There were some 500 postings mentioning dormers here over the last 5 years or so and I’ve just read many of them. You’d think that nearly every angle would’ve been covered by that much writing but STILL I’m wondering about a very basic consideration. I’ll start with my own related set-up, then ask the question:
My house is 25′ long end to end not counting the overhangs. On the front side it has a full-sized intersecting-gable running transverse to the main ridge-beam. This full gable runs all the way out over the full front porch. So … it looks like the following picture BUT with the difference being that that gable in front extends forward to the front of the arch over the front stairs. Here’s the pic: ((the price of $1,870, by the way, has risen some since this plan was drawn))
http://architecture.about.com/library/nbungalowplan-s-3049-vallonia.htm
The BACK side of the house .. the side not visible in the picture .. is unobstructed from end to end. (The INSIDE set-up is different from the floor-plan that they give .. I can’t seem to find one that reflects mine accurately.) As I’ve mentioned here (too many times) before, I’m working at getting two sideXside dormers on the back side of this house. They’ll each be about 10 1/2 to 11 feet wide, with outside walls at both end walls of the house, and separated by 4 feet or so in the center, and they run about 13 1/2 feet from back wall of house TOWARDS the central ridge. At that point there’s a wall that runs parallell to the ridge beam and supports the back rafters at that point as they decend at a 7/12 slope to the back first story plate. This wall — and a parallel one running along the front side of the house — supports the ceiling joists for two upstairs bedrooms and these joists also act as collar ties to the rafters. The upstairs bedroom ceilings have about 5 feet above them to the ridge … so .. from the second (half)floor to the ridge is about 13 feet.
So — I’m coming off of the back-side rafters at a point about 2 1/2 feet hgher than the support-wall to create my two dormers … one now, one later … and the span is a LONG one to come out over that 13 1/2 feet and also get the height that I need. If I angle up enough to get a 1 1/2 over 12 slope I have an 18 foot span. I have a plan to support it mid span from the end walls on my dormer (the ones that run perpendicular to the ridge … parallel to the rafters) with a cross-header so the actual span of the new rafters will end up being about 9 feet(twice) and, therefore, I will be able to get away with 2X6 rafters 16OC. According to the roofing materials table that I have roll-roofing is appropriate down to 1/12 with a 4″ to half-lap cover, so I would also be able to go with that easy means of covering.
Then, in my last go-around here, someone suggested considering a gable dormer instead, but the books that I can find relating to dormers seem to mention gable dormers as smaller ‘light-grabbers’ and shed dormers as the most appropriate for large ‘space-grabbers’. A gable dormer always seemed too complex to me before… I thought it might be ‘beyond’ me. But now that I take a real look at them, and particularly in this situation, they actually appear as though they may be MORE appropriate for the job. And what’s more, they really don’t seem any more complex, structurally, than a shed dormer… and .. actually .. possibly lighter!
So I’m wondering about advantages/disadvantages shed -vs- gable dormers. And in all of the postings here (that I’ve searched and read) I can’t find this specifically discussed. Is it only a matter of aesthetics? Of personal taste? If it is then I’d like to go with what is simpler construction-wise as I’m a relative novice and also this is a very hidden back-side of the house that we do NOT care about the aesthetics of… only that it be safe and sound.
And one last thing: If I go shed, is it ok to come off of the old rafters a few feet down from the ridge instead of coming off of the ridge? Or … what’s the advantage of coming off the ridge. From the reading I did here it sounded to me like coming off the ridge meant building up the ridge … bulking it up somehow. But my ridge-board is only a wimpy 1X6 and I DONT want to get into major surgery here.
So … which is easier … more direct .. more streamlined for a novice to approach. Which makes more sense in this fairly straightforward situation; gable? … or shed?
Thanks!
Terry
Replies
Shed dormer definitely easier to frame. Less room for insulation. Less attractive (not a factor to you, as you stated, but I find them ugly, and have never built one). Gable dormer has better water runoff, steeper pitch, probably trickier tie-in for the roofing.
terry.. here's your pic..
