[Strawbale] Strawbale Digest, Vol 11, Issue 7

[Derek Roff]

> A guy was asking me offlist about [bug problems] using oak for beams
> cut onsite in houses.

There are many species of oak in North America, but only a few appear 
in the commercial market.  Before using site-cut oak, it would be 
useful to try and find out whether the on-site species has 
characteristics similar to the commercial varieties, for which we have 
extensive building/testing experience.

The odds are that any on-site oak large enough to cut the beams from 
will have acceptable characteristics.  All woods can be eaten by a 
variety of bugs.  Most oaks will resist insects somewhat better than 
the average for North American structural woods.

RT has already mentioned that most of the problems with site-cut wood 
derive from lack of proper drying, rather than from species.  I'd like 
to amplify some of his comments and debate one of them.  Green wood has 
much less strength than the same wood will when properly dried, and it 
weighs a great deal more.  For these reasons, green timbers may fail 
during construction, even if the span tables indicate that a house with 
timbers of that size would be "overbuilt".

As RT mentioned, green wood may distort dramatically and unpredictably 
as it dries.  Most fasteners and woodworking joints will loosen 
substantially as the wood moves from green to dry.  Any cross-grain 
connection (which is almost all of them, in a house) will be highly 
stressed and may crack.  I would debate whether it is possible to 
reliably resist these distortions after the timbers are incorporated 
into a structure.  If you are lucky, the growing conditions and species 
of the site-cut wood will not present severe problems.  But problems 
are likely.

Drying the wood prior to use is a good idea.  Air drying is possible, 
with the wood properly stacked and covered.  Site-built solar kilns are 
a practical method in many locations.  In every case, time will be a 
factor.  Rushing the use of the wood is risky.

Derelict

Derek Roff
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek at unm.edu