PSI, pounds per square inch, is the specification a pressure washer is marketed on and the one that decides least on its own. The number that actually governs a wash is published by whoever made the surface. Vinyl siding manufacturers publish a range. The Brick Industry Association publishes a ceiling. Composite decking manufacturers publish limits that differ from each other by more than a factor of two, and several of them attach the limit to the product warranty.
This guide gives the published figure for every common exterior surface, names the document each figure came from, and gives the date the document was read. Where no manufacturer or trade body publishes a number, this guide says so instead of inventing one. Vinyl siding comes first, because vinyl siding is the surface most readers arrive here about.
What PSI should you use to clean vinyl siding?
Two vinyl siding manufacturers publish the same answer: 1,500 to 2,400 PSI through a 40-degree tip. According to Georgia-Pacific Vinyl Siding, on its Care and Maintenance page read 2026-09-03, the instruction is "Set the pressure using a minimum of 1,500 PSI and maximum of 2,400, using a 40-degree tip." Ply Gem publishes the identical figure on its Siding Care & Maintenance page, read the same day: "Use a 40-degree tip" and "set the pressure between 1,500 and 2,400 PSI."
Both manufacturers put a technique rule ahead of the pressure rule, and both use nearly the same words for it. Georgia-Pacific writes: "When cleaning, hold the power washer straight at eye level. Don't aim the washer upward as the water may collect behind the siding. This collected water could leak, which can produce streaks, or could stay behind the siding, which can cause decay." Ply Gem writes the same instruction and names the same three outcomes: leaks, streaks and decay.
Read that range carefully, because 1,500 PSI is published as a minimum and not as a maximum. Georgia-Pacific is not warning a homeowner away from 1,500 PSI. Georgia-Pacific is saying a machine below that pressure will not do the work, and a machine above 2,400 PSI is outside what the manufacturer will stand behind.
Why do most guides say 1,200 to 1,500 PSI for vinyl siding?
The 1,200 to 1,500 PSI figure repeated across contractor blogs and retailer articles has no siding manufacturer document behind it. The two manufacturer care pages cited above start at 1,500 PSI, which is where the popular range ends. A homeowner following the blog number and a homeowner following the manufacturer number are working roughly 900 PSI apart on the same wall, and only one of the two numbers can be quoted back to a warranty administrator.
Neither number is permission to point a wand upward. The manufacturers spend more of their own word count on spray direction than on pressure, which is a signal about where the failures come from. A vinyl wall assembly sheds water downward through overlapping laps, and an upward jet reverses the one direction the assembly was designed to handle.
Does the vinyl siding trade association publish a PSI figure?
The Polymeric Exterior Products Association, formerly the Vinyl Siding Institute, publishes no PSI figure for vinyl siding at all. According to the association's cleaning page, read 2026-09-03, "Some siding manufacturers do not recommend power washing, while others have limits on the pressure (PSI) and cleaners that can be used", and the reader is told to "Always read the manufacturer's instructions for both the siding and the power washer before you begin."
The association's first recommendation is not a pressure washer at all: "For routine cleaning, a simple rinse with a garden hose is often enough." Where a power washer is used, the association gives the same direction rule the manufacturers give: "Hold the power washer straight at eye level. Do not aim the stream upward, as this can force water behind the siding panels."
The association also publishes a short list of products to keep off vinyl: cleaners with organic solvents, undiluted chlorine bleach, liquid grease remover, nail polish remover, and furniture polish. A trade body declining to publish a pressure number is itself information. The Polymeric Exterior Products Association is saying that the wall in front of you has a brand, that brand has a document, and the document outranks any general rule.
What damages vinyl siding, the pressure or the spray angle?
Water driven behind a lap joint causes the expensive damage, and spray angle is what puts it there. A cracked or warped panel announces itself the same afternoon and costs the price of a panel. Water sitting against sheathing behind intact siding announces itself a year later and costs the price of opening a wall.
Georgia-Pacific and Ply Gem describe that failure in nearly identical language, and the outcome each names is decay rather than breakage. Holding the wand level, working the wall in horizontal passes, and keeping the tip moving does more to prevent the costly failure than dialing the machine down by 300 PSI. A 40-degree tip spreads the same pressure across a wider fan, which is why both manufacturers name the tip alongside the number.
