Rafter tails on 14x24 Little house

[Bretzel.logic]

Just curious if anyone has done the sistered 2x4 rafter tails detailed in the Little House plans? Having never framed anything before, I'm working on a cardboard model made from pieces of double thick cardboard cut to scale as dimensional lumber. It's been fun and helped me see what things I may encounter.

One of them is that the rafter rails being offset makes them not on 24" oc for my roof sheathing.  Do you just have a separate line of sheathing (the width of the overhang) over the rafter tails thats properly nailed? Ideally, I would think you would want the rafters tied to the tails by the sheathing, so I'm not sure if that's the solution. 

Looks like most people just buy longer rafters and do the birdsmouth cut on them to extend. Leaning towards that right now.  Thanks in advance! This forum has been really helpful and will undoubtedly continue to be for our build. 

-Brett    

[NathanS]

I'm about 2 weeks late here and not sure what the sistered 2x4 rafter detail is. Assuming your rafters end at the top plate then you nail a 2x4 on to the side, something like 2 feet in for every foot out?

It probably ends up working fine but would be inferior to just cutting your rafters down to width after the birds mouth. It actually seems more like a detail for a repair than new construction.

You are right it would make the roof sheathing awkward, and while a strip wider than 16" does work for the roof diaphragm, it doesn't seem like a good to put a hinge at the overhang for snow load or uplift.

[Bretzel.logic]

After some more research on the topic, it looks like people usually put a weather resistant T & G plywood over the exposed eave. That's what it looks like in the "Graphic Guide to Frame Construction" on pages 144-145. The detail there shows the plywood meeting over the blocking between rafters. 

Page 164 also briefly explains this. Says solid T & G can also be used, although I'm not sure if you could find that in the same thickness as your other sheathing? 

[Bretzel.logic]

Even if you do an extended rafter (cutting bird's mouth instead of attaching a sistered "rafter tail") and you want to have an exposed eave, you would still have to use a treated sheathing on the exposed part. I would think this would be pretty solid as far as creating a hinge goes. You'd have a seam in your plywood all the way around at the start of the overhang, but nailed properly, seems better than the sistered 2x4 option.   

[NathanS]

Yeah, if you leave the rafter tails exposed, t&g would be a nice detail, and you're right to think about the transition to sheathing. In retrospect I would not worry about the 'hinge' as the real source of strength is the rafter.

I built my workshop last summer and I actually ran purlins over the rafters - for the rake overhang I just ran the purlins out. Really fast and enjoyable way to frame. For the interior gable section of the garage I had a felt membrane factory apply to the metal to prevent condensation.

[Bretzel.logic]

Thanks for sharing that photo.. I'd like to build a similar shop someday.  I've been considering extended porch roofs off the eave of a gable roof, as you have there (on both sides, it looks like) but have thought the snow loads in my area will be a problem.  Snow from the main roof would pile up at the transition from steep to less steep roof, and load up on the porch roof. I'm in NE Minnesota near Lake Superior.   

I see you are in NY mountains, where I assume snow loads are probably similar. Has this been an issue or something your worried about? Would love a covered porch on the longer side of the building, but if the snow is an issue I'm thinking doing a shed style roof with the porch on the higher side would also work.  On the higher wall, you could start the porch roof higher, it could be higher pitch so snow could shed off. 

Also I like the idea of purlins instead of sheathing but I'm curious whether a water barrier is possible (or necessary?) with them. 

[NathanS]

As long as your rafters sizes meet or exceed the prescriptive code tables I wouldn't worry about it. Exception is if you had a 2 story roof dropping snow onto a 1st story roof, then you would want to size up and be careful with connections. I am in 50lb snow load territory, but at elevation. I framed my house roof on 16 inch centers with 2x10s, and I'm pretty certain the rafter joist connection would fail before the rafters.

If you decided to go the purlin and exposed fastener metal roofing route, I used ABC roofing with "drip stop" applied to the interior roofing in my garage. Earlier this winter the exterior non-dripstop metal looked like someone sprayed it with a hose, and the drip stop I'm the attic was bone dry. It's not cheap but the installation was a dream. In snow areas you want to make sure metal roofing fasteners are sunk into a good connection like purlins. I noticed that snow will rip fasteners that are fastened to OSB.