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Install Flashing Correctly to Keep Water Out of Your Home

Flashing protects the vulnerable seams in your home from water. Installing it correctly helps to ensure your home will be leak-free.

Roofing and siding will protect most of the walls of your home from water penetration, but certain junctions of your home need additional material to keep water out. Flashing covers the vulnerable seams on your house. These seams are generally found where there is a joint between dissimilar materials, movement between two aspects of the building, or both. Two common areas where flashing is needed are the chimney and around doors and windows. These tips will help you to install flashing correctly in those areas.

Chimney and masonry flashing.
Creating a weatherproof flashing joint against masonry can be challenging, but is essential to seal off areas around your chimney. When installing flashing on bricks, chisel out a slot in the mortar joists that is about a half-inch deep, then fold in the top edge of the flashing and fill the joints with fresh mortar. If you are dealing with stucco, as opposed to bricks, cut out a shallow groove with a circular saw fitted with a masonry-cutting blade. Then place the top edge of the flashing into the groove, and cement it in place. A less effective method is to secure the flashing against masonry with tar, adhesive or caulk. This will probably work for a few seasons, until the top edge of the flashing will pull away leaving water free to run behind it into the house.

Door and window flashing.
The sides of doors and windows can be sealed with caulking, but you will need flashing across the top since this area is most exposed to the weather. Many doors and windows come with a molded strip of vinyl flashing, but you can use metal as a replacement. When working with new construction or a remodeling project, you will have room to tack flashing to the wall and cover the upper edge with siding. When replacing old flashing, remove a course of siding, or pry out the bottom edge and slip at least an inch of the flashing underneath. If you remove a few shakes or clapboards, be sure to tack the flashing with roofing nails along the top edge of the flashing, where the heads will be concealed once the siding is refastened. The exposed section of flashing should extend across the top of the window or door trim, and then tuck around its front edge.

Most vinyl flashing will curve away from the building to cover the trim. Be sure you don't crimp the curved section when you fasten the siding. You can always trim the lower edge of the siding, which will allow it to be nailed tightly against the wall without putting any stress on the flashing.

Source: Mike McClintock, The Washington Post.