Yorktown NY Roofing: Article About Flashing On Roofs
Flashing is material that is fastened to seams on a roof to keep water from penetrating. Valley flashing is the type of flashing that is fastened to the seams of valleys formed where two sections of the roof meet. More water runs down these seams than other parts of the roof, so it is important that they be watertight.
Yorktown NY roofing professionals fasten valley flashing to a roof after the sheathing and felt paper but before the shingles or shakes. In many cases, more felt paper is used in areas under valley flashing than the rest of the roof in order to provide additional protection from water.
Valley flashing is generally made of galvanized steel or aluminum. It can be painted. If it is painted and crimped in the center, the crimp must be touched up with paint afterwards. It extends for 6 to 10 inches on either side of the seam created by the valley. The less steep the slope of the roof, the longer it should extend.
A drip edge is another type of flashing. This is preformed metal attached to the end of eaves to keep water running down the roof from penetrating back under the shingles. It is nailed to the sheathing of the eaves, but not the fascia, before felt paper is put down at 8 to 10 inch intervals.
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It is also nailed down along rakes at the same intervals.
Vent collars are used to cover up objects poking through the roof and are commonly used with plumbing vents. The latest type of vent collars has a preformed rubber collar that slips over the pipe and forms a seal. A piece of flashing at the bottom makes the watertight connection with the roof. This flashing tucks beneath the shingles on the high side of the vent and lays above them on the low side.
Step flashing is used around chimneys and walls. Each piece of step flashing overlaps the next, and it is tucked under shingles. It comes precut, or it can be cut to a length of 10 inches long and 2 inches wider than the seam being covered. The high side around a chimney is nailed down, but the low side is not.
For the most part, nails must be of the same material as whatever flashing they are being used with. This is to prevent corrosion between different types of metals. This is a danger when working with copper in particular. Flashing metal of all types is very sharp, so gloves should be worn when cutting.