Help with connecting wrap around porch roof at hip.
BGT_Masters
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Without going into a great detail of rambling that will only get things complicated I am just going to post what I am trying to do and measurements and hope someone can figure out how to do it.
I have an existing deck with a roof in the front of my house (which is a rectangle). The deck is 9 feet. The roof over it measures roughly 127″ x 38.5″ x 132″. I want to wrap the deck and roof around the side of the house but I want the new deck to be 12′ instead of 9′. This is causing me issues figuring out how to do the hip.
The clearance/head room from the bottom of the rafter support header board is 85″ from the deck itself.
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If you want to maintain the same pitch with the new roof and header height, the ridge height on new roof will be 3’ of run higher (12’ of run on new deck minus 9’ of run of old deck is 3’ difference). Cut the hip at the 12’ of run, it will attach on the new higher ridge. The hip will not meet at the corner of the house it will be set in from the corner to make up the 3’ difference of run, so you’ll have a jack rafter nailed against wall on higher ridge side of house to allow plane of old roof to extend beyond the corner of house to meet the new higher ridge. If you want the header and ridge lines to match you have an irregular pitched roof with a hip that doesn’t run at 45 degrees. I would need to know the the roof pitch of existing roof to figure all that out, it gets complicated and if you’re having a hard time wrapping your head around the same pitch idea, the irregular will make your head explode.
The current pitch of the existing roof I am trying to tie into is 3.638/12. If I am understanding it correctly, the problem with the difference in height which I believe was something like 10.5" however there are two windows which sit about 5 inches above the current rafter ledger line. And would more than likely be in the way.
Ugh. Jlyda has you on the right path. With the new information it’s going to get really tricky. I am not sure your going to like any of your choices. Without doing the math you can;
Keep the same height and not have enough pitch to use shingles.
Keep the pitch and have to tunnel out the windows.
Keep the 9’ depth
Well tunneling isn't an option, and though keeping it at 9 feet all around would be easiest it would defeat the purpose of needing more room on the added decking.
This might help. The house wrapped part in front is half of the porch/deck that I enclosed the remaining front porch deck is out of screen on the left. I want to wrap around the side of the house and back of house 12 feet, instead of the 9 feet that the front comes out. In the picture there is only one window on the side of the house but there will be another window of the same size going in next to it further down.
If maintaining the ridge height to accommodate windows you’ll have an irregular hip and different pitch on new roof. I’m assuming the old roof is actually a 4/12 pitch? With the 4/12 pitch, the total rise is 3’ at 9’ of run. To make up 3’ rise in 12’ run of the new roof it will be a 3/12 pitch. The irregular hip will not sit at a 45 degree angle and overhang length will differ from existing to have fascia line up. The hip will attach on top at corner of the house, but the seat cut on hip will not sit perfectly on the corner where the 2 headers meet (the hip angle isn’t a 45 degree angle). If you want same size overhang you’ll need to drop the height of the header on new. You can maintain the header height on underside of header by ripping top of header to accommodate the drop. Or you can change the HAP (height above plate) measurement on the new rafter. The good news is that 3/12 and 4/12 aren’t that far apart, so all the accommodations for the pitch irregularities are minimal. Typically, there is more of a pitch difference with irregular roofs, so one side of jack rafters will actually set a little high on top side of hip (unless you cut a bevel on top of the hip). The angle difference between 3/12 and 4/12 is so close you shouldn’t have to worry about it. The measurements I provided assumes the old roof is a 4/12. If not, the pitch of new roof changes a little. I’m assuming you used a level on an existing roof rafter to determine pitch? That tends to not read true, but will get you close. The best way to determine the pitch is to find total run and total rise. Also, I don’t know many carpenters that would choose to cut a 3.6/12, so assuming the roof is 4/12. If you don’t have a lot of experience with irregular roofs or you don’t feel like messing with the math I would suggest the string line method. There’s been a few articles in FHB about how that’s done and probably some info online somewhere. It’s not as quick to install as the math method (if you know how to do the math), but gets the job done. For the string line method you’ll basically build the roof as far as you can w/out installing the hip. Using a straight edge or string lines you can plane new and old roofs together to find intersection point of hip on the header. From there you can string the hip to find measurements, side cuts and etc. Also, when shingling lower than 4/12 you need to install shingles in low pitch method. Shingle manufacturer will instruct on that. Hope that helps.
I finally got some time to grab some better measurements I used a string and a level attached to it this time. It does measure more towards a 4/12. Measurements differ slightly from one side of the front porch to the other. Here is the side we would be working off. The rise is 40", the run is 126" and the rafter length (which included ledger board) is 131. Which is 3.952/12.
If I needed to I could always pull out the window on the side of the house and replace it with one 7-8 inches shorter? The current window clearance is 7" from the roof line. Then just have my hip peak somewhere on the side of the house and have the ledger board higher than it is on the front?
Doing the math as if the run were a perfect 9’ on old roof and perfect 12’ run on new roof while maintaining a 4/12 on new as well, the new ridge will be 1’ higher than existing, so can use that to determine size of window. Your hip will sit off of corner of house as I described before. To keep it simple (wood is cheap) cut an extra common rafter at the new roof dimensions and install the rafter on the old roof side. So it will appear as if you installed a rake board on old roof and left it long on top, continuing up higher from existing ledger along the wall. You can butt your new ledger ridge right against that. The point in which that rafter and new ridge meet will be where the new hip (cut at 12’ run) will be placed.
I already did that earlier with string and I got only 8 inches in extra ledger height. I ran the string up 36 inches up the side of the house following the slope of existing roof. If you look at my photo it came an inch above the bottom of side window and maybe 6-10 inches (I’d have to look) to the left of window. Does this sound right or at least plausible and not a full foot? I know it’s not exactly a 4/12 but I’m off a full 4 inches from what a 4/12 rise should be with a 3’ increase in run.