How to attach roof rake and ladder over thick exterior insulation?
I’m stuck on the details for attaching a rake/ladder to the roof through thick exterior insulation. Please see attached image for detail.
Roof:
– rafters/purlins
– 1×6 T&G board sheathing
– air barrier
– 10″ rigid insulation
– 2×4 vertical strapping (1.5″ vented air space) on flat side (not on edge)
– 1×4 horizontal strapping
– metal roofing
Wall:
– timberframe posts
– 2×4 framing
– sheathing
– air barrier
– 6″ rigid insulation
– 1×4 strapping vertical (3/4″ rainscreen)
– cladding
I’m in Northern Maine climate zone 7. We see much snow! The roof is 12/12 pitch.
This is the nearest similar thread I can find, though the OP did not work this detail thoroughly before starting the project.
https://www.greenbuildingadvisor.com/question/how-to-build-a-gabled-roof-on-a-rigid-insulation-roof
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Replies
The way I've done it is extend the ridge beam and the wall top plates out past the wall through the rigid foam and put a rafter between the two. This way you don't need any ladder framing. I had plywood roof deck to tie it together, would be good to also tie it into the 2x4 vent channels with the 1x4s.
Akos, interesting solution. I'll talk to the framer if its possible to extend the ridge beam in a high posted cape timber frame. This would make the fascia very thick, in the neighborhood of 13 to 14 inches.
Alan,
"This would make the fascia very thick " You can taper the ridge beam down from the exterior wall to the end of the overhang making the fascia any depth you want.
Rather than extend the framing at the bottom, I prefer to run a 2"x8" as exterior trim, and extend it out. I've attached an illustration of this on a shed.
Another option is to do what they did on Craftsman style houses and use brackets. In your case that would necessitate backing behind - as would my suggestion of using the exterior trim.
If you want thinner facia, one option is to build up the beams to the thickness of the foam than hang the rafter off it. This would let you get to a more standard 5.5" size.
The other option is to lag a fake ridge to the top of the roof, bring it in 3' to 6' to support the overhang(depends on the snow load on your area). You could do something similar at the wall top plates. If you make these the same thickness as your first layer of foam you can then cover it with the 2nd layer of foam. If you want even smaller, put it over the 1st layer of foam but now you are running into very long fasteners.
This option would make the air sealing easier as you don't have anything poking through the air barrier.
You call it a ladder but the drawing has an outside rafter but not one against the insulation.
Add one against the insulation with blocking every two feet or less. Build every thing tight and it wont move a bit.
This will work with up to about 12 inches of overhang.
Mike, the drawing I included is incomplete since I'm not sure how to handle attaching the rake to the gable end of the house. Yes, I would like to add a rafter and blocking against the insulation, but the problem is how to securely attach the rafter and blocking since there is nothing structural behind or below.
Alan, attach the the rafter to your strapping and use 2*12 flat if you worry that a 2*4 is not enuff.
I initially assumed a rake built out of flat 2x4s would not be strong enough. However, I spoke with a couple builders in my area and they suggested assembling the rake out 2x4s on the flat and securing with long screws through the foam into the timbers--same way the 2x4 vertical strapping will be fastened. In addition, the builders suggested I replace horizontal 1x4 strapping with plywood sheathing to give the rake strength. With only an approximate 8" overhang, I've been told this method will be more than adequate for our climate.
This method solves all my problems for assembling and fastening the rake. But I'm still doubtful about using 2x4s on the flat for an overhang--am I wrong?
Attached 3D model with revised rake design.
Alan,
- The overhang is fine. If it's more than a 2' cantilever change the 2"x4" strapping to 16"0c.
The way you have drawn it you have two problems: The floating double 2"x4"s, and the long unsupported overhang at the eaves below where the strapping changes direction to be horizontal.
- Start the change in direction 2' in, not 4'. That's how it's done on trusses, as long as there is sheathing above.
- Omit the double 2"x4" and replace it with a dropped 2"x4" on the flat. Move this 2" x4" in until it is over the exterior wall framing.
Malcolm,
"Start the change in direction 2' in, not 4'. That's how it's done on trusses, as long as there is sheathing above."
Followed your suggestion and updated the model to 2' wide rake, but wouldn't a wider rake be better in this situation?
"Omit the double 2"x4" and replace it with a dropped 2"x4" on the flat. Move this 2"x4" in until it is over the exterior wall framing"
If I understand, you're referring to the ripped double 2x4s under the rake. Those are intended to hold the soffit inside edge, and are fastened to the underside of the rake. Moving the "2"x4" in until it is over the exterior wall framing" isn't possible because the rake lays flat on the rigid insulation.
"Followed your suggestion and updated the model to 2' wide rake, but wouldn't a wider rake be better in this situation?"
The further you go back with horizontal strapping to support the overhang at the rake, the more vertical strapping you have to omit, leaving the corner unsupported at the eaves. (Or am I missing something? Are you supporting the eaves with the T&G below? If so then yes go back 4').
I understand the doubled 2"x4's now. Your detail should work as long as the foam doesn't compress. Having looked at this I begin to understand why houses using the "perfect wall" tend to omit overhangs: https://architizer.com/projects/perfect-wall-house/
I've only done this the normal way, with 2x4s on edge.
Your overhang doesn't sound like much but you have a lot of insulation plus siding, so you are getting close to 14" to 16". I would try to get some structural support to that double 2x4 from either the wall or the roof deck so it is not just hanging in the air there from the 2x4s on flat.
Even tying it in to the rain screen strapping on the wall would be better.
Akos, I assume you're referring to the ripped double 2x4s under the rake. The double 2x4s are fastened to underside of the rake and will support inside edge of soffit. (see model in my reply to Malcom--post #11.)
Yes, I can also fasten the double 2x4s to the wall strapping as suggested.
You could also box it out so that the ledger (the doubled ripped 2x4's being referred to) are in compression against the foam (and distributing the load). TO cover the shear force on it, could place the rainscreen strapping tight underneath it to support?
Might be overkill, but something like: