Green or Kiln Dried Heavy Timbers?
Green or Kiln Dried Heavy Timbers?
(OP)
I have a project this is a heavy timber framed picnic shelter. It will be comprised of heavy timber trusses supported by heavy timber columns. The lateral stability is provided by diagonal bracing.
I am trying to decide if I need to call for these timbers to be kiln dried or green. The column members are fairly large (8x8) and some of the truss members are also fairly large (8x8's or 10x6's) to accommodate the architect's desired appearance.
As I understand it, in air drying pieces of this size, it takes about a year to bring 1" of the material down to 19% or so moisture content. As I understand it, kiln drying does it faster, but the inside may be still wet while the outside is relatively dry.
I know that historically, these structures are built with green materials....not kiln dried and not air dried. Cut, brought to the site, and then erected.
Has anyone on this board worked with these materials and has a preference one way or the other?
By the way, I am requiring the columns and diagonal brace materials be pressure treated, as they will likely be exposed to rain. Thank you for your consideration.
I am trying to decide if I need to call for these timbers to be kiln dried or green. The column members are fairly large (8x8) and some of the truss members are also fairly large (8x8's or 10x6's) to accommodate the architect's desired appearance.
As I understand it, in air drying pieces of this size, it takes about a year to bring 1" of the material down to 19% or so moisture content. As I understand it, kiln drying does it faster, but the inside may be still wet while the outside is relatively dry.
I know that historically, these structures are built with green materials....not kiln dried and not air dried. Cut, brought to the site, and then erected.
Has anyone on this board worked with these materials and has a preference one way or the other?
By the way, I am requiring the columns and diagonal brace materials be pressure treated, as they will likely be exposed to rain. Thank you for your consideration.






RE: Green or Kiln Dried Heavy Timbers?
RE: Green or Kiln Dried Heavy Timbers?
Any suggestion that they use kiln dried material to fabricate their heavy timber framing was met with flat rejection. We have not detected any significant problems with the process of using green timbers.
RE: Green or Kiln Dried Heavy Timbers?
Literature suggests shrinkage when drying is greatest in the crosswise direction, which I guess explains why the joist are less tall now.
http://www.awc.org/helpoutreach/faq/faqFiles/Shrin...
http://www.motherearthnews.com/green-homes/green-w...
Also that initial deflection and "creep" of wet/green lumber is much greater than for seasoned lumber.
file:///C:/Users/Robyn%20Timberlake/Downloads/TB-101.pdf
RE: Green or Kiln Dried Heavy Timbers?
I like designing heavy trusses with glulam. Architect had some on a church sand-blasted and it gave a great look. The glulam of course can be rendered dry relatively easily. The glulam can even be made out of decay resistant lumber if that interests you.
RE: Green or Kiln Dried Heavy Timbers?
If you are using pressure treated, they will be wetter than original lumber unless air dried for quite awhile.