How vinyl panels lock together and drain — butt-lock, nail hem, and weep holes

Panels hook together at the butt-lock and hang loose from the nail hem; weep holes drain water that gets behind them. Because it drains, vinyl's laps and channel joints are never caulked.

An edge-on section of two vinyl panels at their joint. The upper panel's butt-lock hooks over the return at the top of the lower panel, locking the two together, while the nail hem above is fastened loose so the panel still floats. Small weep holes at the bottom butt let any water that gets behind the siding drain back out. Vinyl is a drained rainscreen, not a sealed skin, which is why the overlapping laps and the corner and channel joints are never caulked. — Source: ASTM D3679 · VSI Installation Manual

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An edge-on section of two vinyl panels at their joint. The upper panel's butt-lock hooks over the return at the top of the lower panel, locking the two together, while the nail hem above is fastened loose so the panel still floats. Small weep holes at the bottom butt let any water that gets behind the siding drain back out. Vinyl is a drained rainscreen, not a sealed skin, which is why the overlapping laps and the corner and channel joints are never caulked.

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