Can You Pressure Wash a Roof?

The short answer

A pressure washer will clean a roof, and it will also take years off it. Asphalt shingles are protected by mineral granules embedded in the surface during manufacture. Those granules block UV, and once they are gone the asphalt underneath degrades quickly. High pressure removes them in quantity. That is not a risk of doing it wrong, it is what happens when it is done at all.

How to tell it has already happened

Look in the gutters and at the base of the downspouts after any roof work. A layer of coarse dark grit means granules came off. Some granule loss is normal over a roof life, but a visible accumulation right after a wash is not weathering, it is damage. Bare patches, a shinier look in places, and shingle edges that have lifted are the other signs.

Most manufacturer warranties exclude damage from pressure washing, so it is worth checking yours before letting anyone near the roof with a machine.

The other damage

Granule loss is the headline, but not the only issue. Shingles are designed to shed water flowing downward. Spraying up under the courses drives water the wrong way, past the shingle and onto the deck below, where it can reach the underlayment and the sheathing. Around flashing, vents, and valleys the risk is higher still. On older shingles that have gone brittle, pressure can crack them or lift them off their seal.

What the dark streaking actually needs

The black streaking is algae, a living organism rooted in the shingle surface. Force removes what is visible and leaves the roots, so it comes back quickly. A cleaning solution kills it, which is both gentler and longer lasting. A soft wash applies that solution at roughly garden hose pressure, gives it time to work, then rinses gently.

The roof continues to lighten for a week or two afterwards as rain carries the dead growth off. Expecting an instant result is what pushes people toward pressure in the first place.

Metal, tile, and slate

Shingles are the common case but not the only one. Metal roofs can be damaged around seams and fixings and the coating can be dulled. Clay and concrete tiles crack and dislodge under pressure, and walking a tile roof causes more breakage than the washing does. Slate is brittle and expensive to repair. All of them are soft wash surfaces.

What we do

We soft wash roofs. We do not pressure wash them, on any material, and we protect the planting below before the solution goes on. Call (504) 688-3995 for a free written estimate.