What PSI is safe for fiber cement siding?
James Hardie caps cleaning of its own fiber cement products at under 1,500 psi with a six foot standoff. Technical Bulletin #20, "Cleaning James Hardie Primed and ColorPlus Technology Siding", November 2018, read 2026-09-02, states: "Using wide fan tips that are kept a minimum of 6 feet from the wall and at pressures under 1500 psi will minimize the chance of damaging the siding." The copy read was the one held in Home Depot's product document library, because the manufacturer-hosted PDF did not serve the file on the read date.
The same bulletin attaches money to the instruction: "Damage to siding arising from improper cleaning or maintenance may not be covered by the James Hardie warranty." The bulletin also rules out two methods entirely, stating that sand blasting and acid washing can damage the fiber cement surface and are not recommended.
Six feet is the figure most homeowners miss. Six feet is roughly four to six times the standoff a person working from a ladder naturally holds, and standoff, not the gauge on the machine, is what sets the force actually landing on the board.
What pressure does brick tolerate?
Brick tolerates far less pressure than most people assume, and the Brick Industry Association publishes a hard ceiling. Technical Notes on Brick Construction 20, "Cleaning Brickwork", August 2018 edition, read 2026-09-02, states: "Do not use water pressures higher than 400 psi (2800 kPa) as measured at the nozzle tip unless permitted by brick manufacturer". The same document classifies anything above 800 psi as high pressure and says plainly that "High-pressure water cleaning is not appropriate for brick and may damage the brickwork."
On nozzle and standoff the Brick Industry Association specifies: "Use a 25 to 50 deg. fan-shaped stainless steel nozzle tip, and maintain a distance of 12 in. (305 mm) minimum between the nozzle tip and the brick surface." On proving the method before committing to a wall, the same document requires the operator to "Perform trial cleaning on a 20 sq ft (2 m2) sample area and allow wall to dry before evaluating results".
Mortar is the reason the ceiling sits so low. Brick is harder than the mortar holding it, so a pressure a brick face shrugs off will erode the joint beside it, and the Brick Industry Association names that outcome directly: "excessive pressure may damage brick surfaces, erode mortar joints, and remove finishes or other surface coatings, resulting in a different appearance". Note the distance between 400 psi for brick and 3,000 psi routinely used on a concrete driveway a few feet away.
What pressure does stucco or EIFS tolerate?
Two EIFS manufacturers publish the same ceiling of 500 psi. Sto Corp., headquartered in Atlanta, writes in its StoTherm EIFS Reference Guide, read 2026-09-02: "Do not exceed 500 psi (1.4 MPa) pressure, as the EIFS surface integrity can be destroyed with higher pressure washing." Sika's Senergy technical bulletin, revised February 2024 and read the same day, writes: "Never use water pressure more than 500 psi or allow pressure nozzles to come within 2 feet of the wall."
Sika states the governing principle in one sentence: "The chemicals provide the cleaning, not the water pressure." Sto adds a temperature limit that rules out steam cleaning, because the EPS insulation board inside an EIFS assembly has "a service temperature limit of about 165 deg F (74 deg C)."
Traditional stucco and synthetic stucco both shed water at the surface rather than resisting water driven into a crack under pressure, which is why the published ceiling for EIFS is one eighth of what a driveway takes. Confirm which cladding is on the wall before choosing a pressure, because an EIFS wall and a fiber cement wall look similar from the street and differ by 1,000 psi in what the manufacturer allows.
What PSI works on concrete and concrete pavers?
Concrete pavers have a published pressure band, and poured concrete flatwork does not. According to the Concrete Masonry and Hardscapes Association, in document PAV-TEC-005-22 read 2026-08-31: "A high pressure sprayer applies cleaner and water between 1,000 and 4,000 psi (6.9 and 27.6 MPa), and at a rate between 2 and 6 gallons/minute (7.6 and 22.7 liters/minute)." The same document warns about the joints rather than the paver face: "A low angle of attack from a wide nozzle spray will also reduce the risk of dislodging joint sand."