View Image
as to which style ? your choice... shed dormers often end up on the back because they are easier to build .... GENERALLY give more room..
but really it's a question of esthetics and budget.. and the skill level of the builder
i could see two gable dormers on the rear.. but NOT extending all the way to the main gable end walls.. something along the lines of ( if you leave 4' between them) then i would hold them 2' from the gable ends
or... one large shed dormer.. but again .. NOT all the way to the ends...budgets change.. skill levels change.. but ugly just goes on for ever..
if that is your bungalow.. it's very handsome.. don't screw it up
I'd suggest you build a Dutch dormer instead of two sheds or two gables. You can tie this in below the ridge, but you will need support at that point in the form of wall parallel to the ridge. An awful lot of bungalows of that style or similar were built post-war and were designed to be expanded by the addition of the Dutch dormer once the growing family needed the space on the unfinished second floor.
It might be easier just to frame the rear roof from scratch as asymmetrical to the front, with a 2:12 pitch. This way you'd have a sort of Salt-box affair.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Huck ... thanks for the reply.
Mike ... thanks for putting the picture up! (donno how to do that). I really appreciate your caution with regards to 'building ugly'. But we're in a very very unique situation. Our house is situated on what is becoming more and more of an arterial street between a large brick apt building and a small neighborhood store. The back of the house is TOTALLY invisible to all views. A large tree in back seals the deal on that. So we're after ROOM ... that's our #1 consideration. Ugly, from the OUTside .. truly doesn't matter to us. Also, quite oddly, we've been informed by realtors that our house would surely be razed to the ground by anyone who bought it because, though it is completely lovely inside and out -- oak floors, lots of wooden built-in book-cases, tiled fireplace, beautiful crown molding throughout, leaded glass, etc -- the value of the lot, being zoned commercial, is more to a buyer than the house. So, though the house may be lets say worth 450,000 if it were half a block back from the commercial into the residential zone, the fact that it sits where it does means that it would only fetch the value of the smallish commercial lot ... say 200,000. Totally bizarre and I'm not even sure that I believe it, but that's what we've been told. So ... we would like to use it now and then perhaps rent it ... the more SPACE the better... and damn the hidden-in-back looks.
Dinosaur ... where I live one can build a shed dormer under 14 ft wide with MINIMAL hassle by the authorities. Over that ... as in the full-span dormer that you suggest .. and MAJOR permitting hassles kick in. I just went through a SIX MONTH rough and tumble with downtown over another project I'll be starting when these dormers are done and am just not up to it again. Also ... two 11 footers will suit our needs just fine ... and conveniently step around the chimney that's there in the center.
SO! --- It really began to look to me like the fact that a gable dormer comes so simply off of a rafter with it's one new ridge line and is supported so easily by the new dormer walls and does NOT have to awkwardly span some incredibly long space that it would actually be EASIER to build than a shed. The tie-in to the old roof seems pretty simple to me. But it sounds like the professional word here is that SHED is the easier way to go in the long run. Is that so???
IF I go shed, my current (old) rafters run only 22 o.c. -- to 'tie-in' to them below the ridge line would I come across with a board that's horizontal to the rafters to support the beginnings of my new rafters? ((I know... it must sometimes be scary to be in on the thinking of amateurs!)). Or, is there a better/best way to tie into the old rafters if their spacing is wrong? (The old rafters will NOT be 'headered off' as they continue on down to 8 feet where they tie into ceiling joists and are supported by a wall ... as per my original post, above).
I believe that this is the last question I have (yeah .. right...) before going ahead. My walls are built and laying flat upstairs and ready to be flipped up and joined together after the tear-off.
Any further thoughts on shed -vs- gable much appreciated. I can still go either way. But it WILL be to the outside walls -- for the room -- and it WILL be two separate dormers. Thoughts on the tie ins to the old rafters any one?
Thanks again!
Terry
The old rafters will NOT be 'headered off' as they continue on down to 8 feet where they tie into ceiling joists and are supported by a wall ...
Ceiling joists are not spec'ed to support roof loads; only a ceiling. You will be overloading these by doing as you propose, especially as your idea would put heavy point loads on each ceiling joist somewhere along its unsupported span. If you do it this way, it won't be long before the ceiling cracks. Catastrophic collapse is not out of the question, depending on what kind of live loads Mother Nature decides to put on your roof. All you need is a foot or two of snow sitting on the roof followed by a nice heavy PNW downpour and you will be in big trouble....
