Of all the pressure washing jobs around a house, how to pressure wash siding is the one where the machine can do damage you will not see for two years. Concrete shows its scars immediately and wood fuzzes up while you watch. Siding just quietly lets water in behind the laps, and the consequences turn up later as mold in the wall cavity. The technique below is built around that single risk.
Quick answer: To pressure wash siding, use 1,300 to 1,600 psi on vinyl with a 40 degree white tip held 2 to 3 feet away. Never spray upward into the laps, because water driven behind the panels ends up inside the wall. Apply a mildewcide detergent from the bottom up, let it dwell, then rinse from the top down keeping the spray angled slightly downward. Cover outlets, lights, and vents, and work in sections you can rinse before the soap dries.
Key takeaways
- Never spray upward. Siding is lapped to shed water downward. Spraying up drives water behind it and into the wall cavity.
- Low pressure, wide tip, far away. 1,300 to 1,600 psi, 40 degree tip, 2 to 3 feet back. Vinyl cracks and dents more easily than people expect.
- Detergent does the cleaning, not force. Mildew is biological. A mildewcide kills it; water just knocks the surface layer off and it grows back in weeks.
- Soap bottom up, rinse top down. Soap applied downward runs over dry siding and streaks; rinse water applied upward gets behind the panels.
- Electricity and water need managing. Cover outlets, fixtures, and the meter, and never wash into a dryer vent or soffit vent.
- Pre 1978 house? The lead rules apply. Pressure washing is allowed, but the wastewater has to be contained.
Why siding is different from concrete or wood
Siding is not a solid surface. It is a set of overlapping panels hung on a wall, deliberately loose so it can expand and contract, and designed on one assumption: water arrives from above and runs down the outside. Rain never gets behind it because rain does not travel upward at 1,500 psi.
Your wand can. Point it up under a lap and you inject water directly into the wall assembly, past the housewrap, into insulation and sheathing that has no way to dry. Nothing looks wrong afterward. That is the problem. The damage shows up later as musty smells, staining from the inside, or mold found during a renovation years on.
So the whole job is: enough pressure to help the soap, never aimed upward, never held close.
What pressure does each type of siding take?
| Siding type | Pressure | Tip | Notes |
|---|---|---|---|
| Vinyl | 1,300 to 1,600 psi | 40 degree white | The common case. Cracks when cold, so avoid washing below 50 F. |
| Aluminum | 1,200 to 1,500 psi | 40 degree white | Dents easily. Oxidised paint will chalk off. |
| Fiber cement | 1,500 psi max | 40 degree white | You are washing a factory coating, not the board. |
| Wood or cedar shake | 500 to 800 psi | 40 degree white | Treat it like decking. Soft wash or brush is better. |
| Stucco | 1,200 to 1,500 psi | 40 degree white | Cracks and hairlines let water straight in. Be careful. |
| Brick | 1,500 to 2,000 psi | 25 or 40 degree | Old lime mortar will wash out. Test first. |
Notice the whole table sits below what a driveway takes. If your machine is a fixed 2,700 psi gas unit with no regulator, back the wand off to 3 or 4 feet, or fit a lower pressure tip. This is why the best pressure washers for vinyl siding tend to be modest electric units rather than the biggest thing on the shelf, and the best pressure washers for house siding are the ones with genuinely adjustable pressure.
The detergent does the work
The grey green film on a shaded north wall is not dirt. It is algae, mildew, and mold, and it is alive. Water at any pressure removes the visible layer and leaves the roots in the surface texture, which is why washed siding often looks great for a month and then goes green again.
A detergent with a mildewcide kills the organism instead of relocating it, which is the difference between a clean that lasts a season and one that lasts a few years. Apply it with the black low pressure soap tip, let it dwell for 5 to 10 minutes, and never let it dry on the surface. The best pressure washer detergents for mold are formulated for exactly this, and for general use the best detergents for a pressure washer cover the siding safe options. A dedicated siding cleaner is worth it on a house with real growth.
One safety rule that matters: never mix bleach based products with anything containing ammonia. The combination produces toxic gas. Read both labels before you put anything in a tank.
How do you pressure wash siding step by step?
- Walk the wall first. Look for cracked panels, loose trim, gaps around windows, and failed caulk. Every one of those is a hole you are about to spray water into. Fix them or avoid them.
- Cover the electrics. Tape plastic over outdoor outlets, light fixtures, the meter, and any open dryer or soffit vent. Water in a vent goes straight indoors.
- Close everything and protect plants. Windows and doors shut, and shrubs at the base wet down and covered before any detergent goes on.
- Wet the plants, then soap from the bottom up. Apply detergent starting low and working upward. Soap running down over dry siding leaves streaks that are surprisingly hard to remove.
