")
>
>
> _______________________________________________
> Greenbuilding mailing list
> to Send a Message to the list, use the email address
> Greenbuilding at bioenergylists.org
>
> to UNSUBSCRIBE or Change your List Settings use the web page
>
> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org
>
>
>
> _______________________________________________
> Greenbuilding mailing list
> to Send a Message to the list, use the email address
> Greenbuilding at bioenergylists.org
>
> to UNSUBSCRIBE or Change your List Settings use the web page
>
> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/greenbuilding_lists.bioenergylists.org/attachments/20151208/c0bab415/attachment.html>