Clean your exterior walls.

Whether you are preparing to sell your home or simply performing routine maintenance, a deep clean removes years of atmospheric soot and organic growth. This guide covers the methods, costs, and regulations involved in professional exterior house cleaning in the UK.

What Does the Work Involve?

• Site Assessment: A professional will inspect the substrate (brick, K-Rend, stone) to determine the safest cleaning method and identify any pre-existing damage.
• Protection: Covering delicate plants, outdoor furniture, and electrical points with tarpaulins or tape to prevent chemical or water damage.
• Debris Removal: Manually scraping away heavy moss from roofs or plinths and clearing gutters to ensure proper drainage during the wash.
• Softwashing: Applying low-pressure chemical solutions (biocides or sodium hypochlorite) to kill organic spores on delicate surfaces like modern render.
• Pressure Washing: Using high-pressure water for hard-wearing surfaces like block paving, concrete driveways, and certain types of old brickwork.
• Steam Cleaning (DOFF/ThermaTech): Using superheated water at low pressure to remove paint, wax, or biological matter without damaging fragile masonry.
• Rinsing and Neutralising: Thoroughly washing down all surfaces to remove chemical residues and ensuring windows are cleaned of any overspray.

Typical Costs

Prices for exterior cleaning vary significantly based on the size of the property, the height of the building, and the level of staining. Most reputable UK firms include VAT in their quotes, but always double-check this during the estimation phase.

The primary cost drivers are access requirements and the type of cleaning agent used. Properties with "K-Rend" or "Monocouche" render require specialised softwashing chemicals, which are more expensive than standard detergents but prevent the substrate from cracking under high pressure.

How Long Does It Take?

• Small Terraced House: 3–5 hours for a front and back wall wash.
• 3-Bedroom Semi-Detached: 1 full day for a comprehensive clean including driveway and gutters.
• Large Detached Property: 2–3 days, especially if roof cleaning or multiple treatments are required.
• Drying and Sealing: If applying a water-repellent seal or re-sanding a driveway, an additional dry day is usually necessary between cleaning and finishing.

DIY or Professional?

While many homeowners own a domestic pressure washer, using it incorrectly can cause thousands of pounds in damage. High pressure can "strip" the face off old bricks, blow holes in modern render, and force water into the wall cavity, leading to internal damp.

Expert Tip: Never use a high-pressure washer on K-Rend or Monocouche render. It can leave permanent "wand marks" and invalidate your render manufacturer's warranty.

Professionals have access to industrial-grade biocides that kill the root systems of moss and algae, preventing rapid regrowth. They also possess the safety equipment required for working at height, which is a major risk for DIYers using ladders and heavy hoses.

Choosing the Right Tradesperson

Exterior cleaning is an unregulated industry, meaning anyone can buy a pressure washer and call themselves a specialist. To ensure a quality job, follow these steps:

• Check Insurance: Ensure they have Public Liability Insurance (minimum £2 million) that specifically covers "damage to the item being worked upon."
• Ask About Methods: A good pro should explain why they are choosing softwashing over pressure washing for your specific wall type.
• Review Portfolios: Look for before-and-after photos of similar properties, particularly those with the same type of render or stone.
• Water Source: Confirm if they need access to your external tap or if they bring their own water bowser (common for rural areas).

Questions to ask:

• "What chemicals will you be using, and are they safe for my pets and garden plants?"
• "How do you handle wastewater run-off to ensure it doesn't enter protected drains?"
• "Do you provide a guarantee against the return of algae for a specific period?"

UK Regulations

• Work at Height Regulations (2005): Tradespeople must plan work at height properly and use the correct equipment (scaffolding, towers, or MEWPs) to prevent falls.
• COSHH: Professionals must manage the Control of Substances Hazardous to Health when using strong biocides or acidic cleaners.
• Water Industry Act 1991: In some regions, professionals must have a standpipe licence if they are drawing large volumes of water from the mains.
• Environmental Agency Guidelines: It is illegal to allow certain cleaning chemicals to enter surface water drains. Professionals should use "bunding" or drain covers to manage run-off.

Common Problems

• Blown Render: If water is forced behind a small crack at high pressure, it can cause large sections of render to detach from the wall.
• Efflorescence: Cleaning can sometimes trigger "salt damp" or white powdery marks on bricks as the wall dries out; a professional can treat this with specific acids.
• Plant Die-back: Strong bleach-based cleaners can kill lawns and shrubs if they are not thoroughly pre-soaked with fresh water and rinsed.
• Window Seal Damage: Excessive pressure around window frames can perish rubber seals or blow the "mist" seal in double glazing.
• Streaking: If chemicals are applied unevenly or in direct sunlight, they can leave permanent "run marks" on the property exterior.

Frequently Asked Questions