Ledger board for porch roof with exterior insulation
I’ve been looking for answers on this forum and have come across a few solutions but not really any that fit my exact situation. We are planning to have a porch off of our house. I was hoping to attach the ledger board for the porch roof to the house, into the 2nd floor studs, not the rim board because the porch roof would end up too low.
We have two layers of 1.5in polyiso to make up 3in of exterior insulation in the house. Originally I was thinking I would remove one layer of the insulation and attach a 2×6 ledger board which would be flush with the outer layer of foam, but it seems like attaching the ledger through 1.5in of foam is probably not a great idea. I would like to reduce thermal bridging so I don’t really want to cut the foam all the way back to the sheathing for the ledger.
I was looking at the Maine deck brackets but it seems like those are for use in a rim board? I guess I could add blocking to the wall on the interior if I went with those but then the weight of porch roof would be on the sheathing, would that be a problem?
We are still figuring out how we’ll anchor the supporting posts, too. Either thinking of pouring sonotubes or using some kind of ground anchors but need something that can stand up to the frequent strong winds.
Any advice on what to do here would be greatly appreciated!
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Replies
Maine deck brackets must be through-bolted into a rim joist. Ideally, that rim joist is an LVL.
Given that you don't have framing in place to support a roof ledger or connectors in other ways, seems to me that you'll have to cut through the foam to allow direct connections into studs and not worry about the the small amount of bridging you've created at each rafter as you can apply foam over the ledger and between the rafters once they're in place.
Otherwise, possible that you open the wall from the outside and notch an LVL into the studs. You'd have to open the wall from the inside, too, to bolt the brackets to the house. Also, you'd need to consult an engineer as MDB are designed for deck loads, not roof loads.
I'm sure others will have good input.
CC,
I like your suggestion of letting in the header into the studs. Solves a lot of problems at once.
The roof and deck loading should be petty similar shouldn't they?
You can probably use this but you need a rim joist on the inside to bolt against:
https://ssttoolbox.widen.net/view/pdf/zxvwnzzwbg/L-C-BVLZPRESC24.pdf?t.download=true&u=cjmyin
I think the simplest is to pull back all the foam and install the ledger straight to the sheathing then cut and cobble the foam back in between the rafters.
EDIT: Another option, instead of a ledger, install two beams on either side of the porch and run purlins across for the roof. The beams would still poke through the foam but much smaller cross section area.
Because the loading on Maine Deck Brackets is concentrated, typical in-wall blocking would not be sufficient to resist lateral forces. Do you have rafter ties or other means to resist lateral forces?
I design super-insulated homes and have dealt with this issue many times. For safety and simplicity, I just bolt the ledger directly to the sheathing with GRK RSS screws, or similar. Unless it's a Passive House, in which case the porch needs to be basically self-supporting.
Great, thank you all. I will mount the ledger to the sheathing and screw into the studs. I’ve been trying to find a detail for flashing a porch roof ledger with exterior foam and have only found deck ledger details. Because the ledger will be set back from the face of the foam, I’m wondering how the flashing should be done.
Cottagebuilder,
Unlike deck ledgers, roof ledgers don't get flashed. The roof framing is sheathed and it doesn't matter whether there is a ledger below, or how it is attached. End-wall flashing will cover the top of whatever roofing you use, and extend up the wall behind the WRB.
Could you have the porch as a separate structure with posts along the outer and inner lengths so you don't have to penetrate the exterior shell of your house?