Question
Does anybody know about the R-value per inch of dry sawdust or wood chips? I would like to use it in the attic of a kiln.
Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
Sawdust is not suggested, as it has a high fire risk, insect risk, rodent risk, compaction risk, decay risk and will lose insulation value when it gets wet (as a ceiling is virtually impossible to build with vapor leaks). The insulation value of fairly dry oak sawdust is about 0.5 Btu inch / hr / (ft x ft) / degree F. The value changes with MC and species, chip size, compaction, etc.
The R-value is about 1.4 per inch of thickness. A cubic foot of dry sawdust (R = 5) would weigh about 30 pounds, so the ceiling would have to be extra strong. Seems that a moisture vapor resistant insulation would be cheaper in the long run and would provide more insulation without the risks mentioned.
Now some things I have learned. When green lumber is added, the walls absorb a lot of the moisture when the kiln is coming up to temp. Then it lets it back out as the wood dries. This seems to keep case hardening down to almost nil. With woods like hickory and maple it also dries down quicker to prevent sticker stain. The Nyle unit has worked just fine and other than one blower motor, I have not had any problems. It runs all the time with just long enough time to load/unload. There has to be something to the thermo mass of the sawdust, as when we opened up the kiln it was 125 degrees in there. We removed1,500 bdft of walnut and put in almost 2,000 bdft of oak and it took about 2 1/2 hours to do this. Day time temp was around 74 degrees and when I closed it up and turned on the unit, the temp in the chamber was 92 degrees and within 4 hours was up to 125 (that was when I went by to check). The chamber is 12' w x 20' l x 10' h and sits on 6 inches of concrete that is sitting on 2 inches of foam. I need to get around and paint the outside someday.
