Roof Cleaning in New Haven
Black streaks on a roof are algae, not staining, and moss on a shaded slope is the stage after that. Both come off with a treatment applied from the edge of the roof, at no pressure, with nobody walking your shingles.
The black running down a north slope is a colony of algae that lives on the limestone filler blended into asphalt shingles. It arrives on the wind, lands everywhere, and survives only where the surface stays damp long enough. That is why the streaking starts on the north face and why it follows the path water takes off the roof. In the plats that went up around the time New Haven Elementary opened in 2004, the shingles are now the right age for it, and even with no trees over them those north slopes hold dew into the late morning.
Two parts of the village push it along faster. The old blocks near Main St sit under a canopy that has been growing for a century, and a roof that spends the morning in shade with leaf litter in the valleys grows moss as well as algae. Moss holds water like a sponge against the shingle and lifts the edges as it thickens. Lots along the Salt River and the low ground toward Lenox Township stay humid, so those roofs are still wet after the rest of the village has dried. Roofs facing 26 Mile Rd also collect road dust, which gives the algae something to hold onto.
The treatment is chemical and slow by design. A solution suited to asphalt shingles goes on from the roof edge, kills the colony where it sits, and then rain does the rest over the following weeks, so the roof keeps improving after we leave. Nothing is scrubbed and nothing is pressure washed. Pressure would take the granules off along with the algae, and those granules are what shields the asphalt from sunlight. Roof treatment starts at $450 and holds three to five years before the next round.
Treated From the Edge, Not From the Ridge
We start at ground level, reading slope, exposure and where the moss is heaviest, and we check the gutters, since whatever is on the roof ends up in them. Plants below the eaves and along the drip line get soaked before anything goes up. The solution is applied from ladders at the roof edge with equipment that carries it across the slope without force, working with the pitch so it covers evenly instead of running off in lines. Downspouts are flushed at the end. On a house with heavy moss we plan a second visit rather than pushing the first application harder. Treatment starts at $450.
What a Pressure Washer Does to Shingles
Asphalt shingles are covered in ceramic granules, and those granules are what keeps ultraviolet light off the asphalt underneath. A pressure washer takes them away by the handful, which is why a roof cleaned that way looks bright for a season and then ages quickly. The other damage is underfoot. Walking a roof in summer heat, especially one with moss on it, breaks the seal strips between courses and creates the leak that shows up in the next hard rain.
Timing It Right
Spring and fall are both good, and anything above freezing works. Moss is easiest to treat in spring, while it is actively growing and holding water, because it takes the solution up faster. If the roof is due and the gutters are due, book them together: the roof is treated first and the gutters cleared afterward, so the debris that comes down goes out with the rest.
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Roof Cleaning in New Haven: FAQs
The roof still looked dark the evening you finished. Is that expected?
Yes. The algae is dead at that point, but the black residue stays on the granules until rain works it off, which usually takes two to six weeks depending on the weather. Heavy moss sheds over a longer stretch as it dries and loosens its grip. Nothing else has to be done in the meantime.
Does anyone have to walk on the roof to do this?
No. The treatment is applied from ladders at the edge with equipment that reaches across the slope, so the shingles carry no foot traffic. That matters most on the older roofs on the village blocks, where summer heat leaves shingles soft enough that a boot print can break the seal between courses.
Why is the streaking only on the north slope?
Because that side stays damp the longest. A south slope dries within an hour or two of sunrise and the colony cannot hold on. North slopes keep dew into the late morning, and on lots near the Salt River or the low ground in Lenox Township they stay damp longer still. We treat every slope anyway, since spores land on all of them.
We may replace the roof in a few years. Is treating it now worth the money?
Usually yes, at $450 against the cost of a roof. Algae and moss hold moisture against the shingle and speed granule loss, so clearing them buys time on a roof that still has life in it. If the shingles are curling, cupping or bare in patches, we will tell you it is past the point where a treatment changes anything.
More in New Haven
Deeper reading: What Are Those Black Streaks on My Roof? (And Why You Shouldn't Ignore Them) and Why Fall Gutter Cleaning is the Cheapest Roof Insurance You Can Buy.
Book Roof Cleaning in New Haven
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