Siding is not waterproof and was never meant to be. Wind drives rain up behind lap joints and around every penetration, so a certain amount of water always gets past the panels. The system is designed around that: the layer behind the siding is what actually keeps the wall dry, and its job is to catch that water and send it back out.
That means housewrap lapped shingle-style from the bottom up, taped at the seams, with flashing over every window head and door head that laps over the wrap below it. Around windows it should tie into the sill pan. It is unglamorous work and it is entirely hidden once the panels go on, which is precisely why it is the first thing skipped on a cheap quote.
The other thing worth knowing is that vinyl siding is meant to hang, not to be pinned. Nails go in the centre of the slot and stop about a sixteenth of an inch short, so each panel can slide as it expands and contracts. Panels nailed tight buckle in summer heat into the wavy look you see on badly done elevations — and once they are locked, thermal movement has to go somewhere, which is usually a split at a nail hole.
Planning a re-side, or chasing a stain on an interior wall that keeps coming back? Call Empire AH Home Improvement at (551) 219-7785.
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