Expert: Dan Griffin - 5/21/2008

Question
hell...Iam building a lean to off my barn. Its going to span out 16 feet. Iam
wondereing what size lumber to use as trusses. it will be a tin roof and we have
a low snow load. I am using 6x6 posts on 10 feet centres.Also what joist
spacing? thanks

Answer
Sean,  if you are using trusses, let the truss company work out the engineering.  They will probably use 2x4 unless you intend to pull motors or hang some other substantial loads from the bottom chord.

You probably don't really mean to use the word truss.  For proper cut roof material requirements you will need to know the snow load, dead load, live load allowance, and wind load for your area and application.    A lean to needs a much higher snow load because the snow from the upper level can slide there and/or drift there.

For information on spans here is a good site:
http://www.awc.org/calculators/span/reversecalc/reversecalc.asp
You can adjust type of lumber, deflection, and loads.  It would be inappropriate for me to size our loads without more information.