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Old 01-19-2010, 01:59 PM   #1
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adding skylights to vaulted ceiling


Our main room is 25’x10’. The first 5’ of the house turns out to be vaulted. Now I do not want to, and cannot make the rest of the room vaulted – simply because there is another story above that section. It’s that first 5’ where it is just roof above. The type of roof we are talking about here is ‘hipped’ and the rafters are 2x6’s. There are no joists to this roof, it is vaulted.
A ‘paint’ drawing should help, sorry I do not know CAD and I do not have pictures – I can throw some together tonight if you’d like later tonight.
http://dl.dropbox.com/u/1491001/drawing.JPG

Ideally, we want two skylights. However, the rafters on this roof are unevenly spread apart, the widest two openings are 15 ½” and 15”. In fact, this won't even allow me to install a single skylight, I would need to cut rafters...

What I had in mind was to install new 2x6’s spread out to the exact width of the skylights, so the skylights can be supported by the new 2x6’s but also support the roof (and obviously add headers/footers for the skylights). Then, once these new 2x6’s are in place, remove the unevenly spaced rafters that would be in the way of the skylights. For strength, I was thinking of doubling the 2x6s on each side of the skylights.

By doing the above, I would not be changing, well, the look of the roof, and I would argue I would not really be changing the structure of the roof either. I'm no contractor though, so please tell me if this is the wrong way to look at things. Also, in this way, there would be no cutting of rafters in order to install the skylights.
Items I am assuming are: 1) the walls built by the original builder of this expanded section of the house are sound and 2) There is a header on the walls where the new 2x6's will be placed so I can place the 2x6's where I require - if not I would place where the wall studs are.
I should also mention that the the front of the house (where the 'front' of the hip roof is) is a large window; i'm not sure if this complicates things by adding more stress to this wall when adding skylights...

One last thing, the rafters are tied into the second story exterior of the house where the original wall was located on the first floor. This side is not load-bearing to the second story but it is now load-bearing for this small roof section.

Does this sound reasonable? Are you alarmed and if so why? What should I be carful of / look out for?

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Last edited by capslock; 01-19-2010 at 02:02 PM.
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Old 01-19-2010, 04:57 PM   #2
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adding skylights to vaulted ceiling


They sell skylights that will fit into a 14 1/2" rafter bay.
If you want a larger unit, you will need to double up all rafters around each skylight. That would mean running rafters from the main house to over the end wall where the window is. The window shouldn't be an issue .
Ron

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Old 01-19-2010, 06:30 PM   #3
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adding skylights to vaulted ceiling


Hi Ron,

Ok so I believe I know what you are talking about. Let's just confirm.


Here are photos of the rafters:
http://dl.dropbox.com/u/1491001/full.jpg
http://dl.dropbox.com/u/1491001/before.jpg

And here is a photo as to what I imagine would go down for the rafters. Each red line implies a 2x6 rafter. I am assuming in this photo that the skylights will be too wide for the space between the current rafters:

http://dl.dropbox.com/u/1491001/after.JPG


if we can find the skylights to fit that size then we will take that route.
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Old 01-19-2010, 07:05 PM   #4
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adding skylights to vaulted ceiling


Several concerns
The wall that the rafters lands on hopefully has a very big beam in there to hold the weight
Spanning 25' you would probably need (3) 12" LVL's to hold up the wall & floor above, plus the combined roof loads

By reducing the number of rafters & adding skylights you are putting more weight on the "corner" rafters for the hip roof

What size skylights are you installing ?
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Old 01-19-2010, 07:31 PM   #5
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Quote:
Several concerns
The wall that the rafters lands on hopefully has a very big beam in there to hold the weight
1 2x4 spanning the 10'. First, it's not load bearing for the main roof, however we are going to try to resolve this by adding two more and also raising said beam (it's "laying" below the new ceiling level.)

Quote:
Spanning 25' you would probably need (3) 12" LVL's to hold up the wall & floor above, plus the combined roof loads
Ahh, yes i agree. I'm not sure how one adds to this though if trying to add "up" instead of "down" i.e. up away from the ceiling instead of down. Also, the roof in question spans 10'. The roof we are speaking about is 5' by 10' plus whatever extra for roof angle.

Quote:
By reducing the number of rafters & adding skylights you are putting more weight on the "corner" rafters for the hip roof
I'm under the impression that the corner rafters would be the strongest rafters of the roof, I suppose my impression is wrong?

