Tying in Addition Roof
I’m having trouble finding definitive answers on how to tie in my additions roof.
The home is a basic ranch roof, no dormers on the addition, just a straight roof. I’ll be tying the addition into the gable end of the existing home using the same roof pitch and truss design for the most part.
-Should I just snap a line and cut the eave, including shingles and fascia right off? I know the fascia will have to go to get the new truss in at some point.
-Do I need to weave in the plywood to the original roof if there will be a new truss sistered up to the gable?
-Should I start with the sistered truss first rather than the gable end when setting the trusses? I could cut some holes in the old gable end and use the old roof trusses as support when starting my bracing as well.
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Replies
Mike,
If your aim is for the roof slopes of the addition to be co-planar with the roof slopes of the original house, you're facing a challenge. It can be done, but it's trickier to do than when the roof slopes of the addition are higher or lower than the original roof.
Yes, cut off the rake overhang.
You had better hope the slope of the new trusses exactly matches the slope of the old roof. That's tricky.
Yes, cut back some of the roof sheathing so that you can weave a few panels of plywood, joining the addition to the old house.
Keep a bundle of cedar shingles handy to use as shims -- you'll need them. It's hard to avoid lips and bumps. For a subtle shim, you can use asphalt felt, folded multiple times as needed.
Yeah, if there's any way to make a transition I'd do it. Different age, different material, different construction - It'll always look different, could make the roofing at the transition wear poorly. Can you tuck the new roof a few inches below the overhang of the old roof? Enough to allow you to step flash the new roof to the old house?
The trusses were made by the same company from the original trusses. I had the old drawings and they came out twice to measure. Hopefully they did a good job.
I could possibly tuck it but the overhang is not enough to hit the next truss. I would have to add bracing the entire length to be able to nail the edges.
I was thinking since the end would be completely supported by a new truss, I wouldn't really have to pull back pieces of plywood. I could always pull back the shorter ones, but this still adds a lot of work, and will still not have the correct O.C. measurement unless I set the second truss 24" from the center of the last original truss.
Mike,
I suppose weaving some of the plywood roof sheathing is optional. It's up to you.
Like Dan, I'm worried that shrinkage of framing lumber will eventually reveal differences in elevation between the two roof planes -- and that the line will telegraph through the shingles.
I did what you are proposing on a job 30 years ago. It still looks OK, fortunately -- but I was very conscientious when I shimmed the roof sheathing, paying close attention to the need to keep the roofs co-planar.
It looks like they ended up close to a half inch difference in height. I would say I could notch the top plate to make the roof even, but that would also require me to mess with ceilings, especially in the room that will occupy both the addition and original home. This would also a large amount of work.
I think I'll try to shim the first few feet so the elevation change to the new roof is more gradual. What amount of variation is not as noticeable with architectural shingles? I would assume that three tab would be harder to conceal than these.