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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I used to use 6” foam (but as part of a foam on grade layout with no slab). It seemed to be that part of the curve where added resistance flattened out with additional thickness (actually about 4” with minimal benefit to 6” then negligible). Foam slabs at 6” are nice to handle (lay flat and effectively bridge an uneven gravel or sand base). Also seemed less potential for vibration over time causing shifts in the sub base. Since then have cut back to 4” with better specs for how the subbase is prepared. 4” can still span about 16” (if needed). <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>It is funny how materials get used excessively based on what we think they are doing as opposed to how they work – most footings can easily be 4” x 14” – most concrete walls could be reduced significantly with proper reinforcement design. I would happily eliminate concrete in a foundation entirely and float a building on foam – seismically much more responsive. Unfortunately eng working in geofoam applications are not too interested in simple residential.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Greenbuilding [mailto:greenbuilding-bounces@lists.bioenergylists.org] <b>On Behalf Of </b>John F Straube<br><b>Sent:</b> August-21-13 5:51 AM<br><b>To:</b> Green Building<br><b>Subject:</b> Re: [Greenbuilding] passive haus article<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Heat loss through the slab is the same as heat loss through an airtight wall. If someone told you that the physics are different they are not.<o:p></o:p></p><div><p class=MsoNormal>The difference is, the ground temperature is much more stable, and never as extreme as air or roof surface temperatures.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>I recoil at the notion of large amounts of insulation (even 4" of foam is a lot) under the slab because it does not save much energy, unless you use some weird energy model that does not relate to measured sub- slab conditions. The soil simply does not get that cold below slabs on grade or below basement slabs and it IS the temperature difference between the soil and the indoor air that drives heat flow.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>