Hi, I would greatly appreciate any advice! I want to rip off this flat leaking porch from the 1950s and add a gable roof with a 7/12 pitch. But I’m having trouble visualizing how the new gable roof would attach to the existing roof on both sides so I don’t have a flat valley, where water doesn’t drain. The dimensions are 10ft X14ft. Thank you.
The end of this program will likely lead to higher energy bills and fewer business opportunities for the American people.
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
Why 7/12 pitch roof? The roof in the pics don't look that steep. You can do what you suggest, but you will have to deal with the water in the valley, created by the added gable roof, with a cricket. The cricket will be like a low pitch roof. There might be other options, but would envolve major framing changes. At least that is my take on it.
Good luck!
How about replacing the leaking roof? Or try sketchup to see what can be done. After playing with the design the flat roof might look really good!
Thanks for replying. I've been using woodcraft, a 3D auto cad program on the iPad. The gable roof aesthetically looks the best. I'm also going to be building a deck over the existing concrete porch, which is easy. So there might be a lack of headroom if I replace the roof. Maybe I could install a small cricket roof along side of the gable roof to promote water drainage?
The only thing I can think of is to make a low-pitch prow-front gable on a 45. The valleys would still be problematic, though.
Right side up.
Thank you!
You've got a problem if you want a gable. It could be done but you'd need to modify both of the existing gables to make it work. Your new gable will have to butt into one of the roof pitches that are already there. If the new roof is higher than the old roof the far side of the old roof will have to be exteneded to the ridge of the new roof. No big problem there. But you're still left with the parallel gable. Leaving a blind valley between them is a terrible idea so the only thing left is to raise the ridge of the new gable to a point in the same plane as the existing gable. The opposite side of the roof would then extend in a flat line to your new ridge.
Unless your budget is unlimited I think this is out of the question. If it were my house I'd put down a good roof material and call it a day. You could get more pitch by extending the back of the flat roof up the adjacent pitches several feet. Still a lot of framing but you'll get the water off the roof very quickly.
Ditto
We have a remotely similar situation on our house. Rather than do extensive framing to create a pitched and more attractive roof, we opted to be practicle. So, during a whole house re-roofing, we had a pvc membrane installed over the flat roof. The guys ran it well up under the adjoining shingles. No leaks and no worries. The roof is still not very attractive so we simply divert our eyes.
Good points!
Thank you for the advice. I will rip off the old porch because of rot and create a new overhang like you suggested by extending the back of the new roof several feet. But the two intersecting roofs are different pitches. 7/12 and 5/12. Would I lay out the rafters like I would when building a gable roof?
You'd going to raise one end of your shed roof by extending it up the slope several feet. nail down a 2 X 12 at the high point and nail your raftewrs to that. The cut will be the reciprocal of the pitch. so it will be a long cut. Lay the rafters out just like you would on any roof and get as close to the other roof as possible. At the point use a straight edge at the top and the botttom to extend the shed roof line to the other roof, Run a string between those points, measure down to the roof and cut your last rafter to that measurement.
I'm getting there!
Thanks for all the advice. I did some demolition today and found the 2x4 rafters, 2x10 beams are relatively still in good condition. I jacked up the porch roof about 5-6 inches, because the foundation has settled. Everything is plumb now. The roof sheathing is 1x6's, with some rot in a few places (along gutters, and at intersecting gables). So I'm probably going to replace all the sheathing with OSB or Plywood. There is a felt or rubber type material that is on the roof. With a low pitch roof, what is the appropriate roofing material and flashing that you recommend? Thank you, and have a happy Memorial Day weekend
Take off the shingles up about 24 inches on borth sides so you can run whatever membrane you use up at least that far. if you have heavy snow I would go even higher. There are lots of peel and seal membranes that are easy to work with since they come in short rolls. Roll them out across the roof and continue across the valley when you get that high. At the botom corner put a kickout flashing to divert water away from the house. I'd also use drip edge on both outside edges. Roll out a base layer than a top layer. Once they are down run your shingles back down to the original position.
You can also use EDPM, probably what you have now, but it's not a one man job and is much harder to lay then the self sealing membranes.
4/12 pitch?
