Vinyl siding and its accessories are designed with elongated slots to accommodate movement as the product expands and contracts. It also is important to leave a gap between the nail head or staple and the siding nail hem to account for movement on the nail shank. About 1/32 inch—the thickness of a dime—is the recommended gap. Position nails in the center of the slot to allow for expansion.
A good tip for assessing proper nailing is to make sure you can move the vinyl siding side to side or a corner post up or down slightly. Visually, you also should see a gap between the end of the siding and the back of the accessory. On the flip side, it is also possible to leave too large a gap. Overlapping siding and accessories is important; if pieces are cut too short in the heat of summer, they could possibly shrink out of the pocket of the accessory in the winter. Overlap one panel over the other by half of the factory notch, or approximately 1 inch. If the overlap is not enough, the panels could separate in colder weather; if it is too much, movement could be restricted.
When overlapping siding, face the overlap away from the driveway or front entryway to avoid showing seams. Overlaps or joints should be randomly placed, and if one joint needs to be directly placed above another, there should be a least three rows between them. To avoid waviness, look down the length of the panel when installing and adjust the nail in or out to keep the top lock straight. If the nail has to be adjusted out more than 1/4 inch, a shim should be placed between the wall and the back of the panel.
As you install panels, always check that the buttlock, or the lip at the bottom of the panel, is fully engaged with the panel below it for the entire length of the panel. When you get to openings or the top of a wall, there are techniques for installing partial profiles. Consult the Washington, D.C.-based Vinyl Siding Institute’s Vinyl Siding Installation Manual or your manufacturer’s instructions for details about these specific installation procedures, as well as proper techniques for installing fascia and soffit on a home.