By Lee McGinley. I've remodeled houses for more than 25 years and am still amazed at the amount of water damage caused by poor flashing details. You would think that today's new peel-and-stick membranes would eliminate water damage. Not so. Even the best products won't work if they're installed improperly.
According to Paul Fisette, a building products scientist at the University of Massachusetts, housewrap and felt each have value in reducing air infiltration and water penetration (for more information, see "Housewrap vs. Felt," THE JOURNAL OF LIGHT CONSTRUCTION, November 1998, or go to www.jlconline.com). But installed incorrectly, they lose their usefulness.
Margins of error
The major installation error is reverse lapping the housewrap, regardless of whether it is lapping itself or used in conjunction with the flanges on a window or exterior door or metal flashing. Here are some rules to keep in mind:
* Housewrap should lap the course below it by 2 inches.
Don't forget that housewrap tapes will work only as long as the adhesive sticks. In other words, the tapes are no substitute for proper flashing techniques.
Alternatives to flashing
Sometimes the best flashing detail is no flashing, particularly on decks and outdoor handrails. Many contractors nail a deck ledger to the house and install a metal cap flashing over the ledger. A better idea is to stand the ledger away from the house so that water drains between the ledger and the house. For years, I've cut 1-inch pieces of 3/4-inch round electrical conduit and used them as spacers between the ledger and the house. Half-inch lag bolts make the mechanical connection. Better yet are through-bolts if you have access to the rim joist from the basement. Similarly, with deck handrails, if you stand the last handrail post a few inches away from the house siding, you've eliminated the requisite flashing detail where the handrail post attaches directly to the house.
A handy product for keeping water out is self-sticking rubberized asphalt membrane. I particularly like Grace's Vycor narrow flashing roll. It's great for taping the flanges on those pesky half-round and full-circle windows.
"If it doesn't fit, caulk it." How often have you heard this on jobsites? But good flashing details should use a minimum of caulk. And stay away from silicone caulks. They don't adhere well to wood. I've been using Phenoseal, an adhesive caulk, for 15 years and have been very pleased with its performance.
-- Lee McGinley, CR, a Big50 remodeler, writes for THE JOURNAL OF LIGHT CONSTRUCTION. He lives in Addison, Vt.