Expert: Bruce E. Johnson - 9/14/2009

Question
QUESTION: OK my question is ...I am about to build a small house and the plan we picked was of a lofted house. now I want to make the entire area living space. if I am using 2by8 floor joists what is the max I can go without needing support?

ANSWER: Hi bryan, I wouldn't go over ten feet of span with a 2x8 and that would be spaced at 16".  I hope this information helps please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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QUESTION: HI and thank you for your answer it is very helpful. one more for you...when I do my rafters and my span is 24'.. I am doing a 12/12 pitch by the way how long and what size should they be...my guess is no less then 2by8 at about 18'5" is this good?


Answer
Hi again bryan, when you say 24 foot span I am assuming that you mean the building is 24' wide and your span from ridgeline of roof to outside wall is 12'?  A 12/12 pitch on a 12' rafter span gives you 12 feet of height at the peak.  To determine rafter length you add the squares of the two right angle sides, in your case the square of 12 is 144 both directions..so 144+144= 288..then you take that number 288 and get the square root of that which = 16.97' or almost 17 feet.  For a pitch this steep, a 2x8 will work okay but I recommend a row of solid bridging at mid span of each rafter side. As in any structural design I always recommend you consult with an engineer for your final construction plans. I hope this information helps please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com