After a Disaster Roof Repairs 4: Flashing & Sealing

Publication Number 490-325, August 1996

General

A hurricane or heavy storm can stir up a lot of damage! Even in the best of times, though, moisture and termite damages cost $2 billion to $3 billion per year in housing dollars nationally. For many people, repairs after a disaster can correct some previous causes of moisture damage to roofs, increasing the value of our homes.

On the roof, pay particular attention to penetration; for example, plumbing sewer vent pipes, skylights, fan exhaust covers (range, bath, etc.), chimneys, dormers. Anything that actually comes up through a roof is critical. Flashing is needed in roof valleys and on roof edges. Thus, penetrations, valleys, and edges of the roof need careful attention to preserve a roof. Consider each:

Roof Penetration: Specific printed instructions are provided by the asphalt shingle manufacturer. Use and follow these instructions in the packages of shingles applied to your roof.
Roof Edges: When water runs down your roof, especially in a slow rain, it pauses a moment before pouring off. At the moment of pause, it runs back under the edge of the shingle, often reaching the edge of the sheathing, wetting the sheathing. As this happens repeatedly over the years, the sheathing rots.
This may be prevented in a number of ways. The simplest method is to edge the roof deck (sheathing) with metal. Fit preformed metal drip edging snugly against the fascia (edge) board at the eaves (edge) of the roof. Nail it every 12 inches with roofing nails centered in the top surface of the metal. Do this on the "downhill" edge before applying the #15 felt underlayment. After applying the underlayment to the entire roof, install the metal drip edge to the roof rake edge (sloping, gable end edges).
Roof Valleys: There are several methods of adequately waterproofing valleys. The important thing is that they be given the special attention required. Some methods are:
- Use 28-ga. galvanized, corrosion-resistant metal, minimum. Extend the metal from the center line of the valley a minimum of 8 inches each way from the center. Sections must be jointed to provide adequate waterlock.
- Woven or closed valleys may be constructed by centering 36-inch wide, no less than #50, roofing felt (tar paper) in the valley over the basic #15 felt (tar paper), or
- If the valley is made of laced composition shingles, #30 felt (tar paper) extending 10 inches from the center line each way is acceptable, or two layers of #90 mineral-surfaced cap sheet cemented together with the bottom layer not less than 12 inches wide laid face down and the top layer of not less than 24 inches wide laid face up.

Only a water-tight roof is considered an adequate roof. Inspect the job carefully and seal any little place questioned with roofing cement (asphalt). Moisture control problems are the biggest maintenance job we encounter. Prevent future problems now.

Based on information developed by Clemson Cooperative Extension following Hurricane Hugo. Revised for Virginia audiences by Virginia Cooperative Extension.

For more information, contact your local office of Virginia Cooperative Extension.

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