Dry material, green timber interface

Hello everyone and thanks in advance for sharing.

My clients contractor is trying to understand what will be going on and how to deal with the interface between kiln dried materials and green timbers, especially at the eaves.

The project is just now in conception so no plans have been drawn, but the house will probably be a story and a half with continuous top plates and common rafters. Oak will be the pedominating species in the frame.

I have a basic understanding of how wood shrinks and experience working with oak, but my experience with enclosure systems is limited. I hope to be able to tell the contractor something other than "they do it all the time." We are not sure yet what kind of enclosure will be used. It may be SIP's or site built 2x panels. I imagine that if the panels were screwed to the neutral axis of the plate than the oak can shrink without effecting the dry material very much. And maybe there would be some gaps built in between the panels to be filled with foam?

Any advice is greatly appreciated.

Kevan

Well, I may have been a bit vague as to what I am trying to find out.

I am trying to understand what may or will happen over time to an encolsure system (be it site built 2X panels consisting of kiln dried lumber, or SIPs) when the green timber the enclosure is attached to shrinks down to it's dry timber size.

The main concern is where the wall panels meet the roof panels at the eave. In a house where common rafters rest upon a continuous top plate, might there be a problem due to the plate and the rafters shrinking in cross section? Might the panels collide (for lack of a better term) at the eave and cause problems? Is there a method people are using or panel companies are recommending to avoid/deal with these potential concerns?

I know that enclosure panels are attached to green frames all the time, but my clients contractor is not too familier with timber framing in general let alone enclosure systems. He is wondering why not just get kiln dried timbers.

Thanks again,

Kevan

Kevan -

PM sent.

-Mike

Kevan:
Years ago, at a pre-conference workshop, we were told about such things happening:



So to prevent this from happening you have to figure the amount of total shrinkage expected and leave a gap between the wall sip and the roof sip of this much. And while waiting for the settling fill this gap with foam, foam from the spray can type foam, it will compress as the building settles.

Others may have more advice.

Good luck...
Jim Rogers

I would be curious to see the engineering numbers on the compression of the sprayed in foam. Will it really compress? You can put a whole building on foam, under a slab.

I think I recall reading about this similar topic, somewhere too, whether it was a full bent raising with no top plate or a building with a top plate. Each side had positive points and it came to a stand still. Basically it was a personal choice as to what type of structure you wanted to deal with.

Use a natural building material, like clay, that shrinks more than the timber and don't worry about it.

Tim

Thanks Jim and TIm. That is along the lines of what I thought might be the best way to deal with these concerns.

Kevan

Hi Kevan;

I work with old buildings and I cannot say I have ever noticed a problem due to shrinkage in a timber frame. Horizontal log buildings are certainly a different building category and shrink substantially.

Old (and new) buildings have a much greater occurance of problems from a timber twisting as it drys. Watch out for that left hand spiral grain.

Jim