How To Fiqure Roof Pitch?

JPV123

What's the formula for fiquring out roof pitch? I'm trying to get an idea of pitch for a screen porch roof. The height where it will attach to the house measures 11' 9" (from the existing deck to the bottom of a window). I plan on going out 12'. I would like to have an 8' opening at the edge of the deck. So I will be going from 11'9" height to 8' height over a 12' span. Thanks for your help.

Paulsan

11'9" - 8' = rise.
12' = run.

Teetorbilt

JPV, just perzaktly kind of GC are you?

__________________
You can't solve you're problems with the same level of thinking that created the problems.

Albert Einstein

JPV123

We do alot of interior remodels. 3rd floors, basements, kitchens, baths, We also have done alot of decks and a few sheds. I've had plans drawn for the porches we built so far and on the sheds my framer would usually cut the rafters to get the pitch we need. We are now starting to bid a few more screen porches and a possible small addition. I want to make sure I have a 12:3 or at least a 12:2 since there is a window that limits the height of my ridge board.

River Rat Dad

"I would like to have an 8' opening"
Is that head room? how big is the header? How big are the rafters? How deep is the birdmouth?

Is the 11' 9" the bottom or top of the rafters? To figure the pitch you can't mix and match.

JPV123

The 11'9" would be the top of the 2x8 rafters. the 8' is "headroom" as in the bottom of a double 2x10 header. As deep of a birdsmouth as code would allow so I can get the most pitch.

Alan Hughes

Glasshousebltr

It's just short of 3/12 if your rafter tail sits on top of your 8 ft mark.

Maybe you need to get your framer out there before something goes terribly wrong.

Also BTW, the board on the wall just under the window is called a ledger, a ridge is only used at the peak of a roof joined.

Bob

__________________
Bob

IHI

Actually pitch comes out to 3 3/4 so it's just short of 4/12 calculator never lies so long as user has head outta his azz

__________________
Hot Rod Work Van
Car video clip
Web
The Photo Gear- Type Josh into Contact name when ordering

Glasshousebltr

if the tail sits at the 8ft mark and top of the the ledger sits at 11'9, with a 12' run the rise is 3' 1 1/2" making it a hair over 3/12, sorry my bad. Don't know why, but my first figure was on a 10" rafter.

I think you forgot to deduct for your rafter width IHI.

I think if ya cut your birds mouth and plumb cut right at 3, the ledger and exterior wall width hits ya darn near right on target.

If ya feel like your wanting to build a piano, take your seat to 4 1/2 on the birds mouth. As long as the ledgers right at 11'9 and the walls are plumb and at 8', 3/12 will suck up to the ledger nice and tight.

Oh yea, this on the assumption of a 2X ledger, which happens to be a good move anyhow.

Bob

__________________
Bob

Grumpy

If you can't have a 3/12 pitch, and it has to be lower, this isn't a problem just switch out the roofing material to modified bitumen. Roofing is flexible like that, there is always an alternative, if you know what they are.

Another alternative is building up any pitch you desire, but then building a "pan" under the windows, and lining the pan with metal, either copper or galvanized with soldered seams.

IHI

I did'nt the calculator did It'd have to be one VERY specific plan with other details being affected to lose sleep over the 1/4" +/- one way or another anyways At least it's still within spec to install a shingle instead of going with a membrane so that's a plus.

I hate roofing and hate framing roofs-especially hips/valley's, seems I tend to make the first few pieces into "voluntary" firewood LOL!!

__________________
Hot Rod Work Van
Car video clip
Web
The Photo Gear- Type Josh into Contact name when ordering

Alan Hughes

me too.

JPV123

OOps I said ledger but typed ridge. That shows you the type of week I had

JRM22

The best way to determine pitch is to allow 4 1/2 for rafter , take the distance from top of ridge or ledger to top of rafter . If the bottom of 2/10 header is at 8ft then you have to take off 9 1/4 for header and the 4 1/2 left in rafter .

BamBamm5144

Hopefully he figured this problem out already otherwise it will have been over 5 years of thinking about it.

MALCO.New.York

The Devil is in the Details!

__________________
Something to One may be Nothing to another!

Ultimate Wisdom---------
http://www.youtube.com/watch?v=OW-cnizLDEE