Pressure Washing in Washington: Moss, Mildew & When You Need a Pro
Pressure Washing in Washington: Moss, Mildew & When You Need a Pro
Fighting the Pacific Northwest's never-ending battle with green growth
Why Pressure Washing Matters in Washington
If you live in Washington—especially west of the Cascades—you know the deal: moss on the roof, mildew on the siding, green algae on the driveway, and black streaks on everything. Our wet climate creates ideal growing conditions for organic buildup that doesn't just look bad—it can damage your home.
Regular pressure washing isn't optional here; it's essential maintenance. This guide covers what needs washing, how often, DIY considerations, and when to call a professional.
Pressure Washing Costs in Washington (2024)
Common Services
| Service | Average Cost | Cost Range |
|---|---|---|
| House siding (1,500–2,500 sq ft) | $300–$500 | $200–$800 |
| Driveway (2-car) | $150–$250 | $100–$400 |
| Patio/deck | $150–$300 | $100–$500 |
| Roof cleaning (soft wash) | $350–$600 | $250–$1,000 |
| Fence (both sides) | $200–$400 | $150–$600 |
| Concrete walkways | $100–$200 | $75–$300 |
| Full property package | $500–$900 | $400–$1,500 |
Cost Per Square Foot
| Surface | Price Range |
|---|---|
| Siding (soft wash) | $0.15–$0.35/sq ft |
| Concrete (driveway, patio) | $0.15–$0.30/sq ft |
| Deck | $0.30–$0.50/sq ft |
| Roof (soft wash) | $0.20–$0.50/sq ft |
| Fence | $0.50–$1.50/linear ft |
What Affects Price
| Factor | Cost Impact |
|---|---|
| Heavy moss/mildew buildup | +20–40% |
| Multi-story home | +25–50% |
| Steep lot/difficult access | +15–30% |
| Delicate surfaces (cedar, old paint) | +15–25% |
| Soft wash chemical treatment | +10–20% |
| Stain/seal application after | +$2–$5/sq ft |
What Needs Pressure Washing (And How Often)
Recommended Schedule for Western WA
| Surface | Frequency | Why |
|---|---|---|
| House siding | Every 1–2 years | Mildew, algae, dirt |
| Driveway/concrete | Every 1–2 years | Moss, oil stains, algae |
| Deck | Annually (before staining) | Moss, mildew, gray weathering |
| Roof | Every 2–3 years | Moss removal, longevity |
| Fence | Every 2–3 years | Moss, mildew, weathering |
| Gutters (exterior) | Every 1–2 years | Black streaks, oxidation |
Eastern Washington
Less frequent washing needed due to drier climate:
- Siding: Every 2–3 years
- Driveways: Every 2–4 years
- Decks: Every 2–3 years
- Roofs: As needed (less moss growth)
Moss and Mildew: The PNW Problem
Understanding the Growth
| Growth Type | Appearance | Where It Thrives |
|---|---|---|
| Moss | Green, fuzzy, cushion-like | Roofs, north-facing surfaces, shade |
| Algae | Green film or streaks | Concrete, siding, shaded areas |
| Mildew | Black or gray spots | Siding, trim, humid areas |
| Lichen | Crusty patches | Roofs, concrete, wood |
Why It's a Problem
- Roofs: Moss lifts shingles, holds moisture, causes rot
- Siding: Mildew stains, can penetrate paint
- Concrete: Moss creates slip hazards
- Decks: Accelerates wood decay
- Curb appeal: Looks neglected
Prevention After Cleaning
| Surface | Prevention Method |
|---|---|
| Roof | Zinc or copper strips at ridge line |
| Siding | Trim overhanging trees, improve airflow |
| Concrete | Apply sealer, improve drainage |
| Deck | Annual cleaning, stain/seal |
| Fence | Improve sun exposure if possible |
Pressure Washing vs Soft Washing
Pressure Washing
What it is: High-pressure water (1,500–4,000 PSI) to blast away dirt and growth.
Best for:
- Concrete (driveways, patios, sidewalks)
- Brick and stone
- Heavily soiled hard surfaces
- Paint prep on durable surfaces
Not for:
- Asphalt shingles (damages roof)
- Cedar siding (gouges wood)
- Old/peeling paint (makes it worse)
- Vinyl siding at wrong angle (water intrusion)
Soft Washing
What it is: Low-pressure water (500 PSI or less) combined with cleaning solutions that kill growth.
Best for:
- Roof cleaning
- Cedar and wood siding
- Painted surfaces
- Vinyl and aluminum siding
- Delicate surfaces
Why it works: Chemicals do the cleaning, not pressure. Kills moss and mildew at the root so they don't return as quickly.
Which Method for What
| Surface | Method | PSI Range |
|---|---|---|
| Roof | Soft wash only | 40–100 |
| Cedar siding | Soft wash | 200–500 |
| Vinyl siding | Soft wash or low pressure | 500–1,200 |
| Painted siding | Soft wash | 500–1,000 |
| Fiber cement (Hardie) | Low–medium pressure | 1,000–1,500 |
| Concrete | Pressure wash | 2,500–3,500 |
| Brick | Medium pressure | 1,500–2,500 |
| Deck (prep for stain) | Low–medium | 500–1,500 |
DIY vs Professional
DIY Makes Sense When:
- Concrete driveway or patio only
- Small areas (under 500 sq ft)
- You own or can rent proper equipment
- No delicate surfaces involved
- You understand PSI requirements
- Not working at heights
DIY Costs
| Item | Cost |
|---|