Should I use 2x8 or 2x10 for rafters with a 30 foot length? I do not want my roof to collapse or have any really bad weak spots in it.

Answer by  thelostone (1457)

There are other factors in choosing sizes of rafters besides just the length. The biggest factor is the longest span that will not have support below it.

Answer by  eyeguy (3760)

2 x 10 rafters are the best choice in your application. If properly constructed the weight should not be an issue. Proper construction has physics and geometry working on its side. The larger rafter will give you outstanding support for years to come. Weak spots are normally an issue of the sheathing not the rafters.

Answer by  Anonymous

Thirty feet is an extremely long unsupported span. You must speak with an engineer to ensure your roof is safe. There is no option ( not even 2x12 DFir) in regular lumber for such a span. Google the AWC span calculator.

Answer by  cheygavara1 (33)

Everything depends on the pitch of the roof. If it is a strong pitch (angle) then a 2x12 at thirty feet might work. Are there going to be snow loads? Is anything going on this roof beyond its covering (shingle, rubber? ) I would not use 2x8.