I haven’t framed a roof in a long time, and started one last night but had one heck of a time figuring ridge height. It is a gable roof, 12″ span, 6′ run, 4/12 pitch. So i figure ridge height should be 24″ . I cut a block 24″ minus ridge with and place ridge on it a go to set rafters, too short. So i think maybe i have to add in the width of rafter, do that= too high. It was getting dark so i knicked out block and nailed it up with the rafters. I seem to remember there being a formula for figuring ridge height but cannot find it in any of my books. I seem to recall the birds mouth coming into play here. I do have the rafters cut right, so that isn’t my problem. Any help would be appreciated, thanks guys.
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The top of you're ridge is going to be @ ~24" above the plate BEFORE you figure in the addl heights for birdsmouth cuts AND depth of lumber.
Edited 4/18/2009 8:21 am ET by john7g
24" plus the "height above plate", which is the distance measured plumb up from the bird's mouth to the top of the rafter. You can use the formula or just draw your plumb line up from the seat cut and measure it.
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Thanks mmoogie, I thought the HAP had something to do with it but couldn't remember.
One minor detail...HAP plus 24" is to your theoretical peak. The top of a 2x ridge would be about 1/4" lower than that because the peak is missing on the edge of the ridge.Steve
I thought the HAP had something to do with it but couldn't remember.
It's the HAP and 1/2 the thickness of the ridge that you need to figure the ridge height, if you want to know the math. 24" plus the HAP height is not the ridge height. Nailing the front and back rafters up at each end first and lifting the ridge between them sets the ridge height with no math at all.
Joe Carola
Edited 4/18/2009 9:01 pm ET by Framer
Framer I had to use a brace, the ridge was two pieces and i needed something at the joint and on the gable end for my "helper" to set his end on while i nailed the rafters at the joint. My question is what do i do with the HAP and half the thickness of the ridge to figure out the height ? Thanks
What size rafter and ridge are you using? Are the walls 2x4 or 2x6?
Joe Carola
Edited 4/19/2009 6:21 am ET by Framer
2x4 walls, 2x6 rafters, 2x10 ridge i didn't buy the lumber and the helper (his shed) shows up with 2x10 and said it was cheaper than 2x8 so i used it.
Joe, you aren't supposed to give them all the secrets!
front and back rafters up at each end first and lifting the ridge between them sets the ridge height with no math at all.>>>>>>>>>>>>>
You forgot to add the height of the heel...which is probably 4 1/8".
You also calculated your rise incorrectly. If you have a 6' theoretically run, you need to subtract half the thickness of your ridge, which is probably a 2x8, so you'd need to subtract 3/4".
Your actual rise, for purposes of determining ridge height would be 71 3/4" if my assumptions are correct.
So the math looks like this: 71.75 / 12 x 4 + heel . This gives you the top of your rafter. Don't be afraid to drop the ridge to accomodate a ridge vent.