Once you know your roof has algae, the next question is usually what to actually do about it. Two answers come up constantly: install zinc strips, or get the roof professionally cleaned. Homeowners often treat these as competing options, as if you have to pick one. In reality they solve two different problems, and most roofs with a real algae history need both. This guide breaks down what each one actually does, where each one falls short on its own, and how to combine them so streaks stay gone instead of creeping back within a year or two.
Two Different Jobs: Prevention vs Removal
The simplest way to understand the difference is this: cleaning removes what is already there, and zinc strips slow down what grows back. Confusing the two is the most common mistake homeowners make, and it explains most of the disappointment people report with either method.
If your roof already has visible black streaking, installing zinc strips by themselves will not make that streaking disappear. The strips work going forward, on new growth, not on algae that has already colonized the shingle surface. On the other hand, a professional cleaning will remove existing streaks, but without some form of ongoing prevention, new algae spores will eventually land, settle into the same shaded, damp conditions, and start the whole process over again.
How Zinc Strips Actually Work
Zinc strips are thin metal strips installed near the roof ridge, typically tucked under the cap shingles so only a small edge is exposed to rainfall. Every time it rains, water running over the strip picks up microscopic amounts of zinc and carries them down the roof slope. That trace zinc creates an environment that algae and moss have a harder time establishing in.
What zinc strips are good at:
- Slowing new algae growth on the area of roof below the strip
- Providing years of passive protection with no ongoing cost or effort
- Extending the time between cleanings, often meaningfully
What zinc strips cannot do:
- Remove algae that is already established on the shingles
- Protect areas far from the ridge as effectively, since the zinc concentration thins out the farther water travels down the slope
- Stop moss, which tends to respond less to zinc than algae does and often needs physical removal
Properly installed strips, placed correctly under the cap shingles, do not damage the roof and are generally compatible with manufacturer warranties. Problems usually trace back to poor installation rather than the strips themselves.
How Professional Roof Cleaning Actually Works
Cleaning takes the opposite approach. Rather than preventing future growth, it targets the algae that is already on the roof. A proper low pressure cleaning applies a solution designed to kill the organism at the surface, lets it dwell long enough to work, and then rinses gently rather than blasting the shingles with force.
What cleaning is good at:
- Removing visible streaks and restoring the roof’s appearance
- Treating moss as well as algae, which zinc strips handle poorly on their own
- Giving an immediate, visible result rather than a slow preventive effect
What cleaning cannot do:
- Stop new spores from arriving and starting the growth cycle again
- Provide any lasting protection once the cleaning solution has worn off
- Fix the underlying shade and moisture conditions that caused the growth in the first place
It is worth repeating a point that matters for anyone tempted to handle this themselves: pressure washing is not the same as proper roof cleaning, and it is one of the most damaging things you can do to an asphalt shingle roof. The force that strips away algae also strips away the protective granules on the shingles, and it can drive water up underneath them. Most shingle manufacturers do not approve pressure washing as a cleaning method, and using it can void your warranty. If you want the full breakdown of what causes roof algae in the first place and why New Hampshire’s climate has made it so much more common in recent years, see our guide on black streaks on your roof in NH.
Why New Hampshire Roofs Often Need Both
Black roof algae used to be rare this far north. Within the roof cleaning industry, several New England contractors have reported that algae went from an occasional problem to a widespread one over the last several years, as warmer, wetter weather patterns created better conditions for it to spread. Algae spores also travel on wind, which is why it is common to see one roof in a neighborhood develop streaking and then watch several nearby roofs follow within a season or two.
That combination, a region where algae used to barely exist now dealing with it constantly, plus a spore source that keeps replenishing from neighboring roofs, is exactly why a single approach tends to disappoint. Cleaning alone means repeating the whole process every year or two. Zinc strips alone leave existing streaks in place and do little for moss. Used together, a roof gets cleaned once to remove what is there, and strips are installed at the same time to slow down how quickly it returns.
A Practical Combined Approach
For most New Hampshire homes dealing with algae, this sequence gets the best long term result:
- Start with a professional inspection. Confirm whether you are dealing with algae, moss, lichen, or some combination, since the right treatment differs for each.
- Clean the roof properly. Low pressure application with an appropriate cleaning solution, not a pressure washer, removes the existing growth without damaging the shingles.
- Install zinc strips at the same visit. Adding strips right after a cleaning means the roof starts its clean slate with ongoing protection already in place, rather than waiting until streaks reappear.
- Keep gutters clear and branches trimmed. Zinc strips and cleaning both work better when the roof also gets reasonable sun exposure and airflow, so trimming overhanging limbs supports whichever treatment you choose.
- Plan for periodic rechecks. Even with strips installed, heavily shaded roofs may need a lighter cleaning every few years. Roofs with better sun exposure often go much longer.
If you are not sure which situation applies to your roof, our roof cleaning and coating service covers how we handle both the cleaning and prevention side of this, including where zinc strips fit into the process.
When Neither Option Is Enough
Both zinc strips and roof cleaning assume you are working with a roof that is otherwise in good condition. If the algae or moss has been present for years and is accompanied by curling shingles, heavy granule loss in the gutters, soft spots, or active leaks, cleaning will improve the appearance but will not address the underlying wear. In that situation, the more useful conversation is about roof replacement rather than ongoing maintenance.
Frequently Asked Questions
Do zinc strips really work on roof algae?
Yes, but only for prevention, not for removing algae that is already there. Rain carries trace amounts of zinc down the roof slope below the strip, and that zinc discourages new algae and moss growth. Strips installed on a roof that already has heavy staining will not clean the existing streaks.
Can I install zinc strips without cleaning my roof first?
You can, but the existing streaks will remain visible, and the strips will not remove them. Zinc strips only prevent new growth going forward. If you want the roof to look clean again, it needs to be cleaned first, with strips added afterward to keep it that way.
How often does a roof need professional cleaning?
It depends on how much shade and moisture the roof gets. Heavily shaded, tree covered roofs may need cleaning every one to two years, while roofs with good sun exposure and zinc strips installed may go three to five years or longer between cleanings.
Do zinc strips damage shingles or void warranties?
Properly installed zinc strips, placed under the cap shingles near the ridge, do not damage the roof and generally do not affect manufacturer warranties. Problems come from poor installation, such as strips nailed incorrectly or placed in a way that allows water to get underneath them.
Is roof cleaning alone enough to prevent algae from coming back?
Cleaning alone removes existing growth but does not stop new spores from landing and establishing again, especially on shaded, humid roof slopes. Pairing a cleaning with zinc strips or a similar ongoing treatment gives far better long term results than cleaning by itself.
Get a Plan Built for Your Roof
Whether your roof needs a cleaning, zinc strips, both, or something more, depends on how long the growth has been there and what shape the shingles are in underneath it. Nick Tracey Roofing offers free, no obligation inspections across New Hampshire and Massachusetts, and we will tell you honestly which combination makes sense for your home. Contact us to schedule a visit.
