Look out for those pencil thin mustaches!

We often tell our clients to call us when they see "pencil thin mustaches" of moss growing at the bottom edges of their shingles. By catching the moss at this early stage, you can maintain your roof without ever needing to aggressively clean your roof. Around the home, we prefer chemicals that do not include herbicides or metals such as zinc and copper, and which are safe for use around children, pets, plants, and even fish. Below are the chemicals we know about, along with some comments on other treatments that are available.

Eco-Friendly Liquid Cleaners

Alkaline/detergent based liquid cleaners work in minutes even when highly diluted. They even clean out mold spores. These are safe for pets, children, garden plants and even fish downstream. A bit of foamy surfactant gives the solution some “sticktoitiveness” and acts as an indicator showing exactly where the solution has been applied. We believe this is the best product for use on composite and tile roofs.

Organic Liquids

An organic solution can be made from citric acid and sodium laurel sulfate( extracted from coconut oil) for a surfactant. This organic product is effective for moss and algae,but it takes longer to work and needs to be applied during a time frame during which there are no active showers, and moderate (preferably dry) weather for a few days after application. If your schedule is flexible and you want the ultimate organic solution, then this option may be for you. Sometimes more than one application is required.

Zinc and other metals

Available in granular form as zinc sulfate, this product is applied either using a broadcast spreader or in white, grainy lines at the top of roof ridges. The idea is that the rain water makes dissolved zinc sulfate and carries it down the roof into bad ole Mr. Moss. Being granular, it is hard to control where the product ultimately goes, but if enough sticks around, the job gets done. As a practical matter most of the granules end up in the gutters or on your lawn.

Zinc, copper and proprietary metallic compounds are also available in liquid form and work when applied according to package directions. You can visit any hardware store and discover the environmental issues with systemic herbicides and metal-based moss control compounds. Just read the warning labels (bring your magnifying glass as it’s all in fine print). Since these generally don’t work any better than environmentally friendlier and less expensive alternatives we don’t understand the attraction.

Zinc Strips

Zinc strips work, just not well enough: The idea is that the rain water reacts with the zinc to produce zinc sulfate which not appreciated by bad ole Mr. Moss. The manufacturers’ rule of thumb is that the strips kill moss for a distance of about four vertical feet for every one and a half inches of vertical exposure on a moderately sloped roof. You can drive around and look at roofs with zinc strips at the top. Usually, those that appear to be working well are installed on roofs that don’t have much of a moss problem in the first place. Typically, you will see them working for two or three vertical feet, with the effectiveness trailing off rapidly. Most people would not like a roof with row after row of zinc strips, but with enough rows installed it would work. Copper works better than zinc, but is prohibitively expensive.

Others

Urban legend has it that powdered Tide laundry detergent is effective against moss. Why Tide? No one seems to know. If you like the idea, try it on your roof. To save money you might try Costco’s Kirkland Laundry Detergent. For some reason, people seem to think that detergent is cheaper but on a per square foot basis it is among the most expensive options. Also, the granules that blow off the roof are very hard on car finishes. Uh oh.

Are there preventative moss treatments?

Some companies sell "moss treatment" as a preventative measure--often for several hundred dollars. The products used are all water soluble and we get nearly 40 inches of rain per year in Oregon--enough to wash away any of them in a matter of weeks if not months. So to us, the notion of "moss treatment" as a preventative measure just doesn't “wash.” Some companies offer multiyear "guarantees" on their "moss treatments." However, there is typically a qualifier involving the need for periodic maintenance, roof cleaning, lack of overhanging foliage, etc. (the fine print).

We examined the idea of offering "moss treatments" with one of these "guarantees." But in the end we can’t (and others can’t) point to any special chemical mechanism or expertise that could honestly justify such a guarantee. So we think these offers present an illusion of quality with no substance, or are just a ploy to sign up repeat service call visits in order to "keep the guarantee in force." As a value proposition, we put these in the same category as car body undercoatings sold at the closing tables of car dealerships. We don’t offer them.

If your roof has a moss problem, then it is a periodic maintenance issue that needn't be expensive, and can be easily managed with a small amount of diligence. There is no "Magic Rescue Remedy" or magical thinking that's going to change it. A look up at the edges of your shingles once in a while will tell you the status of things, and enable you to stay ahead of the moss.