Does roof cleaning help a roof last longer?

The line most often read as a yes is one sentence in the Tile Roofing Industry Alliance's maintenance guide: “Periodic cleaning and resealing can rejuvenate and prolong the surface finish of either cement or clay tile.”

The first condition is the object of the verb. What the sentence says can be prolonged is the surface finish, the face of the tile a person sees, and not the tile body, the underlayment or the roof as a system. The sentences just before it set that scope out. TRI writes that “over time the surface of any product will show signs of aging, including roof tiles”, that slurry-coated tile “can oxidize and turn chalky before gradually wearing down to the concrete base”, and that after this initial change “future erosion occurs at a much slower pace and will never affect the physical properties of the tile.” The chalking TRI describes is a change in the finish, and TRI says in the same passage that the erosion after it never touches the tile's physical properties.

The second condition is the word and. The subject of the sentence is cleaning and resealing together. Cleaning alone is not what it credits, and whether a tile roof needs a sealer at all once it is clean has its own answer in whether a tile roof needs sealing after cleaning.

Read whole, the sentence credits cleaning and resealing, together, with renewing and prolonging a tile's surface finish. It does not say that anything under the finish will last longer.

Two more TRI sentences get lifted as a yes. Each is about something wider than a cleaning, and each names who does the work.

The first reads: “Choosing a professional roofing contractor for repairs and maintenance ensures your safety and the longevity of your roof.” The subject is the choice of a roofing contractor, and the work is repairs and maintenance. It credits that choice of trade for that work, not a cleaning on its own.

The second opens the guide. TRI writes that a tile roof requires regular maintenance to perform optimally, and lists replacing broken tiles, removing algae, mildew and moss, and repairing damaged flashing details as steps “in maintaining its aesthetic and protective qualities for years to come.” Removing growth sits in that list beside a tile replacement and a flashing repair, and two of the three steps are repairs. The protective half of the phrase belongs to the list as a whole.

Nor do the documents credit a cleaning with keeping growth away. TRI says no coating applied on the job site has a long-term preventative effect on the growth, and ARMA says of a bleach and water cleaning on shingle that “The effectiveness of such cleaning is only temporary, and the discoloration may recur.” Those two lines are set out under where a soft wash stops and roofing work begins, and the question of time between cleanings under how long a roof stays clean after a soft wash.

The documents that put cleaning and roof life in the same sentence do it to warn that the wrong method shortens that life.

The Asphalt Roofing Manufacturers Association writes “Never use a pressure washer to clean an asphalt shingle roof”, and gives the reason as granule loss and very likely premature failure of the roof system. GAF's technical bulletin TAB-R-102 says power washing shingles is not recommended because it “may dislodge granules, which can lead to premature shingle failure.” Both warnings are about pressure washing, and both describe a shorter life for shingle, not a longer one. Cleaning shingle without adding to that loss is taken up in whether a shingle roof can be cleaned without losing granules.

The Metal Roofing Alliance puts its cleaning advice in terms of the maker's rules rather than roof life: “Always follow the manufacturer’s specific instructions to help protect and maintain roof warranties.” What that sentence ties to the maker's instructions is the warranty, and it makes no claim about years.

Adding hardware to a roof to keep growth back is not a way around this either. ARMA lists zinc or copper strips among measures that may be employed when it is time to replace a roof, and says adding them to an existing asphalt shingle roof is not recommended because of exposed nails or a broken sealant bond. That argument is made in whether copper strips keep roofs clean.

Florida law adds one more reference point. It concerns what may be represented about a coating on a roof, not what a cleaning does.

Florida Statutes 489.105(3)(e) defines a roofing contractor's trade as covering the installation, maintenance, repair and alteration of all kinds of roofing, waterproofing and coating, “except when coating is not represented to protect, repair, waterproof, stop leaks, or extend the life of the roof.” The word the qualifier governs is coating, and repair is one of its five verbs. A coating represented in any of those five ways is roofing contractor work.

A cleaning is not a coating, so the clause does not reach it. What the clause does show is where Florida puts those five representations: with a coating, inside a roofing contractor's scope. The description this site gives its roof service stays with the look of a roof: a soft wash that removes algae, mold and stains without damaging the roof, and helps protect the look of a home, as set out under what the roof cleaning service says it does. Where cleaning ends and coating or recoating begins is compared in roof cleaning versus roof restoration.

How many years a particular roof has left, and what repair or replacement would change that, is a roofing contractor's assessment.