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Guidance for drying Doug Fir timbers in solar kiln

6/11/21       
Kelly Member

Rebuilding my garage/shop that was lost in the Santa Cruz fire last August. Doug Fir timber frame, with timbers ranging from 6x6 knee braces to 8x12 beams. Most elements are 7x7, 6x8, 6x10. Total BF is ~2,200, of which ~2,000 just started baking the past few days in a solar kiln we built a few weeks back from the VT plans. Kiln's net inside dimensions are ~22' long, 4' deep (front to back) and height ranges from ~4' to 8' in a ~37 degree slope matching our latitude. South facing, on a newly poured slab, sealed well and 2x4 + plywood walls insulated with R13 glass batts. Roof is dual pane polycarbonate sheets. 1" foam panels put on at night to help retain heat. Internals include on Honeywell residential 70 pint dehumidifier, one 1500W electric space heater, and four cheap box fans for internal recirc (two on each end). Exhaust fans on east and west ends of kiln, with gravity-driven vent flaps (closed when fans off, blown open when fans on). All electrical elements controlled by WiFi-enabled 110v outlets. Inside temp and humidity reported by WiFi-connected weather station indoor unit. Hygrometer going in tomorrow, as a check on RH reported by weather station unit.

I've read lots of the technical literature, studied the tables, schedules, recipes, etc., and would appreciate expert input on how many days or hours at various temp and RH settings. Goal is MC in the 9% to 11% range. Timbers milled within the past two months from DF logs dropped in late January, killed by the fire 4 months before being dropped. So to some sense they "air dried" before being dropped. Most are new growth, in the 24" to 50" diameter range. Several are old growth, with 200+ rings. My cheap $40 pin moisture meter says ~28% MC the moment my mill slices them open, and a couple months air dry stickered on the deck yields MC's ranging from 16% to 19%.

What other data can a provide to guide one of you black belts to recommend a "recipe" for achieving our KD timber frame goals?

Having a blast with this.

6/11/21       #2: Guidance for drying Doug Fir timber ...
Tennessee Tim  Member

Website: http://www.tsmfarms.com

Kelly, Gene may correct me BUT....
1) I think that MC goal may be incorrect for framing materials or from what I've read and heard. I think it's more a 18% range and that could of changed over the last few years. It would be too dry for most areas and regain to average MC of the area which equals more movement.
2) I've also read that the larger "kilned" timbers were bringing some MC down BUT more for the sterilizing (killing bugs) and sap setting part of "kiln dried" with the high temp. From my readings large timbers as 6"x6" and larger would required such a huge kiln time to appropriately dry that deep it isn't financially credible as thickness creates slower moisture removing time and gets slower every 1/4" you gain in thickness.
YES there are a few log claims for full kiln BUT....BUT..BUT my understanding is they start with standing dead AND still not positive dry to the core.
Happy cutting and building. Sorry for your losses BUT glad your still around to put back your dream.
I'm finishing up a timberframe install into a 20'x30' stud framed barn I wanted to salvage. IT'S been a challenge as everything was fitted into and not craned up. I actually lifted the whole barn to laser level using the bottom and main top beam plates and many come-a-long angle bracing as every inch lift required multiple adjustments.
What brand mill do you own??? I have a Cooks.

6/11/21       #4: Guidance for drying Doug Fir timber ...
Kelly Member

My mill is a Lucas 7-23 swing arm mill. I will also be milling and drying redwood (1" and 2" thick boards for decking, siding, etc.) and Valley Oak (a white oak) for trim, cabinetry, flooring, furniture, etc.

My system is entirely solar powered (other than the gas mill), so fans, dehumidifier(s), heater(s) all cost me $0. Forever. And I'm not in a terrible rush, though faster generally better, up to the point of wood damage.

I just put cheap $40 MC meter in the 8x8 posts in my Doug Fir timber frame in the home that survived the fire. It's been standing since 1994, and reads ~8.8% MC. All but a few of the large Doug Fir timbers I am milling will live inside, in same/similar climate as existing house.

6/11/21       #6: Guidance for drying Doug Fir timber ...
Tennessee Tim  Member

Website: http://www.tsmfarms.com

Those swing mills are amazing. I have the Cooks superwide 52" mill with 20' cut length.
I had a Hud-son Farmboss 36 with 24' cut bed prior. LONG timbers require special equipment to handle those lengths.

I can understand the house frame being 8.8% now, but I'd be curious when it was stood up the true mc was.. We also have to understand we're measuring skin MC and not core. The house would most likely be that to the core as 26 years to gradually balance out is a LONG time to dry!!!
Good luck with the project and keep us/me posted on the progress.
Thanks,
Tim


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