Crash Course In Roof Flashing

The majority of my last two years of undergraduate school were spent between Mason Hall and Jim Hartley, two burley roofers who between them did not have enough credits to earn a high school diploma.

But they knew how to lay three-tab shingles, lace a valley, slop hot tar, keep roofs from leaking and what beer to order with a fried egg and tomato sandwich at seven in the morning.

Plus how to pawn the worst jobs at Logsdon Roofing onto the skinny English major. Trust me, they kept me humble.

One of the first lessons Mason taught me was "Standing water doesn't." (That one took me a moment, too.)

What I also learned was probably rooted in a physics class none of the three of us ever took: different materials expand and contract at different rates.

Which is what explains why it is that in the dead of winter you can have water running down the fireplace in your living room. A chimney, as well as a bathroom or kitchen vent pipe or a skylight, requires a hole cut through the rafters, plywood sheathing and asphalt shingles that make up your roof. The gap between the masonry chimney and the roof material is filled with caulking, often around rubber or metal flashing designed to direct water away from the opening.

All of these materials -- metal, masonry, rubber, asphalt and wood -- expand and contract on a daily basis, but not at the same rate. This means the caulking has to remain flexible in order to prevent water from entering your house. The problem is, like standing water, it doesn't.

And when it loses its flexibility, it cracks and then water, either from rain or melting snow blown up against your chimney or skylight, makes its way into your house and onto the drywall, plaster or wood trim on your wall.

Repairs are costly, but a little preventative maintenance is not. If your roof is steep and your knees are weak, hire a professional. But if you can safely climb a ladder and walk on your roof, it only takes a small amount of inexpensive asphalt roof coating or caulking to seal the gap. Here are some quick tips:

1. Wear tennis shoes with good tread to keep from slipping and from damaging your shingles.

2. Wear disposable gloves.

3. Use an old paint brush to clean off the dust on the old flashing.

4. Thinner roof coating adds another layer of protection to good caulking; apply it with a brush.

5. Thicker roof caulking fills large gaps; apply it with a narrow metal trowel.

6. Warm either product by keeping it indoors before you apply it.

7. Never apply when the roof or the old flashing is wet, or when the temperature is below the recommended range on the label.

Good Luck!

- Bruce