Inexpensive and effective, flashing makes your beach home watertight.

By Michael Haigley
September 02, 2002
Terry Pommett

If you're an avid reader of this column, you know I'm a fanaticabout preventing water from penetrating walls and floors. And ifyou want to live in a coastal climate, where wind-driven rain is aconstant, you'll probably develop the same obsession?especiallywhen you consider the costs of replacing rotted subflooring andjoists.

Flashing is a time-tested technique we use in Nantucket forbuilding extra protection into door and window openings. Besidesbeing effective, the process has two other giant advantages: It'ssimple and cheap.

I'll describe the technique for exterior doors. You can adaptthe steps for windows.

The problem. The most dangerous effects of water accumulationoccur where you can't see it happening?beneath layers of siding orflooring. If you're building inland, caulking may seal out mostmoisture. But on the coast, you need flashing.

The material. I've learned through trial and error that the bestflashing material is lead or lead-coated copper. Usually, I putabout 600 pounds of lead into flashing around windows and doors.Unlike copper, lead is soft and a little lumpy to the eye. Butit's easy to shape on the job site without special tools. Onceinstalled, it's concealed by trim or siding or molding. It costsless than $20 in materials, and it could save thousands in repairslater.

Creating the pan. For most doors, a 14-inch by about 4-footsheet does the trick. Place the lead sheeting, long side formingthe width of the door opening, directly on the subflooring. The4-foot length of flashing is enough to cover the threshold andbend up the sides of the studs. Its 14-inch width lets you extendit about 2 inches beyond the threshold on the interior and thesame on the exterior. Crimp up the edges of sheeting on the insideso that about 1 inch sticks up from the subflooring. When thethreshold is installed, this edge will be sandwiched between thethreshold and finished flooring. On the outside, bend the flashingdown the side of the wall. Bend it over the top of the felt so itforms a downward lip.

How it works. What we have now is a three-sided moisture traprunning beneath the threshold, up the sides of the rough doorframing, and against the flooring. The fourth side is the lip onthe exterior, dumping any water that accumulates beneath the doorback outside. It's a self-draining pan. If I need to secure it, Inail the top edges of the lead bent up the sides of the studs (notin the bottom) to prevent any leaks.

Final trims. On the interior side of the door, the finishedflooring is butted right to the upturned lead sheeting against thethreshold. The sheeting that sticks up over the flooring istrimmed flush with a sharp knife. I'll use a 3