Lap the flashing in the proper sequence to ensure that the flashing conveys moisture away from the sheathing.

Fasten the nailing fins according to the manufacturer’s instructions. Fasteners should be installed tight, unless the manufacturer directs you to leave them proud (see Figure 2).

Don’t puncture the nailing fin with extra holes when installing housewrap, exterior trim, wire lath, or siding. In all cases, fasteners should be held back from the nailing fin.

Leave a ¼-inch gap between the siding and the window to allow for expansion. Otherwise, wood or fiber-cement siding may restrict window expansion, causing the window to deform; in the case of stucco, window expansion may cause cracking.

You may need to adjust the gap depending on the temperature at the time the siding is installed. In cold weather, for example, the window will be at its smallest dimension, so the gap between the window and the siding may need to be larger. The reverse is true during very hot weather.

Don’t use expanding foam to fill the gap between a vinyl window and the rough opening. Vinyl windows frames, being less rigid than wood or aluminum frames, are particularly susceptible to being deformed by expanding foam.

Repair and Maintenance Vinyl is a relatively soft material that scratches easily. Fortunately, shallow scratches can be rubbed out with light steel wool, fine emery cloth, or Soft Scrub cleaner (an abrasive cleaner available in grocery stores). Scratches can also be removed with acetone, a solvent — but be careful, because too much acetone can dissolve the vinyl. For deeper gouges, some manufacturers recommend a liquid vinyl product called Stelmax Gap Filler Before repairing a window, contact the manufacturer so as not to void the warranty.