You need to devise some sort of structural support to hold up the bottom ends of the rafters you are planning to cut off. This is the purpose of headers in the most usual way of framing a dormer. Depending on the span, the header might be doubled or even tripled 2x, and the rafters the header hangs off would need to be doubled at least.
If your floor plan permits you to erect a supporting stud wall directly under the point where your old rafters land on the ceilling joists, this could replace big headers and doubled up rafters on each side of each dormer. If not, you'll have to do it the traditional way, or put in a beam and support it on posts.
There are tables in every major building code that will give you all the information you need to determine the scantlings for your framing. If you don't feel comfortable designing this structure yourself with the help of these tables, hire an engineer to do it for you.
One comment on your problems with the city building department: it is possible they are hassling you because you are a DIYer. See if you can find a cooperative contractor who deals with those civil servants all the time and get him to front for you for a small fee as a 'project consultant' or some such title. Remember, often it's not what you know but who you know.
Yeah, I know...it ain't right. But that's the way it is sometimes. Fight it if you've got the time and energy; otherwise....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
If your floor plan permits you to erect a supporting stud wall directly under the point where your old rafters land on the ceilling joists, this could replace big headers and doubled up rafters on each side of each dormer.
Dino -- this is EXACTLY what I already have and WHY I'm not building a header. (It's SO difficult to communicate all of this accurately without pictures/images!!!) That's what I meant to communicate when i wrote what you copied:
"The old rafters will NOT be 'headered off' as they continue on down to 8 feet where they tie into ceiling joists and are supported by a wall ... "
To say again: the old rafters slope downward from the main ridge until they meet with second floor bedroom ceiling joists at about 5 ft. down from the ridge and 8 feet up from the second floor floor. There, where they meet with the joists (which also act as collar ties), they rest on a studwall that forms one wall of the bedroom. That's going to be the back (inside) wall of the dormer and it's serving, the way I see it, as a sort of 'header'. And I STILL .. unnecessarily I now think ... trimmed (doubled) the outside rafters! btw I'm building my dormer walls ON the second floor ... NOT on the outside rafters. And despite the feedback I'm gravitating towards going with gable dormers because I don't like that enormous 18 foot span, even though I was going to try to mid-support it ... and because the more I look at them the rmore the gable dormer looks to me like the 'thinking man's dormer' ... and .. if anything .. i'm a 'thinking man' .. (( WAYYY TOO MUCH!))
No one ever responded to my repeated question of HOW to tie in the new rafters to the old ones below the ridge. My old rafters (again) are 22OC and I was wondering if a cross-timber to support the new rafters, supported by the old ones, would do it. But I'm a little nervous about so much strain on the old rafters from the ridge to the support wall. But if I go gable it won't be a question.
The "no dormer over 14 feet wide without a full permit process" as opposed to just a 'stop by and look-see' process is local code. I know that what you say about 'who does the appealing' to the powers that be is as true as can be ... but in this case I've already spoken with downtown and with two different established builders and two architects. It's down in black n white .. no gettin around it.
Thanks for your thoughts on this!
Terry
Okay, I just sketched for myself what I think you're describing. So here goes:
You will be cutting the old rafters off flush with the top plate of the stud wall. You will tie in your new rafters there. These will need to have a bird's mouth cut on the top and on the bottom, where they will land on the rear face wall of the dormer.
On the top end, the new rafters sit on top of the top plate of the stud wall, and are toenailed down into it and also sideways into the old rafter. You will keep the same rafter spacing as you now have. Pull your scantlings from the table for 24" centers and you'll be okay.
The new rafters will also serve as the ceiling joists in the dormers, if I read you correctly. In that case, you will need to vent the new rafter bays. Nail 2x2 blocking along both inside corners of every rafter bay, and tack on a sheet of Ten-Test over them. You may then add whatever insulation you like; urethane foam would be good but probably too expensive for the small amount of area you'd be doing (unless you shoot the entire roof at the same time). Other possiblities are rigid foam boards (in which case you can skip the Ten Test and nail the foam boards directly onto the 2x2 blocking), wet-pack cellulose, or good old-fashioned Fibreglas covered with Reflectix bubble foil VB....
