Re-Siding a House With No Sheathing
Seattle – 4C
Hello All,
Re-siding and replacing almost all the windows on a house, save the entry porch that was redone by a different contractor recently. My problem is that the house doesn’t currently have any sheathing, except for in the entry way where there is OSB w/ tyvek (quality of install unknown). Currently the assembly is in the walls is = GWB – 2×4 framing – old old lap siding – with shingles over the lap siding. We are replacing the siding with some type of lap siding, but don’t exactly know where to begin as to if we should sheath the house or not? Seem like we have a great opportunity to make some major improvements, but also worry about creating the continuity, at least in the air barrirr, that is key for it working well. We’d like the improve the thermal comfort and overall durability of this house, but not risk trapping any moisture while maintaining a certain budget (I know, I want it all haha). Seeing as this house has little to no envelope currently, what is a good way to go about improving this? Would zip on the exterior walls (caulk/sealed to the exterior of the top plate) and then re-doing the upper level ceiling drywall (caulk/sealed to the interior of the top plate) be a good air barrier? Roof is a newer standing seam metal with some amount of rigid foam underneath (actual assembly currently unknown). Thanks for any advice you all may have!
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Replies
I am sure pros will weigh in with specific ideas for you but be sure to read these articles too (upgrades to houses without sheathing is a topic that comes up regularly on GBA): Insulating Walls in an Old House With No Sheathing, Insulating Walls Without Sheathing, and Managing Water and Insulating Walls Without Sheathing.
I would check that there is something for racking resistance. This doesn't have to be structural sheathough though -- you could have let-in diagonal 1x4 braces, or diagonal steel braces installed in notches in a similar way. If you have/had T1-11 siding, that siding WAS the structural sheathing and you should NOT remove it ALL at once.
If this were my house, I'd probably add structural sheathing just to lock things together, but it isn't always necassary, even though it does make for a much stronger house. I would at least put a 4x8 panel on each side of each outside corner of the house at a minimum though (basically you're adding shear panels this way). Make sure any structural sheathing you add ties the top and bottom plates together with the studs. That's important -- you want the top and bottom plates tied in so that they can't lift and seperate.
This is a great time to add exterior rigid foam too. If you have let-in braces, you can just put foil faced polyiso up over the studs, sealing the perimeter with sealant (I like polyurethane caulk for this), which will give you a good air barrier after you also tape the seams between panels. Zip can be used, as can plywood or OSB, pretty much any air barrier can be used here.
I'm thinking your lap siding MIGHT have contributed to the structural integrity of the assembly. I would NOT remove it ALL at once for that reason. It may be worth having an engineer check that for you just to be safe, especially since if that siding WAS structural, you WILL need to put up some structural sheathing.
Bill