TL;DR
Apply detergent from the bottom up and rinse from the top down. Soap running over dry surface leaves a streak that is difficult to remove, while rinse water running over already-cleaned surface simply redeposits soil. Getting this one order right eliminates most of the streaking people blame on their detergent.
The rule in one sentence
Soap goes up, water comes down.
Applying from the bottom of a wall upward means every drip lands on a surface that is already wet with the same solution. Rinsing from the top downward means dirty runoff always crosses surfaces you have not finished yet, so nothing clean gets re-soiled.
Reverse either direction and you get the two classic failures: vertical soap streaks that show after everything dries, and a band of dirty residue along the bottom of an otherwise clean wall.
Why bottom-up application prevents streaks
A detergent hitting dry, dusty siding immediately starts working in a thin line where it ran. That line cleans faster than the surface around it, so once everything is rinsed you see a permanent-looking stripe.
If the surface below is already wet with solution, a run has nothing to bite into. It blends.
There is a second reason. Detergent that dries on a surface stops cleaning and starts leaving residue. Working bottom up keeps the lower portion wet the longest, which is exactly where drips and runs concentrate.
Do not confuse this with the direction of the wand itself. On siding, the stream is always angled downward regardless of which part of the wall you are working, because water driven upward gets behind the panels. Application moves up the wall in bands; the spray still points down.
Why top-down rinsing is the only sensible order
Gravity decides where the dirty water goes, so the rinse has to start where the runoff will fall from.
Rinse the top course first and everything below gets a preview wash. Rinse the bottom first and the top rinse simply dumps soil back over it, forcing you to do the bottom twice.
Top-down also handles the surfaces you cannot avoid draining onto: window sills, trim ledges, the top of the foundation, and any horizontal surface that collects runoff. Finish those last and they end clean.
On a two-story wall, work in overlapping horizontal bands from the top and let each band flow into the next. Keep the surface below wet so the runoff never dries and marks.
The full sequence for a house exterior
- Prep. Close windows and doors, cover or disconnect exterior electrical fixtures, and move furniture and grills away from the walls.
- Pre-wet plants. Soak shrubs, beds, and grass with plain water and keep them wet through the job.
- Pre-rinse the wall, top down. A light rinse knocks off loose dust and cobwebs, and wetting the surface stops the detergent from soaking in unevenly.
- Apply detergent, bottom up. Work in sections you can come back to before they dry. On a downstream machine this means fitting the low pressure soap tip, as covered in how detergent injection works.
- Let it dwell. Five to ten minutes, never to dryness. Mist with plain water if a section starts drying.
- Rinse, top down. Wide tip, downward angle, steady distance, overlapping passes.
- Rinse the surroundings. Plants, walkways, and the driveway get a final flush so nothing dries on them.
- Do flat surfaces last. Walkways, patios, and the driveway collect everything that came off the house, so they are the end of the job, not the start.
Source: exterior cleaning contractor practice guidance
Where the order changes
Roofing. A roof is a soft wash job for a professional, never a pressure job, and it is handled before the walls so runoff lands on siding you have not yet cleaned. Homeowners should not be on a roof for this.
Gutters and soffits. Wash the outside of gutters and the soffit area before the wall below, for the same runoff reason. Soffits need a downward-angled spray because their vents are openings into the attic, which is the point made in cleaning soffits and fascia without water intrusion.
Decks and porches attached to the house. Do the wall first, the deck second, so wall runoff lands on a surface you are about to clean anyway.
Windows. Save glass for last and clean it by hand. Pressure past a window seal is how a double-pane unit ends up permanently fogged.
Section size and working in the sun
The practical limit on section size is drying time, not reach.
In cool, shaded conditions you might apply detergent to an entire elevation before rinsing. In direct sun on a hot afternoon you may only manage ten or fifteen feet of wall before the first part starts to dry.
Follow the shade around the house through the day, or start early. A surface that dries with detergent on it will streak no matter how carefully you applied it.
Never work a wand from a ladder to reach a high band. Use an extension wand from the ground, or hire the upper elevations out. The recoil on a ladder is a genuine fall hazard, and no cleaning result is worth it.
Siding deserves one extra caution
Siding is a shedding system. Each course overlaps the one below so water runs down the face, and none of it is sealed against water pushed upward.
That is why every part of this sequence keeps the stream angled downward and the pressure low, and why the whole job is really a soft wash rather than a pressure wash. The reasoning is in soft washing and when it applies, and the step-by-step is in washing vinyl siding without forcing water behind it.
If you are using a bleach-based house wash, never combine it with an acidic cleaner such as a rust remover or masonry etcher. That combination releases chlorine gas. Finish one product, rinse thoroughly, then move on.
FAQ
Do you pressure wash a house top down or bottom up?
Apply detergent from the bottom up and rinse from the top down. Soap running over dry surface leaves streaks, while rinse water running over finished surface redeposits soil. The spray itself stays angled downward on siding in both stages, because water driven upward gets behind the panels.
Why does my siding look streaky after washing?
Usually because detergent was applied top down, or because a section dried before it was rinsed. Both leave lines where the solution worked longer than the surrounding surface. Work in smaller sections, out of direct sun, and mist with plain water if anything starts to dry.
What order should I wash the outside of a house in?
Roof first if it is being treated at all and by a professional, then gutters and soffits, then walls by elevation, then attached decks and porches, then walkways and the driveway last. Windows are cleaned by hand at the end. Flat surfaces collect everything, so they finish the job.
Should I wet the house before applying detergent?
Yes. A light top-down pre-rinse removes loose dust and cobwebs and, more importantly, wets the surface so the detergent spreads evenly instead of soaking into dry patches. It also shortens how long the solution needs to dwell.
Can I wash a house in direct sunlight?
You can, but it is harder. Heat evaporates the detergent before it has time to work and dries residue onto the surface, which causes streaking. Follow the shade around the house through the day, work smaller sections, and keep a plain water mist handy.
Order, dwell time, and spray angle decide how an exterior wash looks when it dries. Our pressure washing service sequences the whole property so nothing gets cleaned twice or missed. Get a quote and we will walk it with you.