After bending a short lip on the back of the vinyl coil stock, the author uses 49/16-inch gauge blocks.
After bending a short lip on the back of the vinyl coil stock, the author uses 49/16-inch gauge blocks.

I’ve heard it said that there are two types of windows: ones that leak and ones that will leak. That may sound a little harsh, but the fact is that leaks frequently occur at windows. The perimeter flashings are a good first line of defense, but if the window itself fails to keep water out — a fairly common occurrence — the framing and interior finishes can get wet. The surest way to avoid that problem is to install sill pans under all windows and exterior doors.

A sill pan is a three-sided pan installed across the bottom of the opening and integrated into the weather-resistive barrier (WRB). Any water that makes it through to the rough opening will be caught by the pan and drained to the surface of the WRB. While there is a cost to installing a sill pan, it’s a lot less than the price of a callback or a...

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