When considering alternatives to remove the ugly looing mold or dirt from your roof shingles, tiles or metal roof, pressure cleaning is a good alternative to consider. This can come in handy especially if you have the right kind of roof, and if the conditions are conducive for using the pressure washers. All you need is a step by step guide on how to go about this task.

There are several variations that need to be observed when pressure washing a roof, but a compromise can be struck on what would for most types of roofs.

General Step By step guide for Pressure Cleaning a roof

The following items would be required for pressure washing a roof

  • A pressure washer. You can get an electrical powered or a gas powered pressure washer, although most of the portable once are gas powered and are easy to move around.
  • A ladder is required for climbing the roof.
  • Flowing water supply into the washer preferably from a tap through a garden hose.
  • Safety equipment especially non slip shoes.


  1. As a safety concern for using gas powered machines, examine the pressure washer to confirm that it is safe for operation and there are no obvious dangers. This include checking for oil or gas leaks or broken parts that might need replacement.
  2. Connect the water pressure nozzle to the washer. Care must be taken to use the correct type of nozzle as the nozzle produce different kind of water jets that might not be effective for pressure washing. Some washers are shipped with a single nozzle that can be adjusted to produce different kinds of jets.
  3. Clean the inlet nozzle filter of the washer before connecting the water inlet hose. This is to ensure uninterrupted water flow into the pressure washer.
  4. Find a suitable place to position your pressure washer. This point should be stable enough to support the machine, and be in a position such that the entire roof can be accessed from that point. In some cases, you might need to get a longer washer pipe.
  5. After properly positioning the washer, open the water supply to run water through the machine. This ensures that all gas and air particles in the machine are eliminated before starting the engine.
  6. Start the engine by pulling the cord. Different machines might have different methods of starting but most gas powered types have an ignition cord.
  7. Climb the roof and position yourself strategically to avoid slipping and falling down. Wet roofs tend to be very slippery.
  8. Aim the nozzle at the roof and squeeze the trigger to release the high pressure water on the dirt. You need to start from the top of the roof coming down to avoid the dirty water running over cleaned surfaces.

It is unnecessary to use a detergent when pressure cleaning a roof since the high pressure water takes care of most of the dirt. However, if you must use one to remove some stubborn stain, the detergent is applied on the roof before spraying begins. Most detergents are not suitable for using inside the pressure washer.

Different types of roof might require different washing techniques as pressure water can damage some of the roof shingles. This is especially when cleaning tiles or asphalt roofs. Care must be taken to avoid causing damage to these types of roofs.

Pressure washing Roof Shingles

Pressure washing of roof shingles may not be necessary especially in case when the roof has normal dirt and leaves. This is because the pressurized water might remove the protective coating of grit on the shingles shortening their lifespan. It can however be considered as an option for removing chronic dirt such as mold, algae or moss.

The following is a step by step guide for pressure washing roof shingles:

  1. Connect the correct type of nozzle to the washer. The recommended type of nozzle is the 35-degree spray wand that is less likely to damage the protective layer of grit from the shingles.
  2. Connect your water supply to the washer using the inlet valve. You can use specialized cleaning solutions that specializes in removing mold if the mold is more chronic. Moss should however be easy to remove using plain water.
  3. Position your ladder at an appropriate place that allows you to access most of the roof surface. Care must be taken not to lean the ladder on the roof shingles as the ladder might break them.
  4. Climb the ladder with the pressure hose in hand and position yourself at a point closest to the top of the roof. Cleaning with pressure starts from top coming down.
  5. Turn on the pressure washer with minimum pressure and slowly increase the pressure as you point the nozzle towards the shingles until you attain the pressure where the dirt is easily removed.
  6. move across the roof with the washing wand adjusting the pressure as needed. In case some mold doesn’t come off easily, moving the nozzle closer to the shingle might help. Keep your eyes on the shingles to observe any signs of particles peeling away with the water. If this happens, you need to reduce the pressure of the water.

While on the roof, care must be taken while moving over the roof to avoid falling. This include avoiding unnecessary movement, and sticking to moving along reinforced lines. In case you need to turn around, ensure to lift your feet one at a time to avoid disorienting the singles.

Pressure washing Roof Tiles

Tiles can also be comfortably cleaned with the pressure washer. Tiles are prone to damage from pressure water than shingles hence the process is expected to be smooth and trouble free. Extra care should however be given to safety as tiles get really slippery when they are wet. It is important to have the right kind of shoes with soft anti-skid soles.

You need to be cautious while moving on the roof to avoid falling. It is advisable to step along the joining lines of the tiles as they are the areas with the strongest support. It is important to avoid the wet areas of the roof all the same as you move around. Stick to the dry area as much as possible

Use a ladder to get to the top of the roof but the ladder must not be positioned in a way as to press against the tiles to avoid breaking the tiles. It is important to have someone hold the ladder for you as you climb to help prevent accidents from falling.

The pressure washer has to be set on a low pressure value with low psi as you start cleaning. Cleaning is best done in a horizontal manner as you start from one side of the roof, say the left side and work your way to the right side.

Spraying direction is down from the ridge towards the gutters to ensure the dirt and debris do not flow to the cleaned surfaces. Detergents can be applied to the tiles according to your needs and the kind of dirt but not to the pressure washer itself.

Pressure Washing Metal Roofs

Metal roofs are the most ideal for pressure washing. They have smooth surface and are less prone to damage from pressure water. Movement is easier along the reinforced columns of the roof provided one has the correct anti-skid shoes to avoid slipping.

The following tips can be implemented in pressure washing a metal roof

  • Apply detergent to the roof before spraying with water to make it easier for the dirt and stain to dissolve.
  • Connect a 35-degree nozzle to the pressure washer or a 40-degree nozzle. The 35-degree nozzle is used for the case of thick layers of dirt and debris on the roof. It cleans more efficiently but it takes more time. If the roof has a lot of dirt use the 35-degree nozzle.
  • Using warm water makes it easy to clean as the warm water easily dissolves the dirt and stains.
  • Roofs with gentle slopes are easier to clean since they provide a leeway for walking easily on the roof.  Roofs with steep slopes might be dangerous to work on with a pressure washer and is recommended to use chemical cleaning methods on such roofs.

Pressure washing alternatives can be used to clean roofs that have a variety of dirt and debris including algae moss and mold. One might employ this technique when they are not comfortable with using chemicals or bleach to clean the roof.

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