Expert: Dan Griffin - 1/22/2009

Question
Recently, I decided to enlarge my freestanding garage.  It will be approximately 26' x 24' with a small 45 degree jog on one corner.  I am a novice and think I may have bit off more than I can chew -- OOPS.  Money prevents me from hiring a professional to do this job.  I plan to put a cabled roof and would like to have a vaulted ceiling.  Could you offer any input to this project?  I will be using standard 2X4 framing for walls and 2X6 or 2x10s for rafters.  The height of the roof will be 4 or 5 feet -- so basically a length of 13' (half the 26' total) by 4' high.  Also I was thinking of using the metal brackets to attach the rafters to the beam.  Finally, I live in Houston, Texas so my only worries are rain and an occasional hurricane.

Answer
Tom, the vaulted ceiling is out unless you make a major engineering change or go to trusses.  You need the ceiling joists to tie the bottoms of the rafters together or the side walls will push out and the roof will collapse.  It can be done with a structural ridge, but it would be substantial to span 26 feet.  I don't know the code requirements for wind/snow/seismic in your area.  The rafter span of 13 feet using a 20 pound live load and 10 pound dead load will require 2x8s even on 16" centers.  If you can reduce the live load to 10 pounds, the 2x6 will suffice, but this is a code issue.  YOur local code official should be willing to share local load requirements.  A builders' desk at a real lumber yard may also be able to assist sizing requirements for your area.  JOist hangers are not very normal for rafters at the ridge.  Wind codes will probably require strapping or Simpson ties at the top plate.

I think you should at least call and price trusses as they will simplify many issues.