Siding

Pressure or soft washing

CertainTeed says it does not recommend power washing vinyl or polymer siding, because it can cause moisture intrusion, damage or discoloration. It suggests a house-wash attachment that connects to your garden hose instead¹.

The siding industry’s trade group is a little more permissive. It says a power washer can be used with caution, and notes that some manufacturers don’t recommend it while others set a pressure limit². James Hardie tells fiber cement owners to skip the high-pressure washer and use a low-pressure hose with a soft, medium-bristle brush that isn’t metal³.

That makes soft washing the sensible default: put the cleaner on at low pressure, scrub only where it needs it, and rinse gently.

Nozzle and pressure

None of these care guides gives a pressure figure that applies to all siding, so we don’t print one. Your siding maker’s care guide is the place to look for a limit.

If you do use a power washer, hold it straight at eye level and don’t aim the stream upward, which can force water behind the panels². CertainTeed also warns against prolonged or high-pressure rinsing of open ventilated areas¹. Kärcher lists its widest 40 degree tip for more delicate surfaces⁴.

Cleaners to use and avoid

Protect plants and keep runoff out of drains

Cleaning chemicals can damage plants and grass. The Brick Industry Association’s advice holds for any surface: protect nearby plants, and where needed keep the cleaning solution and runoff off plants and the soil around them⁵. Soaking beds with plain water before and after, and covering what you can, is the practical version of that.

Street drains are not sewers. EPA reminds people that storm drains lead directly to local waterways, not to treatment facilities. Its tips for washing outdoors: use biodegradable, phosphate-free, water-based detergents, use as little as you can, wash on a driveway or yard rather than in the street, and send the wash water onto grass or gravel⁶. In Greene County, polluted runoff that enters the storm sewers is often discharged into local rivers and streams without treatment⁷, and Beavercreek asks residents not to dump anything down a storm sewer or drain⁸.

If you see suds, a rainbow sheen or an odd color in a ditch, stream or storm drain, Greene County asks you to report it to the County Engineer’s Office at 937-562-7500⁹.

Common damage

• Forced water behind sidingSpray aimed upward can push water up under the laps and behind the panels².
• Moisture and discolorationCertainTeed names moisture intrusion, damage and discoloration as the reasons it advises against power washing¹.
• A scratched finishMetal brushes and abrasive sponges can damage the finish on fiber cement siding and trim³.

When not to pressure wash at all

Step by step

1. Read the care guideFind your siding maker’s cleaning instructions and any pressure limit before you start.
2. Close up the houseShut windows and doors on the wall you are washing, and take care around windows, doors, electrical wiring and plumbing².
3. Protect the bedsSoak plants near the wall with plain water and cover any you can.
4. Apply the cleaner from the bottom upUse mild soap and water, or the maker’s mildew mix, with a soft brush or a hose-end house-wash attachment. Start at the bottom and work up to prevent streaking².
5. Rinse level or downwardRinse with the garden hose, keeping the stream level or pointed down so water doesn’t get behind the laps.
6. Rinse the plants againGive the beds another drink of plain water when you finish.

Before you start, read the safety page. If the job looks bigger than you want to take on, DIY or hire lays out what each way involves.