Pressure washing a roof
| Pressure washing a roof | |
| Type | Roof cleaning method |
|---|---|
| Pressure | High |
| Agent | Water |
| Result | Immediate and visible |
| Defined by | Trade practice; no statute or standard |
Pressure washing removes growth from a roof mechanically, with a high-pressure water jet. It is the method that produces the most dramatic immediate result and the one that carries the most risk to the covering. No statute or published standard defines the method, so the description here is of established trade practice and carries no citation for the technique itself. What is regulated is the surrounding activity: the work is work at height,[1] and any biocidal product applied must be authorised for that use.[2]
What it does well[edit]
It removes bulk, fast, and the result is visible on the day. On a robust covering in sound condition, with an operator controlling pressure and distance, it clears moss and much lichen in a single visit where a chemical treatment would take a season.
That immediacy is why it is asked for, and it is a real advantage rather than only a presentational one where a property is being sold or handed over.
What it costs the covering[edit]
The pressure that removes lichen from a surface is close to the pressure that removes the surface. On a concrete tile the applied finish is what protects the body from absorbing water,[3] and stripping it accelerates the weathering that made the roof look tired in the first place. On clay, the fired surface is formed in manufacture and cannot be restored.[4] On slate, material removed is a large proportion of a thin unit.
There is also water where water should not be. A jet directed up a lap drives water under the covering, and a roof that leaks for the first time shortly after being pressure washed is a common sequence.
Access[edit]
Pressure washing generally requires the operative on the roof, which sits lower in the hierarchy the Work at Height Regulations set out than methods that can be carried out from a platform or the ground.[1] On an older roof, foot traffic is itself a cause of cracked tiles and dislodged slates, and damage found afterwards is frequently attributed to the water when the cause was the access.
See also
References
- abThe Work at Height Regulations 2005. legislation.gov.uk. Retrieved 2026-09-05
- ^Regulation (EU) No 528/2012 concerning the making available on the market and use of biocidal products. legislation.gov.uk. Retrieved 2026-09-05
- ^BS EN 490: Concrete roofing tiles and fittings. Product specifications. BSI. Retrieved 2026-09-05
- ^BS EN 1304:2013: Clay roofing tiles and fittings. Product definitions and specifications. BSI. Retrieved 2026-09-05