<div dir="ltr"><div style="font-size:12.8px">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:</div><div style="font-size:12.8px"><br></div><div style="font-size:12.8px"> (oven dried) 0.11 and (not dried) 0.08 in units of h*ft^2*degF/Btu</div><div><br></div>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.<div><br></div><div>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. </div><div><br></div><div>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%.</div><div><br></div><div>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. </div><div><br></div><div>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. <br><br>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.</div><div><br></div><div>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. <br><br>factor in the chemical impact of the foam itself, and it's questionable whether this approach will go far to save the planet.</div><div><br></div><div>-aa</div><div class="gmail_extra"><br></div><div class="gmail_extra">PS--thanks for noting the missing R</div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature"><div dir="ltr"><font size="2"><font size="2"><span style="color:rgb(102,0,0)">Alan Abrams</span></font><b style="color:rgb(102,0,0)"><br></b><i><span style="color:rgb(102,102,102)">certified professional building designer, AIBD<br>certified passive house consultant, PHIUS</span></i></font><div><i><span style="color:rgb(102,102,102)">certified passive house builder, PHIUS</span></i><font size="2"><span style="color:rgb(102,0,0)"><font color="#666666"><i><br></i></font></span></font><font style="color:rgb(102,102,102)" size="1"><font size="2">cell </font></font><font style="color:rgb(102,102,102)" size="1"><font size="2">202-437-8583</font></font><font style="color:rgb(102,102,102)" size="1"><font size="2"><br>
<a style="color:rgb(102,102,102)" href="mailto:alan@abramsdesignbuild.com" target="_blank">alan@abramsdesignbuild.com</a><br style="color:rgb(102,102,102)"></font></font><a href="http://www.heliconworks.com/index2.html" target="_blank">HELICON WORKS <i>Architecture and Education</i></a></div></div></div></div>
<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><br><div><div>-- </div><div>=== * ===<br>Rob Tom T6015O<br>Kanata, Ontario, Canada<br><br>< A r c h i L o g i c at Y a h o o dot C a ><br><br>(manually winnow the chaff from my edress if you hit "Reply")</div></div></div><br>_______________________________________________<br>
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