Vinyl siding over rigid insulation
jklump
| Posted in GBA Pro Help on
I have a multi family project that needs to be resided. Unfortunately we cannot afford to use cement board siding and are using vinyl. Is it possible to attach vinyl directly over rigid anchoring to the sheathing? It doesn’t seem to be an acceptable attachment method from the vinyl siding manufacturers. Is it worth installing sheathing over the rigid, perhaps a taped zip system? Thanks.
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Where I live (northern Ontario), Virtually all re-siding projects for the past 15-20 years have included rigid foam. In my travels as an energy auditor and home inspector, I haven't seen any vinyl siding installations failing due to improper fastening through foam.
Julie,
The installation instructions of the Vinyl Siding Institute and most (if not all) vinyl siding manufacturers allow vinyl siding to be installed over rigid foam sheathing. The illustration below comes from the Vinyl Siding Institute.
The VSI installation manual notes, "When the fastener must penetrate through a non-nailable material such as foam sheathing, the thickness of that material does not count toward the total. In such cases, the fastener will need to be long enough to penetrate through the non-nailable material and then 1 1/4” (32mm) into wood framing or other nailable material."
.
Dear Julie: Here is another option that is often easier than trying to use long nails / screws with siding, particularly if you installed 2"+ thick foam board. Install 1x3" or 1x4" boards vertically along the walls, and around the windows / doors. We recently completed a project in Massachusetts and used this approach, after we wrapped the house with 2" XPS foam board. A couple of photos are attached.
A few related tips:
(1) Be sure to carefully seal all of the joints, edges and corners of the foam board to block air leaks. If cold air flows in behind your foam board, this would obviously defeat the purpose! The 'Windows and Doors' version of Great Stuff works well; the cured foam remains flexible to avoid cracks as things expand, contract and shift. We also applied a generous layer of DAP 230 over the joints, to make sure they were air-tight. This also blocks water infiltration behind the foam board.
(2) Did you make sure the foam board is thick enough to prevent condensation on the sheathing? In many areas of the USA, R10 is required -- which equals approximately 2" of most foam board products. Condensation and rot is a particular risk with OSB sheathing.
I hope this is helpful.
Mark
Thank you both, hopefully I can convince my builder to move in this direction. Mark, can you tell me what vinyl siding manufacturer you used? I think if I can get them to agree to the attachment method, we will be ok.