The vent chute must lead clear up into the attic above the existing ceiling for airflow. You will need to vent the soffits of each dormer too, to allow ingress air.
Important: Note that the sidewalls of your dormers will be an important part of the structure of the entire roof assembly, in that it is they and they alone that will prevent the main roof ridge from tending to slide back downwards towards the rear of the house. The few full length original rafters you will have left will need all the help they can get in keeping that ridge where it is. SO: Sheathe the dormer sidewalls with structural sheathing; plywood would be my choice. Minimum 3/8", better ½". This will turn these sidewalls into a shear panel and that will help keep your old roof where it belongs.
Let us know when you start figuring out how you're going to flash the dormers in and do the roofing....
You might be wise to get an engineer to go over your final framing plan before you cut a couple of big holes in your roof, just to make sure everything is on the up and up. I know how I'd frame it, but I'm here and can't see your building. So....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Edited 5/10/2005 7:33 pm ET by Dinosaur
Dino -
Thanks so much for your time and expertise ... I continue to marvel at the willingness of so many here to go out of their way to be vitally helpful to some total stranger!
The picture you've (verbally) drawn of my situation/plan is near perfect. However, there is one element, mentioned often by me and even pretty strongly 'featured' in my posts, which I have clearly failed to communicate. That is, that I was planning on joining to the old rafters that are extending down to the support-stud-wall NOT at the top of the top plate of the existing stud wall, but, rather, a few feet UP the old rafters so that the new rafters actually 'soar over' the stud wall at about 2 feet higher. This, to get some slope on the roof while maintaining the heighth of the new-dormer ceilings. It would then be the CEILING joists that would rest on the old stud-wall ... and on the new face wall.
Now - my original plan was to just come straight across to the new face-wall from the old stud wall and have a flat roof. I DO see them around here and there ... even here in rain-city. The top of that old stud-wall (existing) that I'll be relying on and making use of is, now that I've completed my new second story floor all across the back half of the house, 7' 9". So, I could actually afford to do it your way and come down on a VERY gradual slope to 7' or so at the front face-wall. But this would be only a 1/2 / 12 or so slope ... not even enough for roll roofing. (Just now it occurs to me that I could come up.. build up with 2/4's ... say 3 or 4 1/2 inches between the old rafters on the old stud-wall plate and thereby get a little more heighth at that end of the new rafters while still using the old stud wall for support. But to get enough heithth that way to drop to 7 feet at the outside face-wall and still get the minimum of 1/ 12 slope I'd have to build-up the heighth of the top-plate by approx 5 - 6 inches. Whaddaya think?) But my original question was, 'how do I come off the rafters UP FROM the old stud wall ... or ... should I make it easier and just go gable >> ONE long ridge rafter and many much shorter/steeper rafters coming down to the sidewalls. This is what I've been imagining of late. Hence my posting: 'which better - shed or gable'
Now, of course, I've got about 3 different possible approaches ... all nearly equally attractive ((Libra = 'balance'... bummer when it comes to decision-making)).
My side walls are largely built and lying there on the new floor .. awaiting erection. They'll definitely be sheathed in 1/2 cdx ... as will the whole back roof as so much of it is coming off that I'm just going to go ahead and re-do with sheathing over what's left of the old skip-jack.
I remain uncertain as to the best way to come off of the old rafters further up between the top of the old stud-wall and the old ridge ... if I do end up doing it that way for a new shed-dormer. Otherwise ... perhaps building up that old stud wall as mentioned above and sloping down to 7 feet at the new outside face-wall would be best. Otherwise, lastly, a gable dormer sounds better and better! Which would you do?
Thanks again for your time!
Terry
I can't see the geometry sufficiently well from your description to judge whether or not taking the new rafters off in the middle of the span of the old would be acceptable or not. You could get an engineer to calculate that for you; that would be the safest way.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Thanks, dino --
It's just a question of trying to work in some slope by coming off those rafters a little higher than the top of the exisiting wall. Your image of it seems spot-on to me. But I hear your suggestion of an engineer's eye.
Terry
More his slide rule than his eye....
Good luck. Let us know how it turns out.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.