open beam for cathedral ceiling

[Jim_Rogers]

when you calculate your roof truss dimensions otherwise your roofline will not be straight.

It has been seen in past constructions that due to the shrinkage factor of a timber frame that the roofline, mentioned above, will never stay straight. Most designers and or builders will not attempt to make them the same. The offset them intentionally to maintain a seam that will be weatherproof.

Jim Rogers

[nanook]

Is this the case even if the wood in the framing has been dried?

[Jim_Rogers]

Is this the case even if the wood in the framing has been dried?

Rarely is the wood of a timber frame house been dried. Most are made from green timbers.
Drying a timber for a timber frame is very expensive and not normally done.

[nanook]

I hope to get and mill the rafters, king beam, floor joists, studs, etc. this winter and set them to dry in our drying shed. In the past when we have done this our 2"x4"'s, 2"x6"'s etc. have dried quite well. I guess you are saying that it is common practice in this type of construction to use green wood for the timber frames.

[Jim_Rogers]

nanook;
There is quite a difference in drying a 2x4 in a drying shed then drying a large timber. Most air drying of softwoods timbers could take years to dry to the point where shrinkage won't be a factor.

[scrout]

Hi Nanook,

I am hoping to make something similar to this, in a 20x30 for a beach cabin.
But my beams would only be 20 foot span, pretty doable.

These guys do awesome work:
http://www.davisframe.com/timber-frame-post-beam-pictures-photos/Custom-Design-Galleries/Japanese-Tea-House-Timber-Frame-Gallery.aspx

[Thehardway]

Jim raises a very good point that I did not consider and should have. I was thinking merely in terms of your deck thickness and truss dimensions without taking into account the fact that one side will shrink and the other should not.  I agree with him 100%.  Put a slight intentional break in the roof line if you decide to take the hybrid approach and you resolve the potential for future problems. There are rules of thumb for shrinkage based on the overall dimension of the wood but these are only estimated and vary from timber to timber and by specie.

As for drying your timbers, it is nearly impossible to get anything the size you will need to air dry and is probably worse to try and kiln them as all you will do is case harden them and make your joinery work more difficult. Some of the big commercial shops have radio kilns (think giant microwaves) to dry timbers but it is very expensive as previously mentioned  and not necessary when do hand joinery. I think it is good to "season" them before doing joinery.  This process is basically cutting them to a nominal dimension for use in your cut list, then cribbing them to air dry in a shaded and well ventilated location, even covered with tin outside for several months before you do the joinery work.   This lets them move and show any negative tendencies they may have. You will probably have some which try to twist or bow during this period and you can cull these out or use them for smaller pieces.   

[nanook]

I really am thankful for all the responses and the great advice and suggestions. If I get this project off the ground I am sure I will have many more questions.     Nanook