I have some eastern hemlock timber that I would like to saw for structural lumber, for a one story cottage style home. The framing lumber will be 1.5" thick x 5.5" wide x 92 5/8" long for the wall studs spaced 16" O.C. The floor framing lumber will be 1.5" thick x 9.5" wide x 14' long spaced 16" O.C. with two 6" thick x 10" wide x 15' long solid timbers. The roof lumber will be 1.5" thick x 5.5" wide x 16' long for the rafters, and two 1.5" thick x 5.5" wide x 12's long overlapped with two 1.5" thick x 5.5" wide x 6's long.
Would I need to get a structural engineer to analyze my home plan and wood species and timbers used in the framing of the home? Any advice on structural lumber, wood species and the grading and engineering of will be appreciated.
(Sawing and Drying Forum)
From contributor M:
I would suggest that you check with your local building inspector as the rules vary from state to state.
Also, in the link below, Dr. Gene Wengert points out something we all need to keep clearly in mind whenever the inspector does let us use our own lumber. "When the first roof falls in and it was made of uncertified lumber, things will get under even more government control. All it takes is one bad apple..."
Beat the grade clearly and do the engineering properly, otherwise we all lose. I went down to TPI last month and took their 4 day dimensional lumber grading class, and I got a lot out of it. Graders from any of those agencies can also grade your lumber for a fee. You can probably find your span info on CWC's website, the Spancalc I think it will list your hemlock.
The same goes with the rafters. 2x6x16's 16" O.C. should be fine too. In heavy snow areas, a knee wall or collar beams will help a little on the loading. I would keep the horizontal span to less than 12-13', or use knee walls and collar beams.
Some people like 2X8 rafters though to allow 6-1/4" fiberglass insulation and a cold air space to allow venting from the soffits to the ridge (to prevent ice dams). Just look over the lumber and don't use ones with big knots and obvious defects.
For a typical 24 X 32' cape house in Northern NH, I've used Carrying Beam 3- 2X10's laminated together with two posts evenly spaced.
First floor joists:
2X10's (dressed .i.e 1.5" X 9.25")
Second Floor Joists
Your design sounds similar. Again, you could bump up the rafters to 2X8's to gain insulation space.
In addition to strength, the amount of wane is a factor, as you need to be able to nail to the edge. Straightness is also an important factor. Hemlock presents special issues due to the presence of wetwood (very weak) and shake, in addition to copious amounts of compression wood. Finally, check with the building code people as what looks good to you may not pass if it is not stamped with a grade.