6:12 pitch.
Want to run a double 2×12 ridge horizontally about 10 feet beyond 20 foot wide gable end, running double 2×8 ‘subfacia’ from the end point of the ridge to the corners of the gable wall to carry the bottom end of the rafters under the roof that’s extending beyond the house.
Northern Ontario, like that’s in Canada eh!, so there’s like snow loads for sure eh!
Let’s not confuse the issue with facts!
Replies
The second half of your description doesn't compute. Do the 2x8 members run diagonally from the ridge back to the wall, resulting in a triangular overhang when viewed from above?
...triangular overhang...
That's what it sounds like to me.
Anyway, Art's got it right. 10 feet is too long for a 2x12x2.
Sounds like a job for Captain Knee Brace.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
10 feet beyond
no
I cannot imagine even guessing on this one. You need an engineer.
The only guess I have is that, besides doubled 2x12 not being strong enough, 10 feet of cantilever means that you would need them to be, oh, maybe 40 feet long and one continuous piece.
4 feet deep of snow cantilevered out 10 feet? Egads.
By the time you spec the ridge beam strong enough (I'm thinking a big parallam beam at the least), snow load is gonna lever the other end of the house off it's foundation. (he said only half-jokingly)
Your roofline sounds like an exaggerated version of a Viceroy Summerhill.
Regards,
Tim Ruttan
Tim,
It isn't that bad; this is called a 'swiss rake' around here and it's fairly common. The way this is usually framed is with big knee braces on the gable wall--one at the ridge and one (or two, depending on the length of the roof pan) each side lower down. The rafters die into the angled rake board, and sit on the top arms of the knees. Sometimes guys frame lookouts between rafters, too. The soffit is generally left open, and the roof is decked with 2x4 or 2x6 T&G.
But yeah, he should have an engineer draw it up for him. Not the sort of thing he wants to be guessing about.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Yes the picture is similar, though smaller in scale. Trying to extend the original roof over an added porch. Original is apparently an 'Aspen Chalet' kit - double 2x6 rafters 4' oc with 2" thick t&g roff deck boards.The 10' overhang comes from mimicking the overhand on the other end, but the other end is only 12' wide ergo only 6' of overhang.Guess I could mightly tone down the angle of the rake boards to foreshorten the overhang a lot.Knew it didn't pass the smell test.Let's not confuse the issue with facts!
Guess I could....
Don't guess; let your engineer apply his nose to the 'smell test.' That's why his nose spent all those years applied to the university grindstone, LOL.
There's usually a reasonably potable way to do these things but it's hard for us out here in webspace to pinpoint the one that suits your situation best.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Your 'cantilever' wording threw me initially, it is not as bad as it would be for a 10 ft cantilever.
Just back of the envelope the 2-2x12s are ok: however, what is lacking is rigidity against crippling in the 2x8 facia boards. Doubled 2-2x8s nailed to 3/4 ply roof sheathing should be able to hold. Securing both ends of the 2x8 needs about 4 ea 1/2" carriage bolts and solid framing, not just nails.
A good test would be to build it, put a chain over the end of the 2x12s, and lift a 7000# truck off the ground without anything pulling loose.
This advice is worth exactly what you paid for it, zero <G>
Thanks junkhound. The real test would be getting a 7,000 pound vehicle to the site for a test. It's boat access only. I guess if I lived there I could drive over some winter when the ice is a good 3' thick.Existing half hip roof rafters span 8' and are 2x4's and luckily have withstood every winter so far. Just looking for more room in the porch and trying to keep the 'integrity' of feel of the existing camp roof.Let's not confuse the issue with facts!
Dino, I see it in Ontario cottage country, without the knee braces (which obviously would make a big difference, assuming you properly transfer the load). And the OP never mentioned knee braces.
So, 10' of triangular overhang with moderately heavy snowload and no knee braces? Sounds like a Parallam ridge beam running the length of the gable to me. As you suggest, actually sounds like 3, with 1 on each slope halfway down to cut the rafter span. I'll allow that the midpoint parallams might be a little more petite compared to the ridge, although they'd probably be spec'd to the same size for visual continuity. And they might not have to run the length of the gable.
If the OP gets an engineer, I'd like to know what the solution is. I'll guess 3.5"x14" Parallam. But maybe I'm way-overengineering and he'll only need 3.5"x11.875"... :-)
Regards,
Tim Ruttan