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Kiln Drying timbers

Started by Old Wood Whacker, May 15, 2020, 03:08:43 PM

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Old Wood Whacker

I am planning on building a 32x 38 single story addition to our home in timber frame and I am wondering if it is possible and/or practical to kiln dry the posts and beams. It make have been discussed here , but I can't seem to find it. If so, what are the advantage and disadvantages? I will be sawing the timbers myself, and I do have kiln access, although, if it is something that is possible, then I'm sure I will need some kiln schedule info regarding how to approach drying them. Any help would be greatly appreciated.

Don P

What species are you using? Basically the closer wood is to in-service moisture content the fewer surprises later as the wood shrinks. I don't know of published kiln schedules that go thicker than 16/4 but quite a few log home companies kd up to 8" thick pine. I would air dry for quite a while to lower the gradient when you do stick it in the kiln or you will have a very long mild period in the kiln that probably won't be cost effective. Calling @K-Guy :)

Brad_bb

Timber frames are normally built with Greenwood because it's not practical to try and dry large Timbers. It just doesn't work with hardwood Timbers. Sometimes they vacuum kiln dried clear coastal Doug for Timbers, but those are the only ones I know of that anyone attempts to dry. Everything else is built green. I have milled a lot of my own Timbers and I mail them slightly over size and they end up sitting in my shed for 1 to 4 years before I will use them. Before I go to use them I can plane that oversize off to make sure the timbers are square before doing any layout. I think letting the rough sawn timber sit for a year or more helps to stabilize them.  White oak timbers can take longer than that to stabilize, and sometimes they'll have a mind of their own and in two years will bow or crook in a certain way. Not all of them but once in a while. The best circumstance is to either Cut the frame right away and assemble it right away before anything can move, or do like I do and let the timber sit and then re-square them just before you go to use them. Drying slow it's a good thing for them. If you try to dry a hardwood timber in a kiln, I think you're going to see some severe checking problems and movement, because you're drying it too fast and you're just drying the shell.
Anything someone can design, I can sure figure out how to fix!
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K-Guy



Air drying is the best way to start drying posts or beams, since it is slower, it is gentler and you get less cracking ad splitting. Notice I said less, you cannot avoid some, also some species will have more than others. Generally softwood will have less and dry quicker than hardwood. This is due to internal stress in the wood caused by the uneven shrinkage from the outer rings compared to the inner. I'm sure Gene Wengert could give a better description than I can. Many of the companies that KD beams only put them in at the end to get a lower final moisture and sterilize.
Nyle Service Dept.
A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.
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tule peak timber

I agree with all above...
  Another option is to pick a species that you have experience with, that tends to dry more or less dimensional stable and build  with green timbers .This is an option I picked for a 20 X 36 I'm working on now.
persistence personified - never let up , never let down

Don P

Thanks Stan, judging by the size of the air drying stacks of white pine timbers at the log company up the road from me I'd say that is likely the way they operate. White pine is one that doesn't move a great deal as it dries, but it also dries fairly rapidly. I'm sawing a stack of EWP timbers now that will probably sit on stickers for a year before framing. It might go into the kiln but I'm not too concerned at that point if it doesn't. Oak would be a different matter, going back to what Tule Peak is saying.

A timber that has been drying for 1-4 years is not green. In the trade they are referred to as PAD or TAD. S-GRN is the nomenclature for surfaced green. S-Dry is typically assumed for surfaced at 19% or below. PAD stands for partially air dried, pretty common in large timbers running on through totally air dried when the core has balanced. This is a good descriptive page from Eric Morley's site;
https://www.carolinatimberworks.com/best-wood-timber-framing/


tule peak timber

A shout out to Don P for his help in my decision making process. Thank you.
persistence personified - never let up , never let down

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