Expert: Bruce E. Johnson - 2/17/2009

Question
hi, I AM WONDERING WHAT SIZE RAFTER IS NEEDED TO SPAN A DISTANCE OF 15' AND A 5/12 PITCH FOR A GARAGE ROOF.I WILL BE USING THE SPACE FOR A REC AREA AND COULD USE COLLARS BUT DON'T WANT THEM TO LOW. THE LIVE LOAD FOR EASTERN CANADA IS APPROXIMATLY 30lbs/FT. THANKS

Answer
Hi shane, when you say 15' span are you referring to from the center of the building to exterior or the entire room width?  If your entire room width is 30' and your rafter span is from the center to the outside is 15' then a minimum of 2x10 rafter with a 16" LVL ridge beam would be recommended.  If the entire room width is 15' and you are only spanning half of that then 2x6 can be used for rafters and a 2x12 ridge beam.  Collar ties are usually set at the top one third of the roof height.  In other words if the distance from the top of your bearing wall to the top of the peak is 9' then your collar tie would be set at 6' from the top of the wall. I want to stress however that I am not a structural engineer and any structural work should be approved by such to be on the safe side. I hope this information helps. feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com