thermally modified wood

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Author Message Sheldon Wolfe Senior Member Username: sheldon_wolfe Post Number: 424 Registered: 01-2003 Posted on Monday, August 16, 2010 - 08:57 pm:    What experience have you had with thermally modified wood (TMW, TMT)? I found several sources on the web, looking for comments on how it performs. Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 875 Registered: 03-2003 Posted on Monday, August 16, 2010 - 09:03 pm:    Isn't that what you find after a building fire? :-) Ron Geren, AIA, CSI, CCS, CCCA, SCIP www.specsandcodes.com Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 298 Registered: 10-2007 Posted on Tuesday, August 17, 2010 - 12:06 am:    I would be concerned that the heat would have a negative impact on the strengh and stiffness. For most of the situations where it was proposed I doubt that there would be a problem but it could be a concern in some locations. Anne Whitacre, FCSI CCS Senior Member Username: awhitacre Post Number: 995 Registered: 07-2002 Posted on Tuesday, August 17, 2010 - 12:36 pm:    I have only minor experience with thermally changed wood -- and it ended up not being used on the project. The application of heat and steam breaks the cells in the wood, and that allows you to "rearrange" the wood fibers (in our case, bending it); but the structural results were inconsistent. I'm not certain if this is what you're talking about, and if its not, just ignore the whole post. Sheldon Wolfe Senior Member Username: sheldon_wolfe Post Number: 425 Registered: 01-2003 Posted on Tuesday, August 17, 2010 - 03:43 pm:    Good call, Mark & Anne; a couple of the sources I found indicated this type of wood should not be used in structural applications. For this project, it will be deck boards only, which seems to be its major use. The claim is that it is far more resistant to decay and bugs than anything except preservative-treated wood, and so does not require paint or stain; the price is similar to redwood. It's another one of those been-used-in-Europe-for-a-while products. What I've read looks promising, but if it's going to receive a field finish it may not make sense, as the finish still must be maintained. Ron, I'm sure that's what is meant by the "fire-treated wood" I often see noted on drawings. George A. Everding, AIA, CSI, CCS, CCCA Senior Member Username: geverding Post Number: 551 Registered: 11-2004 Posted on Tuesday, August 17, 2010 - 04:18 pm:    I'd never heard of it until this thread; I agree it seems interesting. I guess you can teach an old dog (or an olde wolfe) new tricks. And, I think Kiln Dried lumber could also fit into the "thermally-modified wood" classification. Let us know how it all works out, Sheldon. George A. Everding AIA CSI CCS CCCA Cannon Design - St. Louis, MO Sheldon Wolfe Senior Member Username: sheldon_wolfe Post Number: 426 Registered: 01-2003 Posted on Tuesday, August 17, 2010 - 05:52 pm:    I have the typing trick down; I've just about learned "sit" and "speak". This process is longer, and at a much higher temperature than kiln drying. Normal kilns are about 165 degrees F; this stuff starts at 210 degrees for drying, then goes to 450-plus degrees. At that temperature, the structure of the wood changes, which makes it more resistant to decay. One process takes 50 to 60 hours. In personal experience, I find kiln drying to be something of a myth; one supposedly KDAT (kiln dried after treatment) 2x6 will weigh five times as much as another, and sometimes, when driving screws or nails home, the water literally squirts out. J. Peter Jordan Senior Member Username: jpjordan Post Number: 441 Registered: 05-2004 Posted on Wednesday, August 18, 2010 - 10:21 am:    I have had a rep call on me. The process originated in Europe, but there is now a company in the States doing it (southern IL if I remember correctly). Originally conceived for deck planking (which I would argue is structural), the "baking" process removes much of the non-cellulose material in the wood leaving it much more resistant to rot and insect attack. The company primarily uses No. 1 grade so there are very few knots or other defects, and the process results in a dark honey colored wood. The dimension shrink somewhat, and it does weaken the wood. I have asked if we could get it in No. 2 or No. 3 grade for use in blocking associated with roofing, but I think even with the premium cost of the processed product in a No. 1 grade, it might be cost effective when compared with preservative treated wood when you have to include the cost of isolating the treated wood from steel and the requirement to use stainless steel fasteners. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1232 Registered: 03-2002 Posted on Wednesday, August 18, 2010 - 10:24 am:    Interesting thought on roof blocking. We currently specify 'moderately decay resistant' species for roof blocking, as defined by the National Forest Service: Douglas fir or Larch. This avoids the cost of dealing with PT as you note. In all the years I did roof evaluations and replacement, rotten wood blocking was rare. Richard L. Hird (Unregistered Guest) Unregistered guest Posted on Wednesday, August 18, 2010 - 03:03 pm:    I would not be worried about using it as decking if the manufacturer can provide some allowable design stresses, (even if reduced from standard decking it is probably adequate). Stress grading it for support framing requires a greater leap of faith. Curt Norton, CSI, CCS Senior Member Username: curtn Post Number: 169 Registered: 06-2002 Posted on Wednesday, August 18, 2010 - 09:26 pm:    Treated lumber shouldn't be used in roofing. It is wet as Sheldon points out, adding moisture under the membrane, it is more expensive and reacts with the fastners. If you have rotting wood under your roof membrane, you have bigger problems than rotten wood. If the blocking sits on poured concrete, I could be talked into one layer of treated, but even then I think it's a waste. off topic a bit, but...