Hollow vinyl siding installed over fan fold insulation has an R value of 1.Most installers still using this out dated vinyl siding just nail fan fold insulation over old siding and install hollow vinyl siding.Installing solid core vinyl siding house must be stripped,house wrap installed.Some solid core vinyl siding has a R value of 5 and a perm value of 5.You really should look at both products to see if you think there is value in the solid core siding.IspectorD says I am misleading saying R value of 5,well solid core vinyl siding is Energy Star rated.Fan fold insulation is not rated Energy STAR.
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