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Is it Good to Pressure Wash Your Roof?

Maintaining your roof may be one of the most important aspects of homeownership. After all, it is the first line of defense against damaging UV rays and faces direct exposure to forces of nature such as rain, hail, and snow. As such, it is essential that your roof is properly maintained, with cleanings recommended at least every other year.

Is it good to pressure wash your roof? Yes, it can be good to pressure wash your roof, depending on the type of roof you have. However, pressure washing roofs must be done with the proper settings and techniques in order to avoid doing expensive damage to your roof.

There are many different types of roofs covering buildings across the nation, just as there are many different types of pressure washers with a variety of settings. It is important to know the composition of your roof and what type of cleaning it requires prior to attempting to perform a pressure wash.

Is Pressure Washing Your Roof Safe?

Cleaning your roof is obviously an important component of owning a home, but it is not very convenient. It can be time-consuming, not to mention potentially dangerous, to be crawling on your hands and knees and scrubbing down a roof when your cleaning materials want to slide away every time you reach for them.

Would it not be easier to just get a pressure washer and quickly spray the entire roof down?

Pressure washing your roof can be safe, but the proper settings and techniques must be employed prior to starting a pressure wash on your roof.

When looking into how to effectively use a pressure washer to clean your roof, there are a number of different considerations that need to be taken into account. In general, regardless of the type of roof you are trying to clean, the following settings and techniques should be followed during the pressure washing process:

  • Roof composition
  • PSI settings of your pressure washer
  • Nozzle capabilities
  • Direction of wash
  • Additives included

Roof Composition

This is the first place you need to start when deciding how to pressure wash your roof.

Roofs can be made from a variety of materials, each of which is capable of fulfilling a specific function. However, unique types of roofs will have varying abilities to be able to withstand a pressure wash.

The following are some of the most common types of roof materials:

  • Concrete – this is an extremely durable type of roof, often found in apartment buildings or industrial complexes where the roof will be used for foot traffic or other purposes. These roofs are largely flat and capable of handling a wide array of pressure washer settings.
  • Metal – most metal roofs are made of some kind of tin alloy and are another durable roofing option found largely atop of barns, shops, and other stand-alone work facilities. Like concrete, metal roofs are capable of handling numerous pressure washer settings.
  • Clay tile – these roofs are found atop a wide range of residential properties. They make for a particularly strong choice in warmer climates, as the clay helps insulate from the heat and prevent molding rot due to the growth of algae. While durable, any roof made from tile needs to be pressure washed with a little extra caution.
  • Asphalt shingle – this is arguably the most common type of roof found in housing developments and. Asphalt shingles offer a variety of benefits that include ease of installation, color matching, sound insulation, and fire resistance, all at an affordable price. However, these roofs need to be monitored very closely during a pressure wash.
  • Wood shake – these roofs offer superior insulation and are very aesthetically pleasing, especially for houses and cabins found in wooded areas that want to match with the natural backdrop. Like asphalt shingles, though, these roofs must be pressure washed with extreme caution.
  • Slate – slate roofs are extremely fire and mold resistant. They also absorb very little water, helping them last longer in winter conditions where freezing and cracking are prevalent. The downside is that slate is easily damaged by forceful contact, making pressure washing a risky proposition.

PSI Settings of Your Pressure Washer

While knowing the composition of your roof is the most important aspect prior to undertaking a pressure wash, knowing your pressure washer’s PSI settings is a close second.

PSI, or pounds per square inch, is a measure of the pressure of the water as it is released from your pressure washer. The higher the PSI of the pressure washer, the more force the water has as it contacts the surface. 

A common PSI rating for a pressure washer is 2,600. Considering that a football is inflated to about 15 PSI and a car tire is inflated to about 32 PSI, it is easy to see how much force a pressure washer can exert when given an open throttle.

Luckily, the vast majority of pressure washers come with an adjustable gauge that allows the user to adjust the PSI output, providing an appropriate strength of water flow for specific tasks. In the event that your pressure washer does not have an adjustable gauge, adapters can be purchased that can be attached to your water outlet, performing the same function.

You can quickly clean the more durable roofs, such as concrete and metal, at higher PSI settings, while asphalt and slate shingles should be scaled back to very low PSI, or perhaps no PSI at all.

Nozzle Capabilities

Pressure washers come with a variety of nozzles. Some nozzles shoot straight jets of water, while others fan out to cover a wider target.

At the same PSI settings, the straight jet nozzles will provide a more forceful impact than will the nozzles that fan the water out. Therefore, you will want to use jet nozzles to break up areas of tough grime while employing fanned nozzles to quickly sweep away softer, looser debris.

Concrete and metal roofs will be able to handle the impact from straight jet nozzles, while all other types of roof should stick to fanned nozzle types unless the PSI is completely restricted on the pressure washer.

Direction of Wash

If you plan on using a pressure washer to clean your roof, you must always work from the top of your roof and down toward the gutter. While it is tempting to simply climb up a ladder and spray from the gutter up, doing so puts you at risk of getting under your shingles or tiles and lifting them from the surface of the roof, leading to leaks down the road.

In order to successfully perform this “downward wash,” the following steps should be taken:

  • Use rubber-soled shoes – you will need shoes with good traction if you plan on being up on the roof for a pressure wash. In addition, make sure that you are keeping your feet a strong and safe distance apart and only planting your feet on dry areas of the roof, allowing previously washed areas to dry before advancing.
  • Obtain adequate hose length – once on the roof, you do not want to have to come down until the job is finished. Therefore, prior to starting the wash, make sure that you have enough hose length to reach all corners of the roof.
  • Start small – focus on a small area of roof, such as one or two shingles or tiles, prior to starting the widespread wash. This will allow you to compare the washed area to surrounding areas and make note of its effectiveness.
  • Keep your distance – even at low PSI settings with wide fanning nozzles, the less durable roofing materials may suffer damage if you spray them from too close. As such, start with the nozzle about 18 inches away from the roof and slowly move it closer until it gains effectiveness, ideally getting no closer than 12 inches away from the roof’s surface.
  • Check frequently – as you wash, take note of whether any shreds of asphalt are being forced loose or if there are any noticeable signs of wear on the slate. Frequently check in the gutters to see if there is any roofing material mixed with the dirt and debris being washed away.

