Pressure Washing Asphalt Shingles

As I sit here on the precipice of typing out a post about pressure washing composition/asphalt roofs, I have to weigh the facts with great caution. This is not quantum physics and we have been doing this for over 25 years in the Seattle/Bellevue, so why would I have any reservations about writing a professional opinion about low pressure washing of composition roofs? Simply put, NOT all roofs, pressure washing equipment and laborers are measured equally. I’ll get into these later, but lets’ look at some of the basics.

Most composition roofs have exclusions in the manufacturers warranty for any type of aggressive cleaning of the roof surface, be it low pressure washing or pressurized air cleans. The first thing you need to know about warranties are that they are set up to offer the manufacturer as many out clauses as possible, this is business 101, eliminate the amount of risk for a product.

Exclusions to low pressure washing maintenance is just one of many (if you actually read the fine print) that manufacturers like to use to void the liability of the roofing material. This is not without some merit, however, as we have seen many roofs severely damaged from pressure washing and air cleaning. When done right a low pressure washing of a composition roof should produce no more granule loss than a normal rain cycle.

If you look in your gutters after a normal rain and see granules, this is what it would look like after a professionally cleaned roof would look like.

When done wrong, the roof could be completely torn up and need replaced. That’s quite the variance and one that should not be overlooked, but far too often people do overlook these differences and either get very poor work or have trouble ever ridding their roofs of moss. One more thing to consider about manufacturers warranties are that these warranties are written for a product that is sold nationally, so all the rules and exclusions apply the same in Phoenix as they do here in Seattle. Well, that’s great for the manufacturer but for those of us who actually have to maintain a roof in a temperate rain forest, it sure makes it harder to keep moss, lichen, algae and fungus under control. Airborne algae like Gloeocaspa Magma releases spores and induces other growth of other algae, moss, fungus and lichens, and is very common in the Pacific Northwest. Due to the root systems of these different moss and algae growths, the only method of removal of these spores and microbes is a pressure washing, and that is the reason for this article.

Before I list some of the things to look for in a professional roof maintenance co, I do want to add that before any cleaning can be done, make sure the company has looked at the roof and qualified it for a roof cleaning. Older roofs or roofs that are in poor condition may have severe balding or granule loss, which immediately disqualifies these roofs for any type of aggressive cleaning methods, these roofs should just hold out until they can be replaced. For those roofs that do qualify, here is the tale of the tape.

First and foremost find a qualified, licensed, insured and bonded roofing or roof maintenance contractor. Check the trade journals (we use the Bellevue Business Journal), L&I website for any issues for a prospective company, if there are any current or lingering issues from past work or liens, you will hopefully be able to spot them before you sign any contracts. Do not have your friends neighbor or your own children go up on the roof with a pressure washer from Home Depot, not only is that person at risk for falling off and injuring themselves, but without the proper equipment there is an almost 100% certainty that there will be lines in the shingles and possibly deep grooves into the fiberglass of the roof, at this point your roof is ruined.

Once you have found your roofing company of choice, they should have a very similar set up as we have. Although each company operates differently, here is a brief synopsis of what will be needed to do a good composition roof clean and treatment with no damage to roof.

• High Volume Pressure Wash Pump-10-15 gallons per minute (most of these types of pressure wash systems cost between 3,000.00-7,000.00, not your Lowes or Home Depot variety for sure)
• 1500 psi or less with 10-15 gallons per minute
• Use of 35-40degree tips, stay away from smaller tips (which control the spray pattern)
• Positioning of the wand and direction of spray-45 degree angle and 8″ to a foot distance from shingles
• Knowing your way around a roof and it’s penetrations-This is especially true around skylights and other areas that may allow water entry, the technician should always with back facing the skylight wash from edge of skylight outward (away from skylight) never allowing the spray to get near the flashing or skylight housing. If moss is present around skylight housing, hand clean these areas and use treatment to eliminate the moss.
• Spray direction-usually best course of action is directing spray down, working your way down the roof from ridge to eave as to not allow the pressure to lift the shingles or break the seals. Many times these seals are already broken from the moss and spraying up the roof may actually blow the shingles off. A good technician will notify the customer or company office of loose shingles before proceeding. Sometimes a directional spray going up the roof is required to get the moss on bottom edges or lips of shingles, as long as the shingles are sealed and not lifting, and tip is held back a bit further, this should be fine. This is rare and only occurs with very stubborn moss growth.

Pressure Washing vs Chemical Treatments

The alternative to pressure washing is using chemical treatments that kill the moss and allow if to slough off or to be removed once it dies. This method can be effective without having any pressure of water or air on the roof and eliminates user error. Another advantage over pressure washing is that if roof pitch is low enough a home owner can apply the treatment themselves, eliminating cost of a roof maintenance company and aggressive methods of cleaning. Moss treatments come in many varieties and depending on how severe the amount of debris that falls onto a roof is, will determine how many treatments will be needed to keep moss away. If your roof gets blasted with needles and leaves year round, then you will need to first, have all the debris blown off regularly. Debris sitting on a roof is the #1 cause for moss and spore growth, and needs to be kept as clean as possible. Once the debris is removed, by home owner or contractor, then a proper application of a mossicide is required.

