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Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Roughsawn Hemlock for Framing Lumber 
Question
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. Forum Responses
From contributor D: The knowledge base here has several good threads relating to this. Here is one below. > Grading Lumber For An Addition 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. > Certified Construction Lumber
From contributor P: What is the overall size of your cottage? I’m thinking that your wall studs are fine (2X6's are overkill anyway for wall studs, and are used so you can fit R-19 fiberglass into the cavities). Your 2 X 10's should be fine if your span is no more than 14'. More than 14' and I would go with 2X12's. Blocking will also help 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.
From the original questioner: To contributor P: The overall dimensions of the cottage will be 24' wide x 30' one story and built on a crawl space foundation. From contributor D: I was at the CWC website recently, and below is a link to their span calculator. Eastern hemlock falls under "Northern Species" in their table. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
From contributor P: Again, I think you lumber sizing is fine for a 24' wide house, although I have never framed with Hemlock. You might want to ask for specifics about the peculiarities of framing with hemlock. 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:
Your design sounds similar. Again, you could bump up the rafters to 2X8's to gain insulation space.
From the original questioner: To contributor P: What wood species did you frame with in northern NH? Also, did you make your own design or blueprint? I have changed my wood species for the floor joists to beech 1.5" x 9.5" clear grade lumber. I thought that the beech lumber would be much stronger, and especially if I spaced the floor joists 16" O.C. I'm now comparing beech and yellow poplar for the wall studs and roof rafters. I have estimated it would take approximately 6,000 board feet of lumber to frame the home. From Gene Wengert, forum technical advisor: I disagree with the posting by Contributor P stating that 14' span is ok. In truth, it depends on the grade of the lumber. Further, the presence of large knots is not an indication of strength. Slope of Grain (SOG) and compression wood are very large strength reducing characteristics. Also, knots that are close to the edge and spike knots reduce the strength greatly even if fairly small. 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.
From the original questioner: It may be a good idea to hire a certified structural engineer, for the stamping of the lumber and for the engineering of the wood framed structure. I don't know what the costs would be to hire an engineer for a cottage style home. The costs associated with hiring an engineer may or may not be feasible for a project of that size. Computer Aided Design software could also be a good option for the builder to use on a project like that. The software could help in the engineering, organizing, and planning for the construction of the home.
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