Align soffits/ roofline on roof addition
Hello everyone.I am in need of some advice/guidance.I am building an addition to my existing home. It will be a 12×12 sun room.The existing gable roof is made of engineered trusses (2×4) , 24 o.c., 5/12 pitch.The addition will have a gable roof, that will be perpendicular to the existing roof. I plan on framing it using 2×8, 16 o.c for rafters, with a 2×10 LVL for a beam, cathedral ceiling.The problem that I am having is trying to figure out how to line up the soffits, so they are in the same plane.I figure I can adjust the pitch of the new roof, raise/lower the wall, or adjust the cut for the bird’s mouth. I would be okay if the new soffit is not the same size. I am not sure what would be the best/easier way to achieve this.Thank you for any input.
Replies
How wide are the soffits?
Hi Dan,
Thank you for your time. The house soffits are 12" wide.
Well if you current soffits are really 12" on a 5/12 pitch then all you have to do is get a square hippopotumus and figure it out.
Soffit should fall five inches below the top plate of the wall plus the depth of the birds mouth given you want a run of 12" on the soffit.
Your rafters will be almost 92"
Thats the mathmatical answer I think
But you could also just frame the thing at the five twelve pitch, let the rafter tails run long and then mark them with a level off the original soffit.
All of this assumes you make the new wall top plates line up with the old wall top plates whether or not your floor will be level.
You're sure it isn't a rhinocerous?
cyp
If you have the floor framed for the addition-and no walls.............
Go out and make a mock up right on the deck-full size. Should be able to figure it out being able to see it.
Draw your house frame (roof pitch, overhang, wall plate location) then in the same plane-draw your new frame. Working backwards to the floor line of the new addition will tell you if you need to shorten the walls, adjust the birdsmount (not too much so it's wrong and won't pass inspection) or simply by clipping the bottom of the rafter tail.
Let them run long...
"I would be okay if the new soffit is not the same size. I am not sure what would be the best/easier way to achieve this."
Since you're not overly concerned with them matching perfectly, probably the EASIEST way to get the job done would be to do your basic framing calculation regarding roof pitch, HAP, etc, and frame the roof that way. That way the siffit and fascia will be close. But instead of cutting the rafter tail plumb and seat cuts prior to them being installed, install the rafters with uncut tails and let the tails run a bit long. Meaning, cut the ridge plumb cut so the rafter will mate to the ridge board, cut the birdsmouth so the tail end will sit on the top plate, but do not cut the rafter tail to length.
Then after the rafters are up, you can reference your existing soffit and fascia and then snap lines from one end rafter to the other end rafter, and cut the new rafter tails to match the existing soffit elevation and/or depth. Don't forget to allow for any subfascia or soffit skin materials.
You can also adjust the length of the overhang to keep the same fascia line if you like.
But - The math is pretty easy.
A common truss at 5/12 has a heel roughly 4" tall. So you're 4" above the plate.
Go out a foot at 5/12, and you drop 5". So the fascia line is 1" below the plate line.
Go back in a foot from there at 12/12, and you're 11" above the plate line.
The plumb cut of a 2x8 is roughly 10" at 12/12, so you'll have to build your plates up a bit or increase your rafter size.
BossHog,
Would I have to build the plates up, or lower wall?
Build 'em up.
Get a good roof framer
BossHog wrote:
You can also adjust the length of the overhang to keep the same fascia line if you like.
But - The math is pretty easy.
A common truss at 5/12 has a heel roughly 4" tall. So you're 4" above the plate.
Go out a foot at 5/12, and you drop 5". So the fascia line is 1" below the plate line.
Go back in a foot from there at 12/12, and you're 11" above the plate line.
The plumb cut of a 2x8 is roughly 10" at 12/12, so you'll have to build your plates up a bit or increase your rafter size.
I am not sure I understand all the math but my roof framer did it on a piece of plywood with a pencil and his framing square. I had a similar problem with a 4:12 hip going onto an existing 2.5:12 roof. It was amazing for a guy who can't even spell trigonometry. Everythong lined up when he was done
BTW the engineer at the truss company screwed it up and the valley trusses I bought didn't work. My framer started from scratch.
"...the engineer at the truss
"...the engineer at the truss company screwed it up..."
They aren't engineers. They're just uneducated guys like me. And like any other profession, some are good, some are worthless, and everything inbetween.
Thanks guys for taking your time to reply!
I guess I just have to get a pencil, square and level and just do it.
One more question. For the ridge beam, I was thinking a 2x10 LVL. Do you guys think it would be enough for my length, 12", or should I double it up? I live in central Wisconsin, so we tend do get some snow. For roofing, I would be using the architectural shingles. I thought I would keep the same pitch, or increase it to a 6/12.
Thank you again!