By successfully employing these “downward wash” techniques to pressure wash your roof, you will have a clean roof and a gutter full of debris. The gutters can be easily cleaned by pressure washing all of the material through the system.

If you are pressure washing a concrete roof, the roof is likely to be flat with a gradual taper toward a center drainage grate. If this is the case, work from the outside in, until all debris has been drained or trapped by the grate.

Additives Included

Most pressure washers will come with settings that allow for soap and/or chemicals to be sprayed with the pressurized water. This is important for a couple of reasons.

First, some chemicals may not mix well with your particular roof type. For example, if your roof is made of wood slate, you will want to check before spraying to make sure that any additives you include will not cause wood to deteriorate prematurely.

Second, for roofs that cannot withstand high pressure, two rounds of washing may be necessary. You may need to do a round of washing in which soap and/or chemicals are used to break down the accumulation of tough grime, followed by a round of washing in which all debris is rinsed away.

Is Pressure Washing Your Roof Bad?

Pressure washing your roof is not bad. In fact, pressure washing your roof can be a highly effective means of administering the regular cleanings that are required to keep your roof strong over the course of its life.

However, given the diverse types of roofs and the many pressure washer settings available, it is not a simple “yes” or “no” answer. Let’s look at the different roof types and decide the best way to pressure wash them.

Concrete Roofs

Concrete roofs are the most durable roofs imaginable. They will be able to withstand high-pressure impact, any nozzle setting, and will not have their integrity tested by soaps or chemicals. As such, you are free to use your pressure washer however you see fit when cleaning concrete roofs.

There are a couple of things you will want to consider before starting your pressure wash, though. 

  • As concrete roofs are generally flat to allow for rooftop traffic, the drainage will not be as fast as for the more slanted roofs. So, if you are using any particularly sticky cleaning additives, make sure the roof is thoroughly rinsed to avoid a slippery after-wash surface.
  • There are also likely to be tables and chairs located on most concrete roofs. Using high PSI settings will cause debris to ricochet and splatter on other objects. So, you may need to consider pressure washing other rooftop items after washing the roof, or simply keep the pressure washer at settings where this splatter is not as significant of an issue.

Metal Roofs

It is arguable that metal roofs are the easiest to clean with a pressure washer. As they are extremely durable, basically any PSI or nozzle setting can be used. The one thing you will need to watch for, though, is that you do not include any additives known to make metal oxidize.

Metal roofs are also the one type of roof where it may not be best to employ the “downward wash” technique. As the vast majority of metal roofs do not come in tiles or shingles, but, rather, large panels, there is not the threat of uprooting them when spraying from the gutter up.

This is important because metal roofs can get very slippery when wet, so you may not want to be on them while employing a downward wash. Because they are slippery when wet, any loose debris will likely flow back into the gutter with the water, making an upward washing technique all the more feasible.

Clay Tile

Clay tile roofs are a solid choice to be pressure washed. As with any roofing material that comes in small pieces, you will always want to use a downward wash and minimize the PSI, ideally at a maximum of 30-50 PSI.

If you go above this PSI and try to use a narrow jet nozzle, there is a small chance you could cause a clay tile to shatter upon contact. However, if you are keeping the PSI in the recommended range and using a downward wash, it should be safe to use any nozzle type when pressure washing your clay tile roof.

Asphalt Shingle

You must be very careful when using a pressure washer to clean a roof made of asphalt shingles. As these shingles are coated in small particles that are capable of being knocked away under direct force, the following guidelines should be followed when pressure washing a roof made of asphalt shingles:

  • Always use the downward wash technique to keep the shingles from getting uplifted
  • Keep your pressure washer at no more than 30 PSI, possibly turning the PSI completely off and doing a regular hose pressure clean if you detect any damage from the pressurized stream
  • Never use the direct jet nozzles, sticking to the fan options, ideally with a fanned stream of at least 25°
  • Make the soap and/or chemical additive the main factor in breaking down the buildup on the shingles, and not the pressurized water

Wood Shake

The process for cleaning wood shake roofs with a pressure washer is very similar to that for cleaning clay tiles.

The difference is that wood shake tiles are slightly less durable than clay tiles, so you will want the PSI at no more than 30 while avoiding using direct jet nozzles in favor of fanned options.

Slate

The process for cleaning slate roofs with a pressure washer is nearly identical to that for cleaning asphalt shingles. This roofing material is highly susceptible to having ruts washed into under direct force, so avoid all direct jet nozzles and keep the PSI at a maximum of 30

Be sure to follow all appropriate downward wash techniques, specifically in terms of keeping the nozzle tip a safe distance away from the roof’s surface and checking early and often for any signs of damage caused by the pressure wash.

Is it Good to Pressure Wash Your Roof: The Final Verdict

Yes, it is good to pressure wash your roof.

However, unlike with other surfaces where you can quickly and forcefully wash away grime, you need to be a little more circumspect when attempting to pressure wash your roof. If done incorrectly, cleaning the roof can be offset by the structural damage caused by the water pressure.

As such, it is imperative to have a thorough understanding of your roof composition and use the proper pressure washing settings and techniques before you attempt to use your pressure washer to quickly and efficiently wash your rooftop grime into the gutter. 

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