Question by BABAbooey: what is better to put under vinyl siding?
Is fanfold insulation or foam (rigid) insulation better to put under the vinyl siding?
Answer by T
Remove the existing siding first. As long as the sheathing under the old siding is rigid your best option is going to be rigid foam. Rigid foam comes with tongue and groove edging and will make for a much more consistent and even wall. Vinyl siding is very pliable therefore will flex and take the same form as the sheathing underneath.
After you install the rigid foam seal all the joints with a waterproof tape. This would be around all windows, splices, corners, cut outs around pipes or vents, etc. Make sure anything protruding from the house is caulked and/or sealed before you install the vinyl siding. Vinyl siding, being a petroleum product, expands and contracts in extreme temperature differences therefore must be installed loosely to allow for the expansion and contraction. That is why your rigid foam sheathing must be sealed completely before you install the siding.
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