House Washing & Roof Cleaning Scope Guide

Soft washing siding and roofs vs pressure washing.

High-pressure water cleans concrete, but on vinyl siding, stucco, painted wood, and asphalt roof shingles it can force water behind lap joints, etch oxidation stripes, or strip ceramic roof granules. A clear exterior washing quote states which surfaces get low-pressure soft washing and which get mechanical surface cleaning.

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How soft washing and pressure washing divide by surface

Use these four surface rules when writing your job description or checking a contractor's bid.

Vinyl, fiber cement & painted wood siding

Method: Low-pressure soft wash (under 100-300 PSI at the wall)

A downstream injector or dedicated 12V/air pump applies a diluted sodium hypochlorite and surfactant solution to kill green algae and black mildew spores.
After 5 to 10 minutes of dwell time, the wall is rinsed with high-volume, low-pressure water so nothing is forced under lap siding or window weep holes.
Ask the contractor to check for chalky oxidation on older vinyl or aluminum siding first; disturbing oxidation unevenly leaves wand stripes.

Stucco, EIFS & painted brick

Method: Soft wash with two-step dwell and gentle rinse

Textured stucco and synthetic EIFS crack or pit easily under high-pressure fan tips.
Organic staining in stucco pores responds better to a stronger soft-wash mix and a second application than to raising nozzle pressure.
Elastomeric paint on stucco should be rinsed gently to avoid peeling blistered spots.

Asphalt shingle, tile & metal roofs

Method: Dedicated roof soft-wash pump (no pressure washer wand)

Black roof streaks are caused by Gloeocapsa magma bacteria feeding on shingle limestone filler.
Roof Manufacturers (ARMA) specify low-pressure chemical treatment applied at garden-hose pressure rather than high-pressure washing or rotary surface cleaners.
Downspouts and foundation beds must be pre-wetted and continuously diluted while roof solution drains off.

Plant, window & fixture protection

What the quote should state in writing:

Pre-soaking all turf, shrubs, and flower beds with fresh water before applying house-wash or roof-wash solution, and post-rinsing leaves afterward.
Taping keyhole locks, doorbell cameras, and exterior GFCI outlets so wash water does not trip breakers.
Rinsing window glass after siding mix dries so surfactant spots do not bake in the sun.

Related pressure washing scope guides

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