That band is published for interlocking concrete pavement, and restating it as a limit for a poured slab would misuse the source. No trade association or manufacturer document in this guide publishes a pressure ceiling for poured concrete driveways and sidewalks, so the honest answer for a slab is a method rather than a number: begin wide and far, test an area nobody looks at, and move closer only if the test area demands it.
Three concrete conditions justify backing the pressure down regardless. Spalling or already crumbling concrete loses more material under a jet that sound concrete ignores. Exposed aggregate loses the paste around the stone before it loses the stone. Decorative stamped and colored concrete carries a surface treatment, and stripping that treatment converts a cleaning job into a resealing job. For an ordinary sound slab, driveway cleaning is closer to a flow problem than a pressure problem, which the next section explains.
What PSI is safe for a wood deck?
Thompson's WaterSeal publishes 1,200 to 1,500 PSI for a wood deck and treats the machine as a rinse tool rather than a cleaning tool. Answering the question "Should I use a power washer to clean my deck?" in its FAQ, read 2026-09-03, the manufacturer writes: "If you do choose to use a power washer, begin with the ready-to-use cleaner, and use the power washer for extra rinsing muscle, keeping it at 1,200-1,500 PSI."
The same answer names the failure mode in the manufacturer's own words: "You can cause 'feathering,' which is a fuzzy-looking surface. You can even 'carve' into the wood if the pressure is extreme." Feathered wood is not only cosmetic damage. Raised grain absorbs stain unevenly and shortens the life of the coating applied over it, which is why the guidance comes from a coating manufacturer in the first place.
Treat that figure as what it is: surface preparation guidance from a company selling the coating, not a species-by-species standard. No wood trade association publishes a PSI ceiling by species that this guide was able to verify. Work along the grain rather than across it, keep the wand moving, and remember that on wood the cleaner does the work while the water carries the residue away.
What PSI can composite decking take?
Composite decking has no single answer, and two major manufacturers disagree by more than a factor of two. Trex allows, in its Care Guide read 2026-09-03, "A pressure washer with no greater than 3100 psi that has a fan attachment/adjustment and soap dispenser", and requires "a fan tip no closer than 8 in. (203 mm) from the decking surface". TimberTech, in its Care & Cleaning Guide read the same day, allows a "maximum pressure of 1,500 psi", limits the machine to "rinsing only", and requires spray "in the direction of the grain pattern, never across the grain or width of the board".
Both manufacturers attach the limit to the warranty rather than to appearance. Trex writes: "Use of a pressure washer greater than 3100 psi could damage the boards and void the warranty." Trex splits its guidance further by product generation, stating that "Trex does not recommend the use of a pressure washer on early-generation Trex decking" and that using one "will void the warranty".
So the first question on a composite deck is not what PSI. The first question is which board, and the second is which generation of that board. A number carried over from one brand to another has no standing with either manufacturer, and on a composite deck the warranty is the thing being risked. Deck cleaning starts with identifying the product, and a homeowner who cannot identify it should default to the lower published figure.
Can an asphalt shingle roof be pressure washed?
No. The Asphalt Roofing Manufacturers Association is explicit: "Never use a pressure washer to clean an asphalt shingle roof as this will cause granule loss and very likely premature failure of the roof system." That sentence appears in "Algae & Moss Prevention and Cleaning for Asphalt Roofing Systems", published February 22, 2012 and read 2026-09-03.
ARMA prescribes chemistry in place of pressure. The association's stated method is "a 50:50 mix of laundry strength liquid chlorine bleach and water", applied with a sprayer and allowed "to dwell on the roof surface for 15 to 20 minutes", after which the operator is told to "rinse thoroughly with low pressure water".
ARMA publishes no psi number for that rinse, so nobody should attach one to ARMA. The instruction that matters is the prohibition: granules are the layer protecting the asphalt mat from ultraviolet light, and once a jet removes them the roof ages faster for the rest of its life. Roof cleaning on asphalt shingles is a chemistry job with a rinse, which is the definition of a soft wash.
Which nozzle color corresponds to which spray angle?