Quote:
What size skylights are you installing ?
22' 1/2" by 27' 1/2"
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Old 01-19-2010, 07:37 PM   #6
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adding skylights to vaulted ceiling


OK, not huge skylights so not a lot of weight
I almost always double the rafters on either side of a skylight
The only time I didn't is when I oversized the rafters from 2x6 to 2x12

The corner rafters take the most weight
In your pics one corner rafters has 3 rafters from each roof angle landing on them
I have no idea how to calc the load on a rafter like that
When I built my sunroom & additon I had a local lumber yard do the calcs for the LVL's I needed
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Old 01-19-2010, 08:15 PM   #7
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right, not huge so lighter than most. It will have the argon but it will be fixed glass, so no extra contraptions. Still, said windows will cover a good chunk on the roof.

Well, i agree, double the rafters on each side of the windows, footer/headers.


interesting point about the corner rafters. The corner rafters would be where the rafters holding up the windows would tie into. That's a bit concerning now, but the other side of each window would be supported by rafters tied into the house.
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Old 01-19-2010, 08:19 PM   #8
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adding skylights to vaulted ceiling


your red-line photo looks correct.
use double joist hangers for the opening bulkheads. don't trust nails to hold them.
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Old 01-19-2010, 08:55 PM   #9
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good idea about the joist hangers. I have never not used hangers, but what about the fact that the rafters will be at an angle tied into the corner rafters? I suspect that unless you can get a double hanger that can be bent at an angle, then i would not be able to use them
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Old 01-19-2010, 09:02 PM   #10
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A few concerns. 1. Rafters should have full bearing on their heel (inside), bottom of page, figure #4: http://www.housingzone.com/proremode...CA462902.html# Look at yours in the pictures, the level cut is not supported on the wall for 4" or so. This weakens the rafter size as to what it is rated for. Because it was framed this way, you cannot use the load tables for a 2x6 rafter. It may be stronger than a 2x4 rafter, but without a Structural Engineer figuring it, I don’t know by how much (if at all), and can only give you limited information.

Presuming rafters are Doug/fir, with fb of 1150#, graded #2, the hip jack rafters would be fine, even the commons (between the hips). BUT, the hips themselves (that carry all the ones tied to them) may be under-sized.

The hips carry 5’ of roof each side of them, by 5’ from the wall to ridge, = 5x5=25.
25 x 30# = 750# no snow load.

Hips, measured diagonally for a 5’ span = 7’2” 2x6 span- 7’ will carry 828# load

2x4 span- 7’ will carry 335# load The question is: are the hips rated at only a 2x4 because they are severely level cut, or how much more? I doubt they are rated at 2x6. And that without any snow load. You would gain back some of the additional 41# for the skylight and flashing (If Velux from H.D.) because some of it is bearing on the commons.
The wall should have been lower, or the rafters sitting taller on the existing wall to get the required seat heel bearing normally required. Doubling the sides would put more weight on the hips. Replacing the hip with an engineered member may work, depends on the level (weakening) cut again. I don’t know. I would get professional advice/liability.

Be safe, Gary
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Old 01-19-2010, 09:08 PM   #11
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good catch gary. I failed to notice that. the inward position of the heel would affect the behavior of the jack rafters.
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Old 01-19-2010, 09:22 PM   #12
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Looking at the framing pattern of the hip rafters, it looks as if it's not framed as it should be. The side opposite the future skylight osition has the rafters too far apart. While you're framing, I would fill in any over wide gaps.
As to the skylight being that close to the hip ridge, I don't know I'd put it there without some engineering guidance. It feels as though that the hip ridge would be doubled up as well as the rest of the perimeter framing.
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Old 01-19-2010, 09:53 PM   #13
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thank you all so far, this is great information.

So this is a drawing of how the rafters are in speaking of what GBR said, as you can see, there is a little lip there.

http://dl.dropbox.com/u/1491001/stud_rafter.JPG

as you can see, the rafters are actually not laying on the wall at all, they are hanging over. I believe some other parts of the house is like this as well as per it's style...

would doubling up the hip rafter increase it;s strength or would this not work?

Ron, good idea about the skylights just not relying on the hip rafter and instead staying more to the center. Ideally we would prefer two skylights over one, and in fact in order to have a single skylight in the center would mean a very small skylight in order to stay away from relying on the hib rafter...
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Old 01-19-2010, 09:57 PM   #14
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adding skylights to vaulted ceiling


I assume you are reshingling the roof as part of this ?
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Old 01-19-2010, 10:20 PM   #15
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actually no, original intention was to just remodel our main room, remove the false ceiling and raise. then we found that this area we've been talking about was vaulted so then we said let's add skylights. we are pretty much at the end of our budget at this point with all of the other side projects that were added to this...

re-shingling sounds like a better idea in the long run so we could just set everything the way it should be i guess? terribly larger project for right now and i was hoping to no redo our roof for another year or two...

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