Hi All:
Yet another framing question for you, from Mr. Rank Amateur here:
I’m planning a garage which will share a common wall with an addition. Both will be new construction.
The garage will have an ~ 4/12 shed roof, sloped away from the addition’s exterior bearing wall toward the garage’s exterior bearing wall. Both the addition and the exterior bearing wall on the garage will be conventional 2×6 stud walls bearing on concrete foundations. The plan is to insulate the garage (later, after the building inspectors and tax assessors have gone away) and turn it into my shop.
My question is about the detail for connecting the 2×6 shed roof rafters and the 2×6 garage ceiling joists to the addition’s exterior bearing wall. I’d appreciate your suggestions on a detail which will:
1) Permit me to install this roof after the addition is sheathed and wrapped with housewrap, so I can begin work on the garage AFTER the addition is dried in
2) Permit the shed roof to be properly vented without worries about snow melt/rain leakage at the wall/roof junction
3) Give adequate fire separation to meet the local (Toronto, Ontario) building code, and, of course
4) Give me a strong, secure connection between the wall and the rafters/ceiling joists.
If it weren’t for item 3, I would think that a 2×6 ledger (one for the rafters, one for the ceiling joists) nailed into every stud in the addition’s bearing wall, plus approved hangers with the correct nails, would do the job structurally. I’d need a venting gap (1″? more?) between the tops of the rafters and the top of the ledger board, plus a gap in the roof sheathing for a ridge vent, plus the right flashing detail over the ridge vent (I believe a detail showing the required flashing was posted once before- if I could only get the SEARCH function to find the damned thing for me!). But since this would be a wood-to-wood connection with no fire break, would it give adequate fire separation between the garage and the addition?
I presume an attached garage would need some fire spread control measures, but I’m in the dark as to what the necessary measures might be. Any suggestions on what I might be in for? Drywall over the addition’s sheathing along the adjoining wall? Double drywall? A self-closing fire door between the attached garage and the addition? Ceiling drywall whether I want/need it or not?
As always, your suggestions and ideas are GREATLY APPRECIATED!
Replies
Hey Molten,
Roof ventilation and fire blocking are diametrically opposed concepts. One encourages airflow and the other prevents it.
The only way I can see to accomodate both requirements is something like:
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SamT
Thanks, SamT. Your detail would work structurally and ventilation-wise, and wouldn't rely on one of those baffled ridge vent products- with the higher baffle height, it would probably resist leakage from melting snow a lot better too. But you're still nailing the ledger to the exterior wall. Structurally I'm totally ok with that (providing the code inspector is too), but I'm just worried that there's some fire separation rule I'd be violating by tying the garage roof to the wall this way.
I was hoping that somebody would be able to comment on the fire-spread stuff from a code knowledge standpoint. Damned codes- if they're going to become part of what amounts to government regulation, and they want everybody to know what's in 'em, they should be available for free to whoever needs them- not sold for $200 every few years! Aside from asking you guys who might happen to know off the tops of your heads, my other option is to sit in the local public library and wait my turn for the ONLY copy they have in the reference section...
So I ask again: what are the code rules regarding fire separation between an attached garage and the house, if any? Or are they just considered parts of the same structure, so framing I would get away with anywhere else in the same house is just fine?
And if anyone can find the detail showing how to use one of those low-profile baffled ridge-vent products in this geometry and re-post it or give me the link, I'd appreciate it! I dug through at least 50 posts using the search function and was unable to find it.
Molten,
The basis of the firecode (I don't have it in front of me) is the provide a time for occupants to exit. It tries primarily to prevent any drafts from one side to another for that time.
Run this detail pass your inspector and see if he will pass on it.
View Image
Note that the firestop DW runs up to the metal flashing on top of the vent material, and the flashing is set in a bead of fire caulk on top of the DW.
The rafter hangers (ape hanger type) are one size smaller than the rafters. This gives a 2" gap for ventilation.
You can wrap the bottom of the ledger in firestop or use wedges shims to extend the bottom horizontally to meet the rafters. (ceiling)
The inspector will probably allow you to stop the sheathing at the top of the firestop DW to economize, if you fire caulk the joint.
Hope this helps you with ideas,
SamT
M,
Try a detail that would allow a layer or 2 of 5/8" firerated drywall on the garage side of the framed wall for the separation. Install a bolted on steel angle or channel as the ledger support for the roof rafters. The steel can be connected to the wall studs directly, with the FR sheetrock butted up to it. FR sheetrock on the underside of the roof framing will also slow the spread of fire from the garage to the house. Skip the ceiling joist if its to be a shop area. You'll be glad for the additional head room.
G_ranch
Great idea. Question, though- how would you attach the rafters/joists to the steel ledger? Would I have to drill holes and bolt them down? And if I did a steel ledger for the ceiling joists (need 'em for a place to stuff insulation later- gets cold up here in Canada), would I need to do one for the ceiling joists if I put a double layer of sheetrock on the ceiling itself to act as the principal fire separation? Guess that's no good if the fire starts on the roof of the garage from sparks from the burning house next door, but that's getting pretty picky, isn't it? Problem is, I don't know WHAT horrible things the code guys have imagined...
One option I'm considering is using I-joists to do a cathedral type ceiling, rather than using separate rafters and ceiling joists. Guess I'd have to bother the I-joist guys for an attachment detail for both ends that works with their particular product. Any hints what this might look like? My framing book is pretty scant on steel details.