Generac publishes the color code shipped with its own pressure washers, and the same convention appears across most of the consumer market. According to Generac's help center article "What Do the Different Colored Nozzles Do on My Pressure Washer?", read 2026-09-03, the tips run as follows.
| Color | Spray angle | Generac's stated use |
|---|---|---|
| Red | 0 degrees | Paint removal, oil stains, rust removal, or other stubborn substances |
| Yellow | 15 degrees | Removing stains on hard porous surfaces such as concrete driveways |
| Green | 25 degrees | All purpose: home siding, brick patios, wood, decks, driveways and sidewalks |
| White | 40 degrees | Gentle cleaning of cars, trucks, boats, RVs, patio furniture, lawn equipment |
| Black | Low pressure, detergent only | Combining water with cleaning agents |
Generac's own article lists the green 25-degree tip as suitable for "home siding, brick patios, wood, decks, driveways and sidewalks", and that recommendation is looser than what the cladding manufacturers publish. Georgia-Pacific and Ply Gem both specify a 40-degree tip on vinyl. The Brick Industry Association specifies a 25 to 50 degree fan tip held at least 12 inches away on brick. Where a machine maker and a cladding maker disagree, the cladding maker governs the wall, because the cladding maker is the party writing the warranty.
Note also that the color code is a manufacturer convention rather than an ANSI or ISO standard. Calling it a standard overstates it. Check the tips that shipped with the machine in front of you rather than assuming a chart found online describes them.
Why does GPM matter as much as PSI?
GPM, gallons per minute, decides how fast a surface finishes, while PSI decides how hard the water lands. The Concrete Masonry and Hardscapes Association publishes both numbers in the same sentence, "between 1,000 and 4,000 psi ... and at a rate between 2 and 6 gallons/minute", because the pair describes the tool and neither figure describes it alone.
Pressure loosens material and volume carries it away. A machine with high pressure and low flow cleans a narrow strip slowly, and slow progress tempts an operator to close the standoff distance to speed the work up. Closing the standoff is where surface damage starts, on every material in this guide. More flow at moderate pressure finishes a large flat surface faster and leaves less evidence that anyone was there.
This is the practical difference between a consumer machine and a contractor machine, and the difference is flow rather than pressure. Two machines rated at the same PSI clean at different speeds when one moves twice the water, and the slower one is the one more likely to leave wand marks.
How far should the nozzle sit from the surface?
More of these manufacturers publish a standoff distance than publish a pressure, and the distances differ as widely as the pressures do. James Hardie requires a minimum of 6 feet on fiber cement. The Brick Industry Association requires a minimum of 12 inches on brick. Sika prohibits bringing a nozzle within 2 feet of an EIFS wall. Trex requires a fan tip no closer than 8 inches from a composite deck board.
Every one of those four figures is a minimum rather than a target, which means the safe direction is always farther away. Standoff is also the only control available to someone who cannot change the machine: a fixed-pressure washer becomes gentler by stepping back, and no purchase is required.
Work the test area at the published distance first. If the test area comes clean at 12 inches, nothing is gained by moving to 6 inches, and a great deal can be lost.
What is inside a professional exterior wash, and what sits outside it?
Inside the scope of a wash from Thrare Contracting: identifying the cladding and, where a brand is identifiable, working to that manufacturer's published limit; a test area on an inconspicuous elevation before the visible ones; protection of landscaping, light fixtures, outlets and openings; detergent applied and rinsed according to the product label; wash water managed so nothing enters a storm drain; and a walk of the finished work with whoever owns the building.
Outside the scope, and quoted separately if wanted: repointing eroded mortar joints, replacing cracked or warped panels, caulk and flashing repair, painting, staining or sealing, and any repair a wash uncovers. A wash exposes conditions that were already there, and a wash does not fix them. The Brick Industry Association's own instruction to inspect and repair before cleaning exists for that reason.
Also outside the scope: any surface the owner cannot identify and the manufacturer cannot be traced for, where the published limit is unknown and the warranty risk sits with the owner rather than with the contractor. In that case Thrare Contracting works to the lowest published figure that plausibly applies, and says so in writing before starting.
What does a contractor need from you before the first wash?
- The cladding type, and the brand if a label, an invoice or a builder record survives.
- The age of the exterior, and whether any previous wash left marks, streaking or panel damage.
- A working water source, and confirmation of who pays for the water.
- The location of storm drains, downspout outlets and any landscape or planting to be protected.
