What’s actually on your walls
Siding is only the outer layer of a wall system. From the inside out, a typical Oakland County house has wall studs, a layer of sheathing (plywood, OSB or, on older homes, fiberboard or wood boards), a water-resistive barrier such as house wrap or felt, and then the siding. Around every window and door, flashing and J-channel trim direct water out and away. At the bottom, a starter strip locks the first course in place; at the corners, corner posts hide the panel ends.
Vinyl and aluminum siding aren’t waterproof on their own. They shed most rain, but some water always gets behind them, and the house wrap and flashing are what keep it out of the wall. That’s why a re-siding job that skips new wrap and window flashing can look great and still leak.
How siding fails
Loose and unlocked panels. Vinyl hangs loosely on its nails so it can expand and contract. If it was nailed too tight, it buckles in summer; too loose or with too few nails, it blows off. See siding repair.
Cracks and holes. Cold vinyl cracks on impact. Woodpeckers, mice and carpenter bees go after wood siding and the soft spots behind it.
Water behind the siding. Missing kick-out flashing where a roof meets a wall, failed window flashing and clogged gutters send water behind the panels, where it rots sheathing and sills.
Worn finish. Aluminum chalks, vinyl fades and wood paint peels. At some point, refinishing isn’t worth it.
Repair or replace?
A handful of damaged panels on siding that’s otherwise in good shape is a repair, if a match can be found. Replacement makes sense when siding is past 25 to 30 years, the color is badly faded or chalking, damage is spread around the house, there’s rot or water damage behind it, or you’re fighting drafts and high heating bills. The siding replacement guide walks through the decision.