Most roof cleaning quotes will mention either soft washing or pressure washing — and the difference matters more than the words suggest. Pressure washing is cheaper and faster. Soft washing is safer, lasts longer, and is the only method we use on most roof types at AM Property Services. Here's exactly what each one does, where each is appropriate, and why getting this wrong can cost you a re-roof.
What is soft washing?
Soft washing applies a low-pressure spray (usually under 100 psi — about the same as a garden hose) combined with a biocide cleaning solution. The chemistry does the work, not the water pressure. The biocide kills moss, algae, and lichen at the root, which is why a properly soft-washed roof stays cleaner for years rather than weeks.
See our full soft washing guide for the detailed process.
What is pressure washing?
Pressure washing uses high-pressure water (often 2,500–4,000 psi) to physically blast contaminants off the surface. It's the right tool for concrete driveways, brickwork in some cases, and stubborn patio stains. On a roof, that same pressure can lift tiles, strip the protective coating from concrete tiles, force water under tiles into the loft, and damage lead flashing. We cover the full risk picture in our dangers of pressure washing roofs guide.
When pressure washing is appropriate
Pressure washing has its place — just rarely on a roof. We use it for driveway cleaning, patio jet washing, and for some brickwork jobs where the surface can take the force. Done by someone who knows what they're doing, it produces excellent results on the right surfaces.
Why we soft-wash virtually every roof
Three reasons:
Safety for the roof. Concrete tiles have a granular coating that's worth thousands to replace if stripped. Clay tiles can crack. Slate can split.
The clean lasts. Killing moss at the root with biocide stops it growing back for 3–5 years. Blasting it off only removes the visible part — the spores stay and regrow.
Insurance. Most home insurance policies exclude damage caused by pressure washing of roof coverings. If a tile cracks during the job, that's on you.
How to tell which a contractor is using
Ask three questions before booking:
1. What pressure (in psi) do you use on roof tiles? 2. What biocide do you apply, and is it included? 3. Are you insured for damage to roof coverings?
If the answers are vague — or if the price is suspiciously cheap — you're probably looking at a pressure-wash job dressed up as something else. We're happy to answer all three on the phone before you commit. Call 07841 595419 or request a quote online.