- Access to every elevation, and any parking or gate arrangement needed to reach them.
- Whether any surface sits under a manufacturer warranty that names a cleaning method, because that document sets the limit rather than any general rule.
Where is the wash water allowed to go?
Wash water from exterior cleaning is a non-stormwater discharge, and under 40 CFR 122.26 a discharge to a municipal separate storm sewer system that is not composed entirely of stormwater is an illicit discharge unless an NPDES permit authorizes it. EPA's NPDES Stormwater Program page, read 2026-08-31, sets out that framework. The practical compliance route is containment: water that never reaches a storm drain or a surface water needs no permit.
The Brick Industry Association states the same rule in a trade document rather than a regulation: "Some jurisdictions may require containment and treatment of the runoff water before it can leave the site. Dilution of runoff and its release into the stormwater management system should not be expected or allowed unless expressly permitted by the applicable jurisdiction." Sto Corp. and Sika both close their cleaning procedures by telling the reader to check local regulatory requirements for disposal of wash water and cleaning solutions.
Cleaning chemistry is regulated on a separate track. Under 7 U.S.C. 136j(a)(2)(G) it is an unlawful act "to use any registered pesticide in a manner inconsistent with its labeling", and EPA defines antimicrobial pesticides as "substances or mixtures of substances used to destroy or suppress the growth of harmful microorganisms such as bacteria, viruses, or fungi on inanimate objects and surfaces." A soft wash product carrying an antimicrobial claim is governed by its registered label, and that label sets the dilution and the dwell time rather than a contractor's habit. ARMA's 50:50 bleach ratio is ARMA's stated method for shingles and never overrides a product label.
Quick reference: what each manufacturer or trade body publishes
| Surface | Published figure | Who published it |
|---|---|---|
| Vinyl siding | 1,500 to 2,400 PSI, 40-degree tip, held level | Georgia-Pacific Vinyl Siding and Ply Gem, read 2026-09-03 |
| Vinyl siding, association view | No figure published; follow the manufacturer | Polymeric Exterior Products Association, read 2026-09-03 |
| Fiber cement siding | Under 1,500 psi, wide fan tip, 6 feet minimum standoff | James Hardie Technical Bulletin #20, read 2026-09-02 |
| Brick and mortar | 400 psi maximum at the nozzle tip, 25 to 50 degree fan, 12 inches minimum | Brick Industry Association Technical Notes 20, read 2026-09-02 |
| EIFS and acrylic stucco | 500 psi maximum, 2 feet minimum standoff, no steam | Sto Corp. and Sika Senergy, read 2026-09-02 |
| Interlocking concrete pavers | 1,000 to 4,000 psi at 2 to 6 gallons per minute, wide spray | Concrete Masonry and Hardscapes Association PAV-TEC-005-22, read 2026-08-31 |
| Poured concrete flatwork | No published trade ceiling located; test an inconspicuous area | No source found as of 2026-09-03 |
| Wood deck | 1,200 to 1,500 PSI, rinse only, after a cleaner | Thompson's WaterSeal FAQ, read 2026-09-03 |
| Composite decking, Trex | 3,100 psi maximum, fan tip no closer than 8 inches | Trex Care Guide, read 2026-09-03 |
| Composite decking, TimberTech | 1,500 psi maximum, fan tip, rinsing only, along the grain | TimberTech Care & Cleaning Guide, read 2026-09-03 |
| Asphalt shingle roof | Never pressure wash; 50:50 bleach, 15 to 20 minute dwell, low pressure rinse | Asphalt Roofing Manufacturers Association, 2012 bulletin, read 2026-09-03 |
Read across that table and one pattern stands out: the published limits span 400 psi to 4,000 psi, a factor of ten, across surfaces that sit within a few feet of each other on the same building. A single machine setting cannot serve a brick wall, a vinyl elevation and the driveway in front of them. Related reading: cleaning vinyl siding without damage, pressure washing compared with soft washing, and soft washing in Atlanta.
Thrare Contracting works to the published figure for the surface in front of the crew, and names the document when a property manager or homeowner asks which one. To discuss a specific building, schedule service online, call (678) 748-3578, or read what a full house washing or pressure washing visit covers.