Join Date: Apr 2007
Posts: 4
04-11-07, 07:00 PM
#1
Determine roof rafter size
I need help in determing rafter size for a 6/12 roof spanning 24' distance. The vertical load on each wall is 600 pounds for each rafter/collar system. The rafter and collar form a treyed (trayed?) ceiling, with the collar (ceiling joist) being attached 2.5 feet above the top of the wall, thus, the top of the trey (ceiling joists) spans 14' at a height of 2.5 feet above the wall.
Help ....
jfxlee
Help ....
jfxlee
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Join Date: Apr 2007
Posts: 4
04-12-07, 03:28 PM
#3
Thanks snoonyb.
This is very helpful. I still have some concern that the tables are for a simple roof system where the ceiling joists are attatched at the top of the wall, where as, in the tray ceiling the joists are attatched 2.5 feet vertically above the wall.
Any additional thoughts on this ?
This is very helpful. I still have some concern that the tables are for a simple roof system where the ceiling joists are attatched at the top of the wall, where as, in the tray ceiling the joists are attatched 2.5 feet vertically above the wall.
Any additional thoughts on this ?
Join Date: Aug 2004
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Join Date: Apr 2007
Posts: 4
Join Date: Mar 2007
Posts: 230
04-13-07, 02:39 PM
#6
Collar ties are most effective when installed one third the run of the rafter down from the peak. Installing them lower (to form your tray) will not adequately transfer the load from the roof to the exterior bearing walls. Since your slope is a 6/12 your loading factor is mitigated somewhat but you don't specify the type of loading in your area. If you typically have extreme winters with significant snow loading, you may see additional deflection in the rafters. As the tray is forming the vertical load transfer, you may acquire some minor cracking in the finished ceiling. A better plan would be to beef up the rafters. The additonal expense is moderate compared to the potential for repeated repairs to the ceiling.
Join Date: Apr 2007
Posts: 4
04-15-07, 05:36 PM
#7
Thanks,
Although my primary concern is lateral movement, I had not considered the possibility of cracking the sheetrock. Considering this, I will beef up the rafters to the point of overkill with gussets, etc.. My loading requirement is approximately 40 pounds per square foot (Atlanta, max 8" snow).
Although my primary concern is lateral movement, I had not considered the possibility of cracking the sheetrock. Considering this, I will beef up the rafters to the point of overkill with gussets, etc.. My loading requirement is approximately 40 pounds per square foot (Atlanta, max 8" snow).