Equilibrium Moisture Content and Geographic Location

      Here's info on how to estimate the expected moisture content of wood in the outdoor environment in different regions of the country. July 18, 2013

Question
I'm located in the GA piedmont, and have been commissioned to build an outdoor (covered) table. What MC range should such a piece be designed for? My hunch is 12% to 20%, but I really have no scientific basis for this.

Consider a frame and panel that is subject to natural humidity and temp changes, as well as occasional blown rain. What would be your process for determining the range of movement? Rules of thumb are fine. We all know that wood moves. We can easily find out how much each species will move with specific changes in MC. I'm looking for the missing link; is there an easy way to estimate the range of MC that a piece will likely encounter?

Forum Responses
(Furniture Making Forum)
From Contributor D:
I believe Hoadley's book "Understanding Wood" has EMC charts for North America. The FPL site should also have EMC charts. The question is, do the charts apply to exterior work, or indoor? My experience in the Midwest tells me that 11% is our exterior EMC.



From contributor K:
Contributor D's sources are good. To get a direct reading, test a piece, ideally of the same species as you plan to use, in your area in similar conditions with your moisture meter. That will at least tell you what the local EMC is at this season. In Vermont it would range from 11-14% outside under cover.


From the original questioner:
Thank you both. Contributor D is right - figure 13-1 in the "Wood Handbook" on the FPL site for others interested.


From Professor Gene Wengert, forum technical advisor:
Check page 5 of this publication. Note that the link below has EMC values for many locations in the USA.
Equilibrium Moisture Content of Wood in Outdoor Locations in the United States and Worldwide

Note that Burlington, VT ranges from 11.7% to 14.2% EMC.



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