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Old 07-24-2010, 04:53 PM   #1
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Gable dormer construction questions


Hello everyone,

I've just joined this forum, and I'm looking forward to learning more about construction from you guys.

My current project (or soon to be project) is a set of three gable dormers over our garages. I have a fair amount of questions, but I guess I'll begin with just the ones off the top of my head.

First, the area I'm working with is a fairly steep roof (probably a 15:12 pitch), and the garage area is pretty wide, about 40 feet. So the dormer size I'm planning to go with is either 4 or 4.5 feet wide, by about 7.5 feet tall (from the outside height). I've spoken to a professional carpenter friend, and he said to build the side walls out of 2x6's and make the rafters 2x10 (or the size of the existing rafters). Now the existing rafters are, I believe 2x12's. My question is, is my friend going overboard with the size of the rafters and wall studs? The reason I ask is most of the construction plans I see online call for 2x4 framing, with 2x6 or 2x8 rafters and ridge.

The second question I have is about recessing the dormer slightly. Now, most plans online or other projects I've seen are only dormer that go up straight from the roof. I'm looking for a bit more of a traditional look, where the dormers are set slightly back into the roof (as one sometimes finds on a Mansard roof). Is there any particular way of framing this? I know you have to install a lower header, to support the interrupted existing rafters (followed by the front wall, built down to the floor). Now, I could simply triple the lower header, but that would only provide 4.5 inches of recess, which once flashed and everthing might not even amount to much.

I know this is probably not commonly down, especially nowadays, but does anyone have any experience with recessing a dormer?

I'd appreciate any help whatsoever. Thanks in advance.

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Old 07-24-2010, 05:18 PM   #2
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Gable dormer construction questions


As this will significantly modify the roof, you should get plans drawn up from either an architect or a structural engineer who has done an onsight inspection.
Internet structural guidance is useless.
Ron

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Old 07-24-2010, 05:42 PM   #3
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Yeah, I understand that the internet's no real guide for structural integrity. My professional carpenter friend, who looked at the place (inside and out), is probably not overdoing it with the 2x6's.

Regarding and architect/structural engineer, the dormers are only going to be 4.5' wide (max), so with double or triple trimmer rafters, I don't think it should really be a problem. I'll reconfirm it with a professional carpenter anyway.

Any tips info on the recessing, though?

Joe
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Old 07-24-2010, 07:29 PM   #4
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Sorry, no experience with recessed dormers.
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Old 07-24-2010, 07:35 PM   #5
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Originally Posted by Joe1. View Post
Yeah, I understand that the internet's no real guide for structural integrity. My professional carpenter friend, who looked at the place (inside and out), is probably not overdoing it with the 2x6's.

Regarding and architect/structural engineer, the dormers are only going to be 4.5' wide (max), so with double or triple trimmer rafters, I don't think it should really be a problem. I'll reconfirm it with a professional carpenter anyway.

Any tips info on the recessing, though?

Joe
I frame these all the time. Not really sure what it is you want to know about the framing. You can set it back as far as you want according to the existing pitch,window, dormer height.
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Old 07-24-2010, 10:16 PM   #6
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I frame these all the time. Not really sure what it is you want to know about the framing. You can set it back as far as you want according to the existing pitch,window, dormer height.
Hi Joe,

Well, regarding the recess, I'm just curious about the common ways of framing the recess itself. First, to make sure I'm explaining myself correctly, take a look at this picture: http://www.ontarioarchitecture.com/dundascross2.gif

That's the effect I'm looking for (specifically the dormer in the middle, with the pedimented gable). My roof is not that steep, but that's the look I'd like.

So, say if I want an 8-10" recess, do you simply create a small platform behind the lower header (and before the face wall begins)? If so, what's the proper way of doing that? Do you make it simply like a mini floor, with, say, 2x6 joists, and a band around it, to nail the face wall too?

When doing a recess, is it in any way not as strong as joining the face wall behind the header?

Thanks for the help, guys, and I hope I'm not being too unclear. I haven't done all that much framing before.

Joe, about the size of the rafters again, and studs, when you do your dormers, what size lumber do you usually do. Given the info. I mentioned above (2x10 existing rafters, 40 foot garage span and 25 ft rake length, 15:12 pitch, and 4-4.5' wide dormers), does 2x6 studs and 2x10 rafters sound right to you?

Joe
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Old 07-25-2010, 04:27 PM   #7
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Originally Posted by Joe1. View Post
Hi Joe,

So, say if I want an 8-10" recess, do you simply create a small platform behind the lower header (and before the face wall begins)? If so, what's the proper way of doing that? Do you make it simply like a mini floor, with, say, 2x6 joists, and a band around it, to nail the face wall too?
Are the garage joists sized for a room? Will this be living space? Or, are these just dummy dormers for aesthetic reasons?

Quote:
When doing a recess, is it in any way not as strong as joining the face wall behind the header?
The header gets framed in plumb with the rafters using hangers. The outside dormer wall sits on top of the header. Sometimes if there will be living space the floor joists can handle the weight of the wall framed on top with no header.

Quote:
Joe, about the size of the rafters again, and studs, when you do your dormers, what size lumber do you usually do. Given the info. I mentioned above (2x10 existing rafters, 40 foot garage span and 25 ft rake length, 15:12 pitch, and 4-4.5' wide dormers), does 2x6 studs and 2x10 rafters sound right to you?
All plans I work from are drawn by Architects and approved by the town. I've framed a million dormers and 95% of them the walls are 2x4. The rafters are minimum 2x6's. When I frame a dormer that's used for living space with a cathedral ceiling we use 2x8 for the rafters for insulation reasons. I have framed dormer spec'd with 2x10' and 2x12's.

