Why Painted Roof Pipes Fail in the Bay Area (and What We Do Instead)

A pipe jack, or pipe flashing, is the metal skirt that seals a plumbing vent or furnace flue where it comes through the roof. Most are galvanized steel. On a new roof the crew slides the flashing over the pipe, nails the base under the shingles, and sprays the whole thing with a can of paint chosen to roughly match the shingle color. On the day the roof is finished it looks tidy.

Give it one East Bay winter and one East Bay summer. Winter rain from November into March sits on the flat base of the flashing and runs down the pipe every time it storms. Then the dry season arrives, and from June through September the roof surface bakes in the afternoon sun. The paint dulls first. Then it chalks, so that a fingertip comes away white. Then it lifts in flakes along the top of the pipe and around the base, where the metal moves the most. Adeline's family has been roofing Fremont since 1986, and her rule is simple: a painted pipe starts to show it within the first year. By the third or fourth year it looks like something nobody bothered to finish.

Paint is a thin film sitting on a smooth, slick metal surface, and the roof is one of the hardest places on a house to hold a film like that. Three things work against it.

Heat cycling. A dark shingle roof gets far hotter than the air on a summer afternoon and cools quickly after sunset. The steel pipe and its flashing expand and contract with every cycle, and the paint does not move at the same rate. Over hundreds of cycles it cracks at the tightest bends, which are the top of the flashing collar and the joint where the collar meets the base.

Sun. Ultraviolet light breaks down the binder in ordinary spray paint. That is the chalking you can wipe off with a finger, and once the binder is gone the pigment has nothing holding it to the metal.

Water. Rain runs down the pipe and pools where the collar meets the flat base plate. Once there is a hairline crack in the paint, water gets behind the film and lifts it. Galvanized steel resists rust on its own for a while, but the zinc layer is thin, and every scratch from a ladder, a tree limb or a roofer's boot is a place for rust to start under the paint.

Painting was never meant to be a weatherproof finish. It was a way to make the flashing less ugly for a few seasons.

Here is the part most homeowners never hear. A pipe flashing has two jobs. The collar keeps rain from running straight down the pipe. The base plate keeps water that reaches the roof surface flowing over the shingles below it instead of under them. The weak point is the joint between the two, where the metal has been formed, soldered or crimped at the factory, and where any imperfection in the metal sits.

That joint is also where the water is. Every drop that runs down the pipe lands on it, and every drop that blows across the roof piles against the uphill side of it. Once the paint fails there, rust follows, and rust on a formed seam opens a path. On the Fremont and Newark roofs we repair, a stained ceiling under a bathroom is very often a pipe flashing whose base has rusted through, not a shingle problem at all. We cover what that inspection looks like on our roof leak repair and detection page.

The stone-coated flashings we install are made by California Stone Coating, Inc., a Bay Area manufacturer, and the reason Adeline is so firm about them is that they solve the exact problem described above. Instead of a film of paint, the flashing is finished with a fused coating of stone granules, the same idea as the granule surface on the shingle itself.

That changes several things at once. The finish matches the shingle color, and the manufacturer can blend a custom color for a roof that is not a standard shade. It is designed not to chip, peel or fade the way paint does, so the roof looks finished in year ten the way it did on day one, with no repainting. The coating resists rust, rot, algae and fire. Most important, it helps waterproof and protect the flashing at the base of the pipe, which is exactly where the metal imperfections sit and where leaks are most likely to begin. The coating runs up the collar as well, so there is no silver stub sticking up out of a brown roof.

None of that makes a roof leak-free forever, and we will not tell you it does. It takes the single most common leak point on a shingle roof and gives it a finish that lasts as long as the shingles around it. The full story, with the manufacturer's details and the vents and valleys we finish the same way, is on our stone-coated flashings page.

You do not need to climb a ladder to know whether your pipes are in trouble. Pick a bright morning, stand across the street, and look at each slope with a pair of binoculars if you have them.

Look for color. A pipe that is a different shade from the shingles, or shows silver at the base, has lost its paint. Look for streaks. Rust running down the shingles below a pipe means the flashing itself is corroding. Look for a raised or cracked collar at the top of the flashing, which is the rubber or metal seal working loose. Look at the uphill edge of the base plate for lifted shingles or debris packed against it. And look inside: a faint ring on the ceiling of a bathroom, laundry room or kitchen usually sits within a few feet of a vent pipe above it.

If you see any of that, call before the rain does the checking for you. If you see nothing but want a set of eyes on it, a roof inspection covers every penetration on the roof, not just the pipes.

On a repair, we pull the failed flashing, put a sound new one in its place and reseal the shingles around it. It is a small job, and it is one of the highest-value repairs on a roof because of how often that spot is the whole problem. The stone-coated finish is a different matter: those flashings are woven in under the shingle courses as a roof is laid, so they go on with a full roof replacement, never as an add-on to a roof that is already down. On a replacement, in Union City, Hayward or anywhere else we work, every pipe, vent and valley is finished stone-coated as part of the job, not as an upgrade you have to ask for. That is the standard, and it has been from the day Adeline took the company over.

The Bay Area Rainy Season Roof Checklist walks through pipe bases, valleys and the other spots to check before November.

For the work itself, see stone-coated flashings and roof repair. If you are in our home city, the Fremont roofing page covers the neighborhoods we grew up working in.