I have an old, 1930s garage. I'm going to be tearing off the roof, rafters, etc. It's about 18' wide x 15' 6" deep. That means I can run 16' boards for the ceiling joists. It's in CA, no snow and I don't need storage in the attic, so I'm not too concerned with load. It's going to be about a 6/12 pitch. Recommendations on ceiling joist and rafter sizes and spacing?
New rafters for small garage
- Thread starter Don_Juan
- Start date
mike93lx
ALLIANCE MEMBER
There are lots of span and sizing tables online. Is this being inspected?
Without looking it up, I would be inclined to think a 2x8 rafter and 2x6 rafter tie would work, both at 24OC. Are you installing a ceiling or leaving it open?
Without looking it up, I would be inclined to think a 2x8 rafter and 2x6 rafter tie would work, both at 24OC. Are you installing a ceiling or leaving it open?
Captain Spaulding
Well-known member
Around here, it’s cheaper to get trusses made than to frame it yourself. You might check that before committing to rafters.
billconner
Well-known member
Gable roof with ridge parallel to 18' sides, so 7'-9" rafter spans and 15'-6" ceiling joists, IRC says in for 20 psf live load - least allowed - and 10 psf dead load, SPF no. 2, 24" o. c., a 2x4 spans 8' so fine for your 7'-9" rafters. (And span is based on clear inside dimension - dimension from inside of top plate to top plate.)
Same spacing and species - a 2x6 ceiling joist for drywall - 1:240 - NO Storage at all - is good for only 14'-9". Need to go to 2x8 - 18'-9" - or a different species or spacing. You're good at 19.2" o.c. or #1 Doug fir larch.
Tables at California Residential Code on Up.Codes, down in section R802. I used tables R802.4.1(1) for rafters and R802.5.1(1) for ceiling joists.
Same spacing and species - a 2x6 ceiling joist for drywall - 1:240 - NO Storage at all - is good for only 14'-9". Need to go to 2x8 - 18'-9" - or a different species or spacing. You're good at 19.2" o.c. or #1 Doug fir larch.
Tables at California Residential Code on Up.Codes, down in section R802. I used tables R802.4.1(1) for rafters and R802.5.1(1) for ceiling joists.
Leaflessshadetree
Well-known member
And it only lasted 90 years.
firebirdparts
Well-known member
2 by 6 for everything.
I make everything 16" centers because it's classy. Probably not necessary but that's just what I do.
I make everything 16" centers because it's classy. Probably not necessary but that's just what I do.
Yes! But only with 30 years of sagging.
mike93lx
ALLIANCE MEMBER
We talking about a garage or a person now?Yes! But only with 30 years of sagging.
billconner
Well-known member
I said found and said 2x4 rafters, not 2x10.
billconner
Well-known member
I would go with 2x6 if just rafter ties, and probably every other or third rafter, but hanging sheet rock on them makes them ceiling joists and deflection and cracking the drywall rules.
I'm in the price trusses camp before you commit to building rafters .
I always like that San Diego has it all in one place and includes 4x rafters on their table.
As stated above: 8’ rafter span = 2x4 - but the wood is cheap. Easy to bump up to 2x6.
As stated above: 8’ rafter span = 2x4 - but the wood is cheap. Easy to bump up to 2x6.
Opps! I misread it!
billconner
Well-known member
I usually try to answer inquiry's but fwiw I think I'd use 2x6 rafters and apply sheet rock to them. And use maybe 3 - 4x6s for collar ties. I just like the look of the lifted ceiling and spaced out beefy collar ties. Built an addition for my mil in 80s like this and just saw it was on the market.
Attachments
Are you sheathing the roof with plywood or OSB and shingles or going to do something like a ribbed metal panel ?
Very nice! But, I'm going to keep it simple and boring with a flat ceiling.
rayra
Well-known member
No snow, so why a 6:12 roof?
most rooves in CA are 4:12, btw.
most rooves in CA are 4:12, btw.
TRWham
Well-known member
Current code requires a tie for every rafter.
billconner
Well-known member
Which code? IBC says 4'. IRC does say 24" but also notes "other approved rafter tie methods shall be permitted." So, if this one is to be permitted and inspected, ask the building department or just submit plans showing other spacing. Or ask. If no permit and no inspection, I'd be very comfortable with the spacing I suggested. The addition in photo was permitted and inspected (albeit drive by) and is also still very plumb and level - 40 years later.
And have seen lots of buildings, especially detached garages, with sparse rafter ties. Many fine, some not so much.
Not a purely black and white issue IMHO.
And have seen lots of buildings, especially detached garages, with sparse rafter ties. Many fine, some not so much.
Not a purely black and white issue IMHO.
TRWham
Well-known member
2018 R802.5.2 says "Each rafter shall be tied across the structure with a rafter tie..." 2021 is similar. I have not applied 2024 so not sure if it has changed, but not relevant to us just yet.
billconner
Well-known member
This is what I referred to. Pretty significant when code say other approved rafter tie methods shall be permitted.
2021 IRC
You pulled from this section referring to ceiling joists and rafter ties perpendicular to and above ceiling joists, which may be 2x4s in all cases.
2018 IRC
I just believe a pretty good case can be made for more widely spaced rafter ties, as the IBC permits.
2021 IRC
R802.5.2.2 Rafter ties.
Wood rafter ties shall be not less than 2 inches by 4 inches (51 mm × 102 mm) installed in accordance with Table R802.5.2(1) at a maximum of 24 inches (610 mm) on center. Other approved rafter tie methods shall be permitted.You pulled from this section referring to ceiling joists and rafter ties perpendicular to and above ceiling joists, which may be 2x4s in all cases.
2018 IRC
R802.5.2 Ceiling joist and rafter connections.
Where ceiling joists run parallel to rafters, they shall be connected to rafters at the top wall plate in accordance with Table R802.5.2. Where ceiling joists are not connected to the rafters at the top wall plate, they shall be installed in the bottom third of the rafter height in accordance with Figure R802.4.5 and Table R802.5.2. Where the ceiling joists are installed above the bottom third of the rafter height, the ridge shall be designed as a beam.Where ceiling joists do not run parallel to rafters, the ceiling joists shall be connected to top plates in accordance with Table R602.3(1). Each rafter shall be tied across the structure with a rafter tie or a 2-inch by 4-inch (51 mm × 102 mm) kicker connected to the ceiling diaphragm with nails equivalent in capacity to Table R802.5.2.I just believe a pretty good case can be made for more widely spaced rafter ties, as the IBC permits.