zc15
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- Thread starter zc15
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billconner
Well-known member
does seem to be rafters, not trusses. then they "hung" some ceiling joists and put in a strong back to support rest. You could raise these a third if the joists are not maxed out. Raised to a 1/3, rafters derate 20 or 30% iirc. posted that in another thread.
billconner
Well-known member
posted this from code:
Code has a simple table to adjust rafter span based on height of ceiling joist - your tie - to height of ridge, both measured from top of rafter support (wall plate). starts at 1/3 and adjust rafter span to 2/3, all the way to 1/7.5 is no adjustment. A 5' rafter span is nothing so should be fine. Connection is the only concern - nail sizes, number, pattern - easily accomplished.
Code has a simple table to adjust rafter span based on height of ceiling joist - your tie - to height of ridge, both measured from top of rafter support (wall plate). starts at 1/3 and adjust rafter span to 2/3, all the way to 1/7.5 is no adjustment. A 5' rafter span is nothing so should be fine. Connection is the only concern - nail sizes, number, pattern - easily accomplished.
billconner
Well-known member
moving one at a time with nomad load - ice and wind - I wouldn't bother buying one and leap frogging. You could probably remove every other one for a few days. Nailing is weak point - check schedules or overdo that connection.
billconner
Well-known member
I *think* I can, but not off the cuff. I'll look later today.
Any grade stamp on the rafters? I'm guessing long faded if ever there, so I'll assume SPF no. 3. Bug me if I don't get back to you in a day.
6:12 pitch?
Any grade stamp on the rafters? I'm guessing long faded if ever there, so I'll assume SPF no. 3. Bug me if I don't get back to you in a day.
6:12 pitch?
billconner
Well-known member
This is not an "expert" at work - just following through the prescriptive language of the IRC like a carpenter.
Working from IRC table for: Roof live load = 20 psf, ceiling not attached to rafters, L/Δ = 180), 10 psf dead load
Spruce-pine-fir #2 16" on center (????) 2x6 will span 14-4 (span is between inside edge of top pate and ridge - so maybe its really 11'-8"?)
If you raise the ceiling joist (what the code terms the "tie" at lower end of rafters) 1/3, the span is reduced 1/3 - so the 2 x 6 would only be good for 9'-7", not 11'-8"
The adjustment for raising it 1/5 - 14.4" - is .83 so 2x6 with ceiling joist raised 14.4 " will span 11' - 10 3/4" - so rounding off you could probably raise it 15" and still meet code - assuming all my assumptions on lumber grade and species, on center spacing, etc., are correct.
The allowable span of the same material as a ceiling joist is 16'-11", and raised 15" I think the span would be around 18' with no (storage) load - so a little undersized - just keep some hangers and the strong back, or change to 2x8s.
I don't think I'd raise them the 1/3 if it were my garage but probably wouldn't be afraid to let my kid into your garage in a snow storm if you did. Working with overhead loads and rigging, whether or not you'd allow your children under them is kind of the ultimate measure.
I'm happy to make run this again if my assumptions are off.
Was interesting - doug fir #2 would pass; hem fir and southern yellow pine are very close - like an inch or two off the 11'-8" mark with joists raised 24".
Working from IRC table for: Roof live load = 20 psf, ceiling not attached to rafters, L/Δ = 180), 10 psf dead load
Spruce-pine-fir #2 16" on center (????) 2x6 will span 14-4 (span is between inside edge of top pate and ridge - so maybe its really 11'-8"?)
If you raise the ceiling joist (what the code terms the "tie" at lower end of rafters) 1/3, the span is reduced 1/3 - so the 2 x 6 would only be good for 9'-7", not 11'-8"
The adjustment for raising it 1/5 - 14.4" - is .83 so 2x6 with ceiling joist raised 14.4 " will span 11' - 10 3/4" - so rounding off you could probably raise it 15" and still meet code - assuming all my assumptions on lumber grade and species, on center spacing, etc., are correct.
The allowable span of the same material as a ceiling joist is 16'-11", and raised 15" I think the span would be around 18' with no (storage) load - so a little undersized - just keep some hangers and the strong back, or change to 2x8s.
I don't think I'd raise them the 1/3 if it were my garage but probably wouldn't be afraid to let my kid into your garage in a snow storm if you did. Working with overhead loads and rigging, whether or not you'd allow your children under them is kind of the ultimate measure.
I'm happy to make run this again if my assumptions are off.
Was interesting - doug fir #2 would pass; hem fir and southern yellow pine are very close - like an inch or two off the 11'-8" mark with joists raised 24".