pumice for insulation?
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David Burdick
Feb 20, 2013, 5:49:23 PM2/20/13
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Have any of you used/specified pumice
for insulation under concrete/earthen slab floors?
As you know, insulation isn't required under slabs that don't contain hydronic or other heating systems; apparently passive solar slabs are not considered to be heated, insulation not required. Only R-10 is required under heated slabs; that--or none--may be enough under solar slabs in very sunny climates, but here on the cloudy side we don't get enough winter sun to heat the slab and the ground under it, which is a 20˚ ∆T heat sink 24-7-365. I believe that only requiring R10 is a concession to the high cost of XPS, and that much more would be much better. But XPS is expensive, not recyclable, blown with ozone-destroying CFCs, and never degrades; 1000 years from now, much of it that we put under houses today will still be swirling around one of the oceans' six great garbage gyres, choking sea turtles and fish to death and poisoning--everything.
Pumice involves no greenhouse gasses, no process energy, and only enough fossil hydrocarbons to dig it out of the ground, crush it just enough to make it consolidate well under a flat plate compactor, and haul it over here from Chemult. A 65 cu yd semi-trailer full would cover 1170 sf 18 in. deep; even if it's only
R1.5/inch, that's still R27, almost three times the minimum required. 65 yds of "oversize," at $9 a yd, would be $585; sending it over here on a truck is ~ $850, or ~ $1450 total (South Central Pumice LLC). By the unit, 2" XPS is ~$50/4x8 ft sheet 2" thick (Parr LBR); 1170/32 is 37 sheets, or $1850. Less money, 3 x the performance, and virtually no environmental problems. What's not to like?
I'm convinced this will work, as long as I keep the pumice above any water table. It's not hygroscopic, but will absorb water through capillarity--I wonder if I need a capillary break under it? M/VB goes between pumice and slab; warming the slab should drive any water out of the pumice, into the ground. Keep the ground below it dry--and even over here in the wet, the ground under a properly designed and built crawlspace is always bone dry--and I don't see any problems. But I need to convince the local code officials.
Anyone have a laboratory-proven (acceptable to a building official) R-value for Central Oregon white pumice? Anybody actually done this? If I can cite your success as a precedent.... Anybody used a different layering than earth, pumice, M/VB, slab? Think I need a capillary break--a few inches of drain (or even compacted crushed) rock under the pumice? Your thoughts and comments will be appreciated!
John O'Renick
As you know, insulation isn't required under slabs that don't contain hydronic or other heating systems; apparently passive solar slabs are not considered to be heated, insulation not required. Only R-10 is required under heated slabs; that--or none--may be enough under solar slabs in very sunny climates, but here on the cloudy side we don't get enough winter sun to heat the slab and the ground under it, which is a 20˚ ∆T heat sink 24-7-365. I believe that only requiring R10 is a concession to the high cost of XPS, and that much more would be much better. But XPS is expensive, not recyclable, blown with ozone-destroying CFCs, and never degrades; 1000 years from now, much of it that we put under houses today will still be swirling around one of the oceans' six great garbage gyres, choking sea turtles and fish to death and poisoning--everything.
Pumice involves no greenhouse gasses, no process energy, and only enough fossil hydrocarbons to dig it out of the ground, crush it just enough to make it consolidate well under a flat plate compactor, and haul it over here from Chemult. A 65 cu yd semi-trailer full would cover 1170 sf 18 in. deep; even if it's only
R1.5/inch, that's still R27, almost three times the minimum required. 65 yds of "oversize," at $9 a yd, would be $585; sending it over here on a truck is ~ $850, or ~ $1450 total (South Central Pumice LLC). By the unit, 2" XPS is ~$50/4x8 ft sheet 2" thick (Parr LBR); 1170/32 is 37 sheets, or $1850. Less money, 3 x the performance, and virtually no environmental problems. What's not to like?
I'm convinced this will work, as long as I keep the pumice above any water table. It's not hygroscopic, but will absorb water through capillarity--I wonder if I need a capillary break under it? M/VB goes between pumice and slab; warming the slab should drive any water out of the pumice, into the ground. Keep the ground below it dry--and even over here in the wet, the ground under a properly designed and built crawlspace is always bone dry--and I don't see any problems. But I need to convince the local code officials.
Anyone have a laboratory-proven (acceptable to a building official) R-value for Central Oregon white pumice? Anybody actually done this? If I can cite your success as a precedent.... Anybody used a different layering than earth, pumice, M/VB, slab? Think I need a capillary break--a few inches of drain (or even compacted crushed) rock under the pumice? Your thoughts and comments will be appreciated!
John O'Renick
Bronwyn Barry
Feb 20, 2013, 7:55:58 PM2/20/13
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I know many in the PH community refuse to visit this website, but Armando Cabo shared some helpful info and links on the GreenBuildingAdvisor website here:
Good luck!
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Glenn Haupt
Feb 21, 2013, 12:38:31 AM2/21/13
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Hi David,
Oregon Code will require min of r10, 24 inches horizontal perimeter insulation under your unheated slab, or a frost skirt insulation design depending on project location. The insulation must be be thermally broken @ the mudsill, so the detailing is tricky depending on your wall thickness and your bearing wall location. If u are going for passive house then use phpp to determine how much r value u need under the slab. U may look to dynamic r values offered by pumicrete for modeling purposes, and provide this to your building official. I have access to this data, give me a call 541-610-7351, Friday of this week or next.
If u don't have good solar contribution , or the ratio of south window area to heated floor area isn't good, u may want to scrap the slab and go for a warm floor instead. Pour a rat slab and then use a sleeper floor framing over it, blow in dense packed insulation and your choice of flooring. Concrete is not for everyone, durable for sure but pretty hard on the body. Have great fun with your project, much better to see this post question then has been going on recently! ;) cheers to all!
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Sent from my iPhone
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Adam Cohen
Feb 21, 2013, 8:03:39 AM2/21/13
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In the EU it is not uncommon to find folks using Foamglass for fill. If you can get pumice that cheap and keep it dry, do a project and insert both moisture and temp monitors under the slab to verify the hypothesis. Proabbly 300 work of instrumentation and a year od data would tell alot.
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Adam Cohen
Certified Passivhaus Consultant - North America and Europe
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Adam Cohen
Certified Passivhaus Consultant - North America and Europe
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Design/Builder of the First US Passivhaus Public School Building
2012 VSBN Green Designer of the Year
Structures Design/Build, LLC
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Structures Design/Build, LLC
5104 Bernard Drive
Roanoke, VA 24018
Web site: www.structuresdb.com
Passivhaus information: http://www.passivehousedesign.us/
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