Could I add a 4/12 pitch to the top of the existing porch roof? That way I can shingle it and not worry about leaking. How would I find the cut of the new rafters that attach to the 7/12 and 5/12 existing roofs and porch? Thanks
Sure. Your rafters will only butt to one of the two pitches and run parallel to the other. Running up the 7/12 will give you the shorter rafters but it won't matter. The big chice inmy opinion would be the appearance. As a matter of fact you could run your rafters all the way to the ridge and your porch roof would then appear to be part of the original roof.
Rafter cut angle?
Never thought about running rafters all the way up, those would be some long ones. Good idea! Sorry for asking all these questions, but how exactly would I find the angle of cut for the head of the new rafter with a 4 or 5:12 pitch? I know it would be a long one, like you said before. I was never good at math but I do have a CM pro Calculator. Thanks again.
I hate to admit it but I'd probably use trial and error on a cut like that. You could also put a knee wall somewhere in the middle for additional support and to allow smaller rafters. I think I'd turn the roof and run the rafters up to the lower ridge which will give you a new valley higher up the 7/12 roof.
Birds mouth?
Instead of trying to figure out the long cut. Couldn't I cut some of the sheathing back on the existing roof and tie my new rafters into the old rafters of the house and build a knee wall? My new rafters are 16ft long. I want to match the eave of the new roof to the old, which is 6"3/4. I'm having problems laying out the birds mouth. The new rafters will sit on 2 2x10s. I think my pitch will be 2/12. Still a lot better than 3/4"/12. Thank you
You can get away with anything the building inspectors won't see but my engineer always has us nail a 2 X 12" to the roof for the rafters to sit on. With a pitch that low I wouldn't worry about a birds mouth especially if you're going to clip the rafters to the plate. But why not go up some more and get up enough that you can use shingles?
I have no idea how to milk a 3-D rendering out of SketchUp, so here is a plan view of the "prow front" idea I mentioned earlier.
Basically you have the two intersecting rooflines, and coming off from near the intersection of the two ridges is the ridge of the porch, running at about 45 degrees. The porch ridge maintains an even height for its full distance, and two valleys are formed where the porch roof slope intersects the slope of the main roofs -- these are the two not-quite-45-degree lines.
With a timbered treatment of the trusses supporting the "prow", this would produce a striking architectural feature. Even with a simple clap siding "gable" I think the appearance would be pretty good.
(But someone really needs to produce a 3-D rendering of some sort to reasonably judge the appearance.)
I think it would look better if the ridge of the porch roof intersects the existing valley, but it may not if the porch roof becomes too asymetrical.
Yeah, I don't know how the fine points would work out best. You'd almost have to build a scale model.
I think I might take the easy way out...
Could i add a 4/12 pitch on top of the existing structure? That way I could shingle the new roof. How would I cut the new rafters to sit on the 7:12 and 5:12 existing gables and old porch? Thank you.
Your first sketch made it a hip of sorts. I had in mind a gable end, with the ridge running horizontal.
Well, I'm not sure what the OP wants or even has. It was good practice for me with Sketchup. I'm not good with it at all, and I have poor spatial imagination to boot.
uhhh this maybe?
I appreciate the effort, but not what I had in mind. Basically, take your first (no number) design but raise the ridge up so it runs horizontal vs sloping down. Something like this (only the area under the porch roof would be open).
That's pretty cool looking, but sort of odd. I'm thinking the OP wants a steeper gable. I don't see a clean way to do that. I wish I could find a free way to make 3d pdf files. I don't know if the OP has looked at the drawings. At least you posted a thumbnail to preview.
Imagine the gable with open timbered trusses.
I'm not too good at imagining,. It wouldn't be good at protecting from rain and snow unless it was closed in behind the timbers. I'm not a big fan of timbers anyway myself, unless they are on a big lodge, or on a very rustic style building.
Doesn't have to be timbers, of course. Could be a clap gable, or you could make it a hair decorative with diagonal claps.
I would just keep the existing look, I don't think it looks bad. Maybe use a copper flat roof, or epdm. Oh well, it's fun to play with sketchup, but I never have made a nice drawing with it.
The gable would look like this.
Although it doesn't show an intersection with existing gables, the gable of the addition would look like this.