Are you planning on getting an Architect to draw the plans, or can you draw them yourself and give it to the town for approvals and permits?
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Old 07-25-2010, 04:54 PM   #8
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Hey Joe,

Thanks for the reply.

Yes, the joists are sized for a room; it's a room already. The ceiling is open to the top, but there are 2x10 collar ties every four feet or so (with the sheet rock going right around them up to the ridge. So the dormers are for aesthetics and function. We have skylights already, but they look terrible on our house, and I'm tired of cranking the windows open, haha.

Regarding the plans, the town has already approved a basic elevation (front and side) that I made up. So the permit is all in place, waiting to be picked up.

Now, back to the lower header. The way I was originally intending on doing it was to hang the lower header, then build the front wall directly behind it, onto the floor joists (which in the garage is bearing down in the middle of the room onto a steel I-beam). If I don't do any recess of the dormer, like the in the picture above, I guess I could just bear down onto the header. Either way could be fine, I suppose in this case, right?

But if I wanted to make a recess, then I'd have to build the face wall down to the floor joists. So what would be the framing method there? Would I make the lower header down farther on the roof, then build a sort of deck on to the header, with the joists cut to match the roof slope up front?

Joe
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Old 07-25-2010, 05:17 PM   #9
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Regarding the plans, the town has already approved a basic elevation (front and side) that I made up. So the permit is all in place, waiting to be picked up.
You can a building permit to structurally alter you roof with just elevation drawings?
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Old 07-25-2010, 05:24 PM   #10
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Now, back to the lower header. The way I was originally intending on doing it was to hang the lower header, then build the front wall directly behind it, onto the floor joists (which in the garage is bearing down in the middle of the room onto a steel I-beam). If I don't do any recess of the dormer, like the in the picture above, I guess I could just bear down onto the header. Either way could be fine, I suppose in this case, right?
If you don't do a recess, you just frame the front dormer wall on top of the front garage wall. You don't need any header.

Quote:
But if I wanted to make a recess, then I'd have to build the face wall down to the floor joists. So what would be the framing method there?
Depending how far back you put the front wall of the dormer and if the floor can handle the weight, you frame the wall on top of your decking and you don't need a header. You will cut the existing 15/12 pitch rafters back 1-1/2" plumb enough for a single 2x12 ledger that will get nailed plumb to the front dormer wall and the existing rafters will get nailed to that ledger.
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Old 07-25-2010, 05:44 PM   #11
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You can a building permit to structurally alter you roof with just elevation drawings?
My old house:
I drew a new roof line on paper, basically 1 dimension, no elevation
Showing exisiting L shape roof w/flat roof.....then over top the new roof line
They photocopied my rough drawing for the permit
I did submit better plans a few weeks later
But I was issued the permit to start work
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Old 07-25-2010, 08:00 PM   #12
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Yeah, I was a little suprised that that's all they needed to grant the permit, but I guess that was it. I have to say, it was a pretty nice rendering .

Anyway, Joe, the dormer will be built set back from the garage wall. Maybe I'm using the wrong terminology, but when I said recess, what I meant was a certain style that some dormers have. The design includes a small sill or ledge before the dormer actually begins. So the roof has a cut out. Perhaps they are more commonly called "inset dormers", as they seemed to be called here: http://www.realtor.org/rmoarchitectu...atures/dormers

That's what I meant about setting it back, sorry if I was unclear. I'm just wondering how they frame such a design. I'm not really looking to have them inset as much as in the above link, but only somewhat--to make the dormers a little more interesting, and also to imitate some of the older houses in my area.

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Old 07-26-2010, 03:56 PM   #13
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This may help you in sizing the dormers and trim relationship: http://www.cambridgema.gov/~cdd/cp/z...rmer_guide.pdf

Joe answered the recessing at the end of his post, read it again slowly.

Be safe, Gary
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Old 07-26-2010, 06:01 PM   #14
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Yeah, I was a little suprised that that's all they needed to grant the permit, but I guess that was it. I have to say, it was a pretty nice rendering .

Anyway, Joe, the dormer will be built set back from the garage wall. Maybe I'm using the wrong terminology, but when I said recess, what I meant was a certain style that some dormers have. The design includes a small sill or ledge before the dormer actually begins. So the roof has a cut out. Perhaps they are more commonly called "inset dormers", as they seemed to be called here: http://www.realtor.org/rmoarchitectu...atures/dormers

That's what I meant about setting it back, sorry if I was unclear. I'm just wondering how they frame such a design. I'm not really looking to have them inset as much as in the above link, but only somewhat--to make the dormers a little more interesting, and also to imitate some of the older houses in my area.

Joe
Joe,

I know what you mean now. I've done them many times also. You set your first header plumb where you want to start the inset. Now you set the dormer front wall back as far as you want. You then frame new rafters from the plumb header to the front dormer wall with a ledger. Frame this with at least a 4/12 pitch for shingles or you go lower and put a copper roof.

Does this make sense so far?
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Old 07-26-2010, 09:15 PM   #15
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Hey Joe and Gary,

Thanks for the information. Joe, I got it now, thanks a lot. It's just like making a little angled deck before face wall.

Now, since it's a finished room already, with the structural members I mentioned above, framing the front wall on the floor joists shouldn't be a problem, right? Besides, isn't most of the load carrying taking place on the trimmer rafters anyway?

Anyway, Joe, now that I have the recess/inset understood, I'm wondering, if I use 2x6 framing for the walls, and I'm bearing down on the trimmer rafters on the side walls, do these need to be trippled and spaced? With 2x4, you can just put a half inch ply spacer, but what should you do with 2x6's? Trippling seems like overkill, but having the 2x6 walls hanging over the trimmers that much seems strange.

Thanks again guys.

Joe

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