- Let it dwell 5 to 10 minutes. Work in sections small enough that you can rinse before it dries, roughly one wall face at a time in shade, less in sun.
- Rinse from the top down. Switch to the 40 degree tip, stand 2 to 3 feet back, and rinse with the spray angled slightly downward, following the direction the siding sheds water.
- Keep the wand level or pointing down. Never up. If you cannot reach the top of a wall without angling upward, you need an extension wand, not a steeper angle.
- Overlap horizontally, move steadily. Work across in bands and keep the wand moving. Holding it still on vinyl can crack a panel.
- Rinse the plants and the ground afterward. Detergent that lands on shrubs needs washing off before it dries.
For anything above one storey, stop and think. Standing on a ladder holding a pressure washer wand is genuinely dangerous, because the wand kicks back when you pull the trigger and you have no way to counter it. Use an extension wand from the ground, or hire it out. The general machine handling rules are in how to use a pressure washer, and if you are doing the whole property, the technique for the flat surfaces is different again in how to pressure wash a driveway.
What if your house was built before 1978?
Homes built before 1978 may have lead based paint, and washing painted siding removes paint whether you intended it or not. That puts the job under the EPA’s Lead Renovation, Repair, and Painting rule when a contractor does it for compensation.
The useful correction here is that washing is not banned. The EPA states plainly that pressure washing is not a prohibited practice under the RRP Rule. What is required is containment: the work area must be isolated so that no dust or debris, including in the waste water, leaves it, and the wastewater has to be disposed of properly, which the EPA suggests discussing with your local water treatment authority.
In practice, for an older painted house: if the paint is chalking or flaking, washing it will spread those chips across your garden and into the storm drain. Test for lead first, and if it is present, hire an RRP certified firm rather than improvising containment yourself.
Common siding washing mistakes
- Spraying upward. The one that causes hidden, expensive damage.
- Standing too close. Vinyl cracks and aluminum dents at distances that feel perfectly reasonable.
- Skipping detergent. The green comes back within a month because you never killed it.
- Soaping top down. Streaks on dry siding that need rewashing.
- Letting soap dry. Permanent looking film. Work smaller sections.
- Washing vinyl in the cold. Below about 50 F vinyl gets brittle and cracks under impact.
- Working off a ladder. The wand kicks and you have nothing to brace against.
- Blasting window seals. Direct high pressure at a window edge forces water past the seal.
If your current machine has one fixed pressure and it is high, that is the real problem to solve. The best pressure washers for cleaning siding put adjustability first, which is exactly the feature this job needs.
Frequently asked questions
What PSI should you use on vinyl siding?
Use 1,300 to 1,600 psi with a 40 degree white tip, held 2 to 3 feet from the wall. Vinyl cracks under concentrated force, especially in cold weather. If your machine has no pressure control, increase your distance instead. Never use a 0 or 15 degree tip on siding.
Can pressure washing damage siding?
Yes, in two ways. Visibly, it cracks vinyl and dents aluminum when held too close. Invisibly and more seriously, spraying upward forces water behind the lapped panels into the wall cavity, where it cannot dry and can cause mold and rot that only shows up years later.
Why should you never spray siding upward?
Siding panels overlap so that water runs down the outside, exactly like roof shingles. Rain never travels upward, so nothing is sealed against it. A pressure washer aimed up under a lap injects water straight past that defence and into the wall assembly. Always keep the spray level or angled slightly down.
Do you soap siding from the top or bottom?
Soap from the bottom up, then rinse from the top down. Detergent applied downward runs over dry siding and leaves streaks that are hard to remove. Rinsing downward follows the direction the panels shed water and avoids driving anything behind the laps.
What kills mold and mildew on siding?
A detergent containing a mildewcide, applied at low pressure and left to dwell 5 to 10 minutes. Mold is a living organism rooted in the surface texture, so plain water only removes the top layer and it regrows within weeks. Never mix bleach based cleaners with anything containing ammonia.
Can you pressure wash a house with lead paint?
Pressure washing is not prohibited under the EPA’s RRP rule, but the work area must be contained so no dust or debris, including in the wastewater, escapes, and the wastewater must be disposed of properly. For pre-1978 homes with flaking paint, test for lead and hire an RRP certified firm rather than improvising containment.
Final thoughts
Washing siding well is a low pressure job that punishes enthusiasm. Let a mildewcide detergent kill the growth, use a 40 degree tip at 1,300 to 1,600 psi from 2 to 3 feet back, soap upward and rinse downward, and never point the wand up under a lap. Get that last rule right and the rest is just patience. If your washer only knows one setting and it is loud, the best pressure washers for vinyl siding are a better starting point than a bigger engine.