Roof Cleaning in Delaware, Chester, Montgomery & Bucks County
Black streaks are a living organism. We kill it instead of scrubbing the granules off.
The black streaking running down asphalt shingle roofs across this area is Gloeocapsa magma, a cyanobacteria that feeds on the limestone filler in modern shingles. It is not dirt, and it does not wash off. Pressure washing a shingle roof strips the ceramic granules that protect the asphalt underneath and will void most manufacturer warranties.
The correct method is a no-pressure soft wash: a solution applied at low volume, given time to work, and rinsed. The organism dies, and the streaking releases over the following weeks of normal rain. On slate and cedar the same principle applies with a gentler chemistry, because those materials are far more expensive to replace than to maintain.
What algae and moss actually cost you
Algae holds moisture on the shingle surface. Persistent moisture accelerates the loss of granules and shortens the effective service life of the roof. The difference between replacing at year 18 and replacing at year 25 is a real number on a Main Line roof.
Moss is worse. It roots into the seam between shingles and lifts the edge, which lets wind-driven rain under the course. On north-facing slopes shaded by mature trees, moss is the failure mode we see most often, and it is almost always on the slope nobody looks at from the driveway.
Slate and cedar roofs, common on older homes here, will outlive several asphalt roofs if the biological growth is kept off. Neither material tolerates foot traffic well, which is precisely why drone delivery matters on this service.
Signs your home needs roof cleaning
- Dark vertical streaks running down from the ridge
- Green fuzz or clumps along the north-facing slope
- Moss growing in the seams between shingle courses
- Granules collecting in the gutters or at the downspout splash block
- Discoloration concentrated under overhanging tree limbs
- Neighboring roofs of the same age that look noticeably cleaner
How we do it
Roof and slope assessment
We identify the roofing material and its condition first. A roof at end of life, with curling or missing shingles, should be replaced rather than cleaned, and we will say so.
Gutter and landscape prep
Downspouts are diverted and beds beneath the drip line are pre-wet and covered so the rinse does not concentrate on one shrub.
No-pressure application
Solution applied by drone from above the roof plane. Nobody walks the slate, nobody sets a ladder against the gutter, and there is no pressure on the shingle surface.
Dwell and rinse
Dwell time, then a light rinse. Streaking continues to lighten over the following few weeks as rain carries the dead organism off.
Where we do roof cleaning
We serve Delaware, Chester, Montgomery, and Bucks County. Each town page explains what we actually see on homes there — the housing stock, the tree cover, and the schedule that makes sense for it.
Roof Cleaning questions
Will roof cleaning void my shingle warranty?
Pressure washing generally will. No-pressure soft washing is the method the asphalt shingle industry recommends, and it does not disturb the granule layer. If you have documentation from your manufacturer we are happy to work to it.
How long until the roof looks clean?
Most of the improvement is visible the same day. The remaining shadow of the streaking clears over two to six weeks as rain washes off the dead growth. Heavy moss can need a second visit the following season.
Can you clean a slate roof?
Yes, and slate is one of the strongest reasons to use a drone. Slate cracks under foot traffic and a cracked slate is an expensive repair. Cleaning from above the roof plane means no weight on the tile at all.
How often should a roof in this area be cleaned?
Every three to five years for a roof in open sun. Every two to three years for a north slope under mature canopy, which describes a lot of homes in Wayne, Valley Forge, and Bryn Mawr.
Do you install zinc or copper strips?
We do not install roofing hardware. If your roof is a repeat-growth candidate we will tell you where a ridge strip would help so you can raise it with your roofer at the next repair.