Although roofs are built to last for decades, proper maintenance is a task homeowners should perform regularly. A well-maintained roof lasts longer, and it keeps the market value of a house or a building at its prime. A clean roof also improves energy efficiency and makes your home look more aesthetically pleasing.
The average cost to clean a roof is $414, though you might pay anywhere between $299 and $566 for the project.
Cleaning Methods by Roof Type
Roofs are available in various types of materials; thus, the cleaning solutions used on them differ according to the type of roof you have and the kind of issues you need to address. Among the most common types of roofing materials, both the methods and solutions used vary quite a bit and are important to note when calculating costs.
The most common roof material used, regardless of a home's location, is asphalt roof shingles. These shingles are notable for their granular, sand-like finish, which is designed to wear slowly over time. Because of the delicate, layered nature of these shingles, it is incredibly important to be gentle when cleaning them so as not to inadvertently destroy a layer of protection and reduce the lifespan of your roof. For this reason, low pressure-washing of no more than 30 psi, equal to that of a garden sprayer, is recommended.
Asphalt Cleaning Solutions
Because asphalt shingles are the most popular type of roofing material, there is no shortage of advice and DIY internet recipes for cleaning them. The most popular recipe includes chlorine bleach, water, and trisodium phosphate (TSP). However, there are several dangers associated with this combination, including the fact that bleach only kills the surface layer of mold and algae, opening it to regrowth. Furthermore, it poisons the vegetation underneath the roof and corrodes metal fastenings. Another common product, sodium hydroxide (lye), is safer for plants but toxic to humans and similarly corrosive.
For this reason, a specially formulated asphalt roof cleaner is the safest and most effective solution to use. Many non-corrosive and environmentally friendly products exist on the market, including some proprietary blends specific to roof cleaning companies as well as DIY cleaners available at most local hardware stores.
Ceramic tile roofs are popular in Spanish-style homes as well as in the Southwest and subtropical regions of the United States. They are also the only common roofing material type that can withstand higher-pressure washing techniques without suffering unnecessary corrosion or wear. However, if you are using a pressure washer, it is still important to closely control the psi because applying high pressure in the wrong place can crack ceramic tile, requiring replacement. A low-pressure "soft" wash is therefore the recommended method.
Because of the environmental dangers of a bleach-based cleaning system, using a specialized formula to clean a ceramic tile roof is the safest and most effective choice. Look for a low-pressure formula designed to both lift out stains and attack mold, fungi, and algae growth.
Clay tile has a similar look to ceramic tile and is popular in California as well as other Southwest and Southern states. Made using a specialized method that combines clay and sand to form tiles, clay roofs are excellent insulators that help reduce cooling costs. However, their production method results in a more porous tile than ceramic roofs, making them subject to wear even under low-pressure washing. Therefore, they should be cleaned using a garden sprayer, similarly to asphalt shingle roofs, or a diverted low-pressure washer, which simply sprays water over the tiles to help wash away dirt.
Although tile-specific cleaners work on clay tile roofs, properly maintained clay roofs should have a protective coating or sealant that inhibits the growth of many common organisms. While cleaning clay tile is still necessary, harsh chemicals or complex solutions are not. Instead, just use plain water or water mixed with mild dish detergent.
Concrete tiles are more popular in rainy, temperate climates such as the Pacific Northwest and outside of the U.S. in similar places, most specifically in the United Kingdom. They are distinct because they combine features of standard tile with asphalt, consisting of a porous concrete base brushed with a sandy surface designed to wear off over time. Due to their construction and likely location, most people choose to clean concrete tile roofs because of moss buildup. However, the delicate nature of concrete tiles and their wearable sandy finish mean that any sort of pressure washing can damage the concrete tiles, shortening the lifespan of the roof.
If the goal is to remove moss, most experts recommend a physical scraping and/or brushing of dry moss using nothing more than a 9-inch trowel and hand brush. Afterwards, applying chemicals such as zinc sulfate or other proprietary blends designed to inhibit moss growth can protect the roof for up to three years.
Slate is more common on upscale and luxury homes and notable for its extended lifetime of 75-200 years. However, because it is made of natural material, its maintenance requirements are slightly different. Because of the natural origin of slate tiles, they are extremely delicate and often do not lie flat atop one another. For this reason, the use of any kind of pressure washing is not recommended. Slate roofs are also subject to delamination, making the use of any sort of harsh chemical very dangerous and impacting the durability and lifespan of the roof tiles.
To clean a slate roof properly, it is necessary to be gentle in both the approach and the solution. Start by hand, physically gathering any debris or moss. Alternately, a rubber or vinyl leaf rake is a handy tool, especially for reaching up the slope and under tiles. For more stubborn spots and growth areas, a mixture of water and mild dish soap applied with a medium-stiff hand brush and then rinsed with a gentle hose spray is acceptable.
You can get a rough idea of the cost based on the size and slope of your roof. The larger and more complex the roof design, the more costly it will be to clean. Gross square footage and gutters will also factor in. The height of your roof may incur an additional cost. For example, if your home is three stories high, it takes a bit more work to get the professionals and equipment up there. Also if your roof is very steep, you might be charged extra for the professionals to get up there and stay safely on top of it.
Where you live will directly affect the cost of cleaning your roof. If you live somewhere that your roof may be exposed to the elements, such as the beach or where it snows and sleets frequently, your professional may need to spend a little more time cleaning your roof to get all of the dirt, mold and grime off.
Cleaning off moss and algae is important. Large trees that produce lots of shade on a roof can foster the growth of moss and algae. High moisture levels brought about by rain can cause moss to accumulate on the roof and block your gutters. These dark stains on a roof act as a sponge to absorb the sun's heat, which causes higher air conditioning bills. Moss is of great concern as it can shorten the lifespan of untreated wood and asphalt roofing materials. The thick moss growth keeps the roofing materials damp for extended periods of time, promotes wood rot, and erodes the asphalt in shingles. The more moss and algae present, the more expensive the cost of cleaning may be.