Extending gable eave
On the west-facing side of our house (climate zone 4), we have a gable end roof with the rake flush with the siding. This summer we will be repairing water damage to the wall directly beneath this gable along with re-roofing and re-siding. Since we’ll have everything uncovered, we’re taking the opportunity to wrap the existing board sheathing with a peel-and-stick membrane (Grace Vycor EnV-S) and two layers of 1” reclaimed polyiso. We’re adding a ¾” rainscreen detail to the walls as well.
I would like to add some overhang to the rake at the same time, but had some questions on how best to accomplish this:
1. Should the rake extension be fastened directly against the sheathing, or should it be attached through the 2” layer of polyiso?
2. Most discussions I have seen on extending a rake suggest cutting back the existing roof sheathing for one or two rafter bays and cutting new sheathing to span the extension and the cutback. We have closed-cell foam applied to the underside of the existing sheathing (a conditioned attic) – is this still a good idea? Or should we treat it more like a chainsaw retrofit, and wrap the air barrier around the roof-wall connection, and then attach the extension?
3. The prevailing wind in our area is from the north east, and we do get gusts over 100mph. The gable in question has a peak about 5’ above the wall, and a width of about 12’, and is 25’ off the ground. I am planning on a 2×6 ladder frame for the extension. Will there be any tear-off concern if it projects 12”? Or 14”? (The rest of the roof is pyramidal hipped, with a 14” overhang).
Thanks for any advice you can offer!
-Nathan
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Replies
Hi Nathan -
Before going to your questions, just wondering why you have decided to go with a modified bitumen membrane as your WRB? no question it can be a solid water-resistive component but it is a Class I vapor retarder. Could be that given the very low vapor permeability of your rigid insulation layers, you have decided that you won't get any drying to the exterior anyway, but just checking to make sure. Given this configuration, you should spec exterior wall components from the membrane on in that are vapor open or Class III vapor retarders to get some drying potential to the interior in your wall assembly.
Your questions:
1. Should the rake extension be fastened directly against the sheathing, or should it be attached through the 2” layer of polyiso?
Your WRB should connect or overlap with your roof underlayment.
2. Most discussions I have seen on extending a rake suggest cutting back the existing roof sheathing for one or two rafter bays and cutting new sheathing to span the extension and the cutback. We have closed-cell foam applied to the underside of the existing sheathing (a conditioned attic) – is this still a good idea? Or should we treat it more like a chainsaw retrofit, and wrap the air barrier around the roof-wall connection, and then attach the extension?
To connect your wall and control layers I agree that installing them first and then doing a ladder overhang is best practice.
3. The prevailing wind in our area is from the north east, and we do get gusts over 100mph. The gable in question has a peak about 5’ above the wall, and a width of about 12’, and is 25’ off the ground. I am planning on a 2×6 ladder frame for the extension. Will there be any tear-off concern if it projects 12”? Or 14”? (The rest of the roof is pyramidal hipped, with a 14” overhang).
你的2 6的小伙子der frame will be beefy enough at 12 inches of extension but the key will also be in your fastener type and schedule. I can't give you a structural analysis on this that an engineer or architect can give but I have had good luck going to tech support with a company like FastenMaster for their evaluation/recommendations.
Peter
Peter,
Thanks for your detailed response - it sounds like my original plan is appropriate.
As to your question about the air barrier, unlike other Grace products, Vycor env-S is rated at 15 perms - it seems meant to be a competing product to Henry Blueskin and Solitex Adhero. We chose it because we wanted a self-adhered membrane, and it was the most cost-effective one available in our area.