Roof moss removal cost

Removing moss from a roof by hand costs $0.60 to $1.00 per square foot, typically about $0.80. A soft wash that kills moss and algae without brushing runs $0.15 to $0.60 a foot, and most roofs that need one need some of the other.

What moves the bill is not the size of the roof but how much of it is covered and how thick the growth is. A thin film on one shaded slope is a soft wash. Cushions of moss packed into the shingle joints are hand work, and that is where the price, and the risk to the shingles, both go up.

What it costs

The per-foot rates are measured on the area treated, not the whole roof. Most crews also have a minimum charge for the visit, so a small patch costs more per foot than a whole slope.

Why moss is a roof problem, not a stain

Algae streaks are a discoloration. Moss is a plant, and it works on a shingle roof in three ways.

It holds water. A mat of moss stays wet for days after rain, so the shingles under it never dry. On a north slope in a wet climate, that can mean the surface stays damp for most of the cool season.

It grows into the joints. Moss starts in the gaps between tabs and along the lower edges of each course, where grit and debris collect. As it thickens, it pushes up the edge of the shingle above, breaking the seal that holds it down and opening a path for wind-driven rain.

It wicks water uphill. Packed into the overlap between courses, moss acts like a wick and draws water up and under the shingle above, past the point where the roof was designed to shed it.

In cold climates, add freezing. Water held in the moss and the lifted edges freezes and expands, and each winter pries the shingles a little further apart. None of this happens quickly, which is why moss is easy to ignore until it has been there for years.

Manual removal against soft wash

The two methods are not alternatives so much as two steps, and good crews often use both.

Manual removal is a crew on the roof with soft brushes and plastic scrapers, pushing moss off in the direction the water flows, top to bottom, never upward against the shingle edges. Pushing upward catches the lower edge of each course and lifts it. The work is slow, it needs a dry day so the roof is safe to stand on, and the rate reflects that.

A soft wash is a low-pressure application of a cleaning solution that kills moss and algae, left to sit and then rinsed. It does not remove thick moss on the day. Dead moss loosens and washes off over the following weeks and months of rain, and the thickest clumps may need brushing later.

The usual sequence on a heavily grown roof is to treat first and brush once the moss has died back, when it lifts away with far less force. On a roof with only a thin film, the wash alone is usually enough, and paying for hand work is paying for something you do not need.

The one method that should not appear on a quote is a pressure washer. The roof cleaning guide explains why it strips shingles; on a mossy roof it is worse, because the jet drives water straight into the joints the moss has already opened.

The damage risk to granules

Every method that touches the roof costs some granules. The granules are the mineral coating that protects the asphalt from sunlight, and they are what wears away as a shingle ages.

On a roof in good condition, careful brushing removes a little surface grit and nothing more. On an older roof the picture changes. Moss tends to grow where shingles are already worn, and the granules under a thick mat are often loose. Removing the moss can reveal bare patches that were already there, and a crew can be blamed for wear it uncovered rather than caused.

Ask the crew to photograph the worst areas before they start. Check the gutters and the ground below the eaves afterward: some grit is normal, but heavy drifts of granules mean either rough work or a roof near the end of its life. If it is the second, moss removal buys appearance, not years.

When moss means a leak

Moss itself does not puncture a roof, but heavy, long-standing growth is a good place to look for one. The signs that it has already let water in:

Stains in the attic on the underside of the deck below the mossiest slope, or on the rafters near it. Look on a bright day with the attic light off.

A soft feel underfoot when the crew walks that area, which can mean wet or delaminating decking under the shingles.

Lifted, cracked or missing tabs once the moss is off, especially along the lower edges of courses.

Moss packed into valleys or along the uphill side of a chimney or skylight, where the most water runs and the flashing sits.

A crew that finds any of these should stop and tell you rather than brush and leave. An inspection at $150 to $400 confirms what is under the growth, and the roof repair guide helps with whether to patch or plan for more. An isolated leak is usually a modest repair; several lifted areas on an old roof can be the first conversation about replacement.

Keeping it from coming back

Cut the shade. Moss grows where the roof stays damp and dark. Thinning or lifting the branches over a north slope lets the roof dry after rain, and it does more than any treatment.

Zinc or copper strips. A strip fixed just below the ridge, and below each hip on a hipped roof, sheds trace metal into the rainwater that runs down the slope. The effect is strongest close to the strip and fades farther down, so on a long slope a second row partway down may be needed. Copper is generally more effective than zinc and costs more. Strips have no price item here; ask for them as a separate line.

Keep the gutters clear. Moss washed off the roof ends up in the gutters and downspouts, and a clogged gutter holds water against the roof edge. Clean them after any removal job, and see the gutter guard guide for what guards can and cannot keep out.

Plan the next roof. When the roof is replaced, algae-resistant shingles and a little more sun on the north slope will do more than any number of treatments on the old one.

A worked example: one mossy slope

A 2,000 square foot roof where the north slope, about 900 square feet under a large maple, is thick with moss, and the rest has a light film of algae. The owner wants an inspection because the moss has been there for years.

• North slope, hand removal: 900 sq ft × $0.60 to $1.00 per sq ft = $540 to $900
• Remaining slopes, soft wash: 1,100 sq ft × $0.15 to $0.60 per sq ft = $165 to $660
• Inspection with attic check: $150 to $400
• Total: $855 to $1,960

The hand work is the largest line at $540 to $900, and it is limited to the one slope that needs it. Pruning the maple would be a separate bill at $250 to $1,000, and without it the north slope is likely to need treating again within a few years. If the inspection finds a lifted section that is leaking, the repair is quoted on top.

Frequently asked questions

How much does it cost to remove moss from a roof?

Typically $0.80 per square foot for hand removal of the affected area, and less for a soft wash where the growth is light. Expect a minimum charge for a small job.

Does moss on a roof mean it needs replacing?

Not by itself. Moss on a sound roof can be removed and kept off. It points to replacement when removal reveals widespread granule loss, lifted or cracked shingles, or soft decking, especially on a roof near the end of its rated life.

Can I remove roof moss myself?

From a ladder at the eave, with a soft brush and working downward, a small patch is manageable. Walking a wet, mossy roof is dangerous, and anything beyond the first few courses is a job for a crew with fall protection.

How long does it take for moss to die after treatment?

Usually several weeks, sometimes longer in cool weather. The moss turns brown and loosens, and rain carries most of it off over the following months.

Related guides

• Roof cleaning cost — soft washing, algae streaks and why pressure washing is out
• Roof repair cost — fixing what moss lifted, and repair against replacement
• Roof inspection cost — what a full inspection with the attic looks at
• Gutter guard cost — keeping washed-off moss out of the gutters