• Zinc Sulphate-One of the more prevalent moss chemicals is Zinc Sulphate. this type of chemical is usually in a powder form and can be bought in different grades (consumer or industrial). Most customers will recognize Moss Off from Home Depot, this moss killer has the Zinc Sulphate as it’s active ingredient. We use a more industrialized brand, but it’s effectiveness is relatively the same. We use this chemical more as a follow up to a pressure wash in our Clean and Treat Package, it helps in fighting the residual root systems that may have been left behind on the lips or edges of shingles. It can be applied dry and just sprinkled on the roof or diluted with water and sprayed on as a flood coat. When sprinkled on the roof you may see white powder on roof for several days to weeks until the chemical washes completely down the roof. Usually it is applied at the ridge lines and through the middle of roof, in a continuous line, some people just toss it around like grass seed, everyone’s different. Once applied, the moss should start dying within a few days, usually indicated by the moss turning brown or black, if the moss is still green after a week or two, then most likely you will need to do a second application. Zinc is not the greenest chemical for moss treatment, as it will kill some plants and is not safe for water systems, like ponds, lakes or streams, however, it is so commonly used that most people never think about it’s effects long term (isn’t that the case with everything in todays world?).
• Clean Brite-This is a more environmentally friendly chemical treatment. It’s active ingredient is a fatty acid, like crypticidal soap. It is not as easily applied like Zinc as it needs to be diluted and sprayed on through a pressure washer or a pump system. It is a bit more aggressive and effective treatment, but the costs are more as well. We usually charge for these types of treatments when we do a roof cleaning. We offer a Zinc treat at no cost following a pressure wash job because it is a shorter lasting treatment, Clean Brite will stay on a roof for a longer period of time as opposed to Zinc.
• Sodium Bicarbonate-basically baking soda. While this is the most environmentally friendly moss treatment used, it is also not nearly as effective. It more often than not needs to be applied more than once and requires a follow up roof top visit where some brushing and scraping is needed to rid the roof of moss. For very light algae or moss, this may be the cheapest and safest method of treating the moss, for more problematic roofs, it is not really a viable option.
• Copper Napthanate-This moss treatment is very effective in killing moss, it also is very effective in killing your workers and animal life surrounding the home as it is very toxic and many times requires a mask when applied. We try to stay away from using this chemical at all costs.
• Bleach, Tide, Vinegar and other home remedies-Outside of vinegar, we don’t suggest using any of these products on your roof. The bleach will potentially stain your roof and it is not environmentally friendly at all. Your roof may smell nice, but more than likely it will have minimal effect on long term moss removal and your plants around your home will wither away with runoff from gutters. Vinegar is an interesting solution and if I could get a success rate close to that of Zinc or Clean Brite I would use it religiously as it is great for the environment, and cheap. Any success stories, let me know.
• Zinc Strips-Not a chemical treatment per se, but commonly referred to as one. Zinc strips will work from the ridge down about 10 feet. Then over a period of 3-5 years they lose their effectiveness and become a liability to the roof system. They penetrate the roof with nails and will pull off and flap away in strong winds. Not ideal, as a roofing installation company, we hate seeing these Zinc Strips on a roof as we have seen too many at the source of leaking. We probably would not install these unless a customer absolutely insisted on them.

These are just a few of the many chemicals on the market for treating moss and fungus on composition or asphalt roofs. Just doing a chemical treatment on a mossy roof is a time invested process that has very mixed results and can be frustrating, which is why there is a viable reason to consider using a low pressure wash over a strict chemical treatment. Here are 3 main reasons why a Low pressure wash may be your best solution for moss removal, there are more, but these are the big 3.

1. Immediacy-Same day removal, when we leave, your roof is moss free and looks like it did when it was new. It not only removes moss, but it removes ugly stains and beautifies the roof as well.
2. Thorough-A low pressure wash will, if done right, remove the underlying and hard to see, root systems that can get left behind in chemically treated roofs. these root systems are the culprits in releasing of more spores and causing a regeneration of moss growth. With our Clean and Treat service, we actually do a follow up Zinc treat to ensure as minimal of regrowth happens as possible.
3. Dormant Moss-When a roof is chemically treated the moss is left behind, which will attract moisture, even if it is dead or dying. this is not ideal when dealing with the type of weather and moisture we have in the Northwest, this could easily cause more spore growth while waiting for the chemical to do it’s job.

So, there is a start for your research into what type of moss removal you will likely pursue for your particular roof. Everybody’s situation is unique and not all removal systems apply across the board. We can help guide to to the direction that works best for you. this article is more of a guide and hopefully answers many of the questions we receive on a daily basis. One more added advantage of a low pressure washing is that it will also include a washing of the gutter system, which is a large source of spore growth. Any time a low pressure wash service is done it should include the gutters. It also makes the clean up much cleaner, leaving the home or property usually much cleaner than it was before we arrived.

What you can expect from a low pressure clean and treat service is a roof to be moss free for a period of 2-5 years. the variance depends on shading, debris and effectiveness of treatment post cleaning. Some roofs will be moss free for up to 5 years before new spores begin to grow. Other roofs could see moss growth as soon as 1 year later if roof is not maintained properly (keeping roof free of debris). Typically we see most roofs last 2-3 years before any new growth occurs, that is assuming no treatments have been done since the cleaning. If a customer follows a regular blow off and treatment plan after a pressure washing service, then this can extend the need to do another cleaning for several years.

We hope this helps and welcome anyone interested in using our services for any type of moss removal.