Weathertight Windows To the Editor: Regarding the article "Working with Vinyl Windows" (1/00), all the vinyl and vinyl-clad windows installed in my projects are applied to resist severe weather conditions. Caulking is never used as a primary means of defense against air and water penetration, as it has a high failure rate. If a vinyl window can expand and contract up to 7/16 inch, how can caulking possibly remain weathertight? Vinyl windows can be installed tight to the weather without caulking if three steps are taken. Step one is to place a bitumen membrane flashing pan over the sill before window installation. Step two is to use a good quality sealing tape over the nail flange and onto the housewrap