Starting in on my first dormer project. It’s a shed dormer about 10′ wide basically giving head room inside for a second floor bathroom. We’re all permitted and planned out, and the thing I’m trying to figure out is the intersection of the dormer roof and the existing roof.
I’m not sure how far back to pull up the existing asphalt shingles in order to frame the intersection of the new roof to the existing sheathing. The same issue applies for the intersection of the side walls and the existing roof. I’ll cut my opening to the size of the inside framing (a little extra so there’s no futzing around). But should I then pull up a few rows of shingles in order to get all the framing attached to the sheathing and then work new shingles and step flashing back in?
And where the barge rafter meets the existing roof seems like the critical juncture that I end up fixing on most other dormers, so I want to make sure that I’m not forgetting anything when I start from the beginning.
So any advice, no matter how simple or redundant will be helpful.
Thanks, Paul
Replies
Paul,
Sounds like your dormer rafters aren't going up to the existing ridge. You still have to remove the existing rafters and put a header in between the existing rafters to catch the dormer rafters. Tearing up enough shingles isn't what you should be concerned about, that's the easy part.Just go high enough to get it framed in and keep water tight. The roofer will have to pull up what he needs anyway. How are you framing this?
The side walls either sit on the floor that have supporting joists underneath them, or they have to sit on double up existing rafters.
Yeah, I forgot to mention that the dormer roof starts about 2 feet below the existing ridge. There is a header picking up the cut off rafters. The side walls continue down to the floor joists below (and a new steel beam that had to go in because the dormer sits midway above the open kitchen span below)
Framing wise it's only sitting on 2"x6" floor joists below with 2"x3" stud walls up to the existing ceiling. So I put in a steel beam in line with the 2"x6" floor joists that spans to 2 bearing walls, then a 4"x10" beam that spans perpendicular from that steel beam (bearing on top of it) out to another bearing wall. The front of the dormer bears on the 4"x10" beam (2"x6" stud wall framing). The header picking up the existing rafters will be 4"x6" and bear down on the steel beam on one side and the interior bearing wall on the other.
The dormer rafters are 2"x8"s and the ceiling joists are 2"x4". Everything was planned out and the city wanted the steel beam added in place of a 4" glulam.
That's about what's going on for the framing. I was thinking I'd have to cut part of the roof open to drop in the steel beam, but it was much lighter than I thought (80 lbs, instead of a couple hundred)....So I was able to open the walls up and slide it in with only a little futzing around. I'll be doing the roofing myself, or at least the flashing and drying in. The homeowners might do the shingles themselves.Paul
Do your self a favor and box the end of the soffit closed at the nook where it gets impossible to get flashing and shingles back up under there. Just as far out as the fascia is wide, where it meets the main roof.
Slip flashing behind the fascia, an apron on the box face, then your steps goinf down the dormer cheek...
That keeps all the critters out hopefully.
Spheramid Enterprises Architectural Woodworks
"If you want something you've never had, do something you've never done"
I think I'm mostly with you on the flashing details.
Apron at the front wall, step flashing up the side wall (both over the felt below, felt laps over above). I try to keep the siding 1/4" or so up off the flashing.
I'm not quite sure I get the fascia intersection to the existing roof. Are you talking about boxing the soffit like the pic in McDesign's reply? Thta's the existing detail of the soffits currently on the house, so I'll be matching that.
It seems like at the dormer roof-existing roof intersection I would run the felt paper from the existing roof to the new roof, put my rake fascia over the felt paper running along the new dormer rake fascia, but I'm not sure what the best flashing is to use at that fascia to existing roof intersection.
Should I keep the fascia off the roof by 1/4" or so and stick a piece of step flashing up behind it? That seems like it would keep water off of the barge rafter behind it.I hope that makes sense what I'm trying to get at there.
thanks
Yeah step behind the fascia between it and barge. I was proposeing closing off the really tight area where the dormer soffit dies into the main roof, just a verticle block the same width (height) as the fascia. You can hardly get in there to do anything, paint, flash, caulk, nail shingle..etc. Just a place for critters.Spheramid Enterprises Architectural Woodworks
"If you want something you've never had, do something you've never done"
Ok, I dig what you're saying. That makes sense with the vertical block, just closing off that little Bermuda triangle as it were. That makes sense in terms of keeping it easy to paint, roof, flash that area.Paul
There ya go. Make it dead space that never needs attn.Spheramid Enterprises Architectural Woodworks
"If you want something you've never had, do something you've never done"
OK, It looks like you have plans for th e framing but are asking about the shingle/flashing details.We leave the fascia there a god inch or so above the sheathing and do not nail it tight at that end. Then the roofer can slip the step flashing in as he shingles. You are saying 1/4" but you couldn't even fit a shingle there that tight. All trim materials and siding should be an inch above the finished roof surface so it does not wick up water and fail prematurely. So the best way to gauge that is to tack a 2x4 to the roof surface, then cut siding and trim to fit snug to it. After shingling, the siding is about an inch high that way.
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Yeah, everything's planned out, permits in hand. But I've seen enough water damaged dormers that I wanted to make sure I didn't go ahead and build another one that would fail at some point and have someone else come along and have to fix it. That's why I wanted to double check on flashing details for those intersections.An 1" seems right for water wicking prevention. You're right that 1/4" is small, it's the size of a nice drop of water anyway...it's like giving it a little ladder to climb up behind the wood!
This part - here I had a flat roof, but your sloped shed will be a lot tighter in there. Even this at ~40º was a booger to paint and flash. (And the roofers here will still complain!)
View Image
Forrest - not a roofer
Edited 8/31/2007 8:08 am by McDesign
The shingles should be taken back 3-5 feet. Leave them close and the framers will ruin them anyways.
As far as where to tie in - you need to do yourself a section drawing to scale. Gotta do that to know what length rafter materials to order anyhow.
This is reminding me of my BIL. he stopped in at my job the other day 'cause he is building a house. Asked if we could give him some time to help frame up the roof in a week or so.
I said sure, I'll come by to look it over on the way home...
So I get there. Job looks nice so far - even a little overbuilt, but very neat and clean
I ask where the plans are
NADA
24x24 cape with dustpan shed dormer 10/12 and 5/12 on knee walls but no plan of any kind.
I said be glad to help, but I gotta do a drawing and some calculations first.
I just don't know how anybody can work that way with no planning.
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