Tom Silva's System Adding a deck to a house in Lexington, Massachusetts, This Old House contractor Tom Silva pays particular attention to the beam that connects the deck to the house and carries all the supporting joists. "It's where 99 percent of mistakes are made," he says.
Because a beam pressed tight against a house can trap moisture and encourage rot, Tom creates a gap for air with spacers shaped to fit the recessed foundation of the house. He cuts the spacers from scraps of pressure-treated wood, nails them on and then drills two holes through each spacer and the beam, one hole near the top edge, another at the bottom.
Tom and his nephew Charlie Silva jockey the beam into position. Aiming through the top holes previously made, they drill into the house's wooden sill and screw in lag bolts. Through the lower holes, they install masonry anchor bolts into the concrete foundation.
For flashing, Tom uses an adhesive-backed flexible membrane made of polyethylene film and rubberized asphalt. Tom prefers it to metal flashing because its sticky nature makes a watertight seal around bolts that penetrate the surface. Since the material could degrade in ultraviolet light, however, he makes sure to cover it with siding and decking. To prevent rot, Tom constructs the entire deck frame from pressure-treated wood. This wood is usually loaded with arsenic and chromium as preservatives, but he works with a look-alike product treated with a safer preservative, A.C.Q. For the decking, Tom switches to cedar or redwood because he likes the look.
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