Flashing helps direct the flow of water around openings. Since water
can seep into your home’s walls, deteriorating building materials, causing
structural damage, and creating moisture and mold problems, it's very
important to properly install flashing when constructing a new house or
altering the exterior of a house. Flashing is used beneath the first course
above ground level in a masonry building, above all wood trim on shelves,
doors, and windows, where exterior stairs and decks attach to the house, and around any features in the roof structure. Below are some of the common
flashing details on residential roofs.
Flashing can be made of sheet metal, plastic, or composite materials.
Sheet metal flashing is the most durable, and usually the most expensive
choice. Copper or stainless steel can be used as flashing. Plastic
flashing, usually PVC-based, is a less expensive alternative to metal,
but if parts are exposed, it can wear with direct sun contact.
Dormer: Metal flashing is usually chosen for dormer windows. Flashing
squares are inserted between each row of roofing material. Flashing
can also be used as a strip that runs around the dormer and under the
roofing material. Unlike other windows in your home, the flashing is
also extended into a front apron, which overlaps the roof material.
As dormer size and window style vary from house to house, the details
can be different for your house. Flashing overlaps roofing material;
Skylight: Flashing around skylights is usually a continuous piece.
Skylights are raised using a wood curb, allowing enough room for flashing
material. The National Roofing Contractors Association recommends that
this is an 8-in (200-mm) vertical run, If you are re-roofing your house
you may need to raise or remove your skylight for the installation
of proper flashing. Even if your skylight is manufactured with flashing
attached, you may need additional flashing. One-piece flashing.
No matter the shape of your roof, vents are a common feature of any
roof structure. If you are roofing around an already-installed vent,
you may need to alter the height of the flashing detail around the
vent. If you are cutting out a hole in your roof to accommodate a new
vent, be careful to cut a clean hole, to minimize any extra work that
will be needed to complete your project.
Hood vent: Hoods can vent through the wall or through the roof. In
order to save time, materials, and potential for problems, always choose
the shortest option for venting. Shown here is a roofing option. If
you are installing a new vent, you will be cutting a hole in the roof.
After placing the vent in the hole, slip the flashing flange under
the shingles above the vent. The flashing will be over the shingles
below the vent. Seal the joints. Place the vent cap on top of the vent.
Pipe vent: When you are roofing around a pipe vent (also called a
pipe stack), you will need to cut out the shape of the pipe from the
row of shingles. Fit the shingle row around the bottom part of the
pipe. Then, slide pipe flashing over the pipe so that it extends 4
in (100 mm) below the pipe, 8 in (200 mm) above the pipe, and 6 in
(150 mm) to the right and left. The bottom part of the flashing will
overlap the shingle row, as shown.
Chimney flashing: Metal or PVC-based strips cover the joint between
the roof and the chimney. They are bent in the corner and overlapped
on one side by the edges of the shingles, and on the other by the cap
flashing, which is attached into the mortar joints of the chimney’s
Hard coverings such as tiles do not easily break down, so they can
often be reused. New asphalt tiles can sometimes be laid over old ones,
to avoid stripping a roof; ask for your supplier’s advice.
If you are considering changing the type of roof covering, find out first
whether the new roof can be supported by the existing structure. Get
advice from a professional roofer. You may want to consult with more