A roof framing question related to deck mounted skylights
I’m in the process for framing in some skylight rough openings before we re-roof. (It’s an old house; the roof job will be a complete tear-off with plywood sheathing nailed over the existing skip sheating) When in the attic and measuring for the new rafters, I noticed a detail that I wasn’t expecting. The common rafters end at the outside of the top plate and the overhang (2′) is created by shorter rafters face-nailed to the common rafters; they extend in around 18″ or so. The weird thing is (the thing I wasn’t expecting), the slope of these shorter rafters that create the roof overhang are at a different slope than the common rafters. I can easily see this by putting a long straight edge along the top of the common rafters right underneath the skip sheathing. I actually expected the common rafters to be bowed but surprisingly enough they are quite straight (I checked in a few spots with straightedges and strings).
What’s the deal with this type of detail? Why would someone put in these rafter tails at a slightly different slope? The problem for the skylights is that I now have to position the skylights a bit further up from the exterior walls because they need to be on a straight surface; they are Velux deck mounted skylights. I would think that even with a nice clean neat surface of plywood sheathing, there would be a slight crease there two slopes meet. Since the skylights are deck-mounted and they assume a straight mounting surface, it would be problematic if the skylights were installed in the area with slight slope change. It is really slight, and not visually noticable, but the skylights are straight and there would be a gap. I’m assuming that this would be a problem
Has anyone had to deal with a detail such as this when installing deck-mounted skylights?
Thanks in advance for any advice!
Cheers,
jonR
Replies
I don't see what the problem is, unless you really wanted the skylight to be closer to the top plate. As to why it's made that way, it must have been a style issue back in the day, or it was done for clearance or daylight issues.
Heh, yes you do see the problem. This is forcing me to move the skylight higher up on the roof and farther from the top plate/exterior wall. I wanted to place it at a particular location because of how I wanted the well to look on the inside. However, I can work around it and redesign the well. In another location (kitchen), I have the same issue and it will force me to move the skylight further uphill and closer to the hip than I would like.
It only goes to show that you can create really accurate as-built plans, and use CAD to make it even more efficient, but that's not enough. I guess you need to crawl around in the attic in the rat s*** and spider webs and dust before you've done a complete job. That's the only way you can see a surprise detail that will force you to change your design. :-)
At this point I can't envision a solution that will allow me to place the skylights in the area where there will be a slight 'crease' in the sheathing and still have a straightforward install with no potentional leak problems later on.
Heh, yes you do see the problem. This is forcing me to move the skylight higher up on the roof and farther from the top plate/exterior wall. I wanted to place it at a particular location because of how I wanted the well to look on the inside. However, I can work around it and redesign the well. In another location (kitchen), I have the same issue and it will force me to move the skylight further uphill and closer to the hip than I would like.
It only goes to show that you can create really accurate as-built plans, and use CAD to make it even more efficient, but that's not enough. I guess you need to crawl around in the attic in the rat s*** and spider webs and dust before you've done a complete job. That's the only way you can see a surprise detail that will force you to change your design. :-)
At this point I can't envision a solution that will allow me to place the skylights in the area where there will be a slight 'crease' in the sheathing and still have a straightforward install with no potentional leak problems later on.
I think you could frame in a curb to set the skylights on, and have them where you want them to be. Of course there's that pesky flashing issue to deal with. Most skylights come with great flashing to mount them flush on the roof. Raising them up off the roof would be somewhat more challenging.
Hi Mark,
Thanks for the suggestion but building a curb is not an option. These are specifically deck-mounted skylights and I'm pretty sure a curb solution will not work and even if it did it will be asking for trouble. These Velux units have a wood frame underneath the cladding and have this flange/lip that does around the entire unit. The flange is there to nail directly to the roof sheathing. This flange detail I believe was introduced in 2010; prior to that you'd fasten these Velux deck mounted units with 4 metal brackets, one @ each corner.
I've already worked out a good solution to the bathroom skylight. It turns out moving it into the room a bit further will be fine. In fact I'm actually starting to like the new layout. The only thing I would have done differently is perhaps get a slightly smaller size skylight (in the height dimension), but I'm fine with what I purchased.
For the kitchen, that will be a bit more challenging because I can't get too close to the hip. If I decide I can't move the skylight up from the exterior wall, I may toy the idea of ripping/creating a wedge of some sort to take out the crease. I wouldn't do this unless my roofer OKs it. But it seems like something I could easily do on my table saw as a workaround. Since we're laying down new CDX plywood over the skip sheathing, I think there's some 'wiggle room' for improvisation.
thx,
jonR
You have a flared eaves roof. Architectural detail, looks good on some houses: Also used to keep soffits at a defined height to clear doors and windows. http://www.houzz.com/photos/query/flared-eave
Build a curb where you want it, and flash it with peel & stick. Mount the skylight to the top, and flash that to the curb with peel & stick. Add metal step flashing to the curb / roof the same way you do a chimney. Counter flash the skylight to the step flashiing, engaging the flashing slots in the skylight. You may need to get some flashing made up to match your skylight and curb details.
Not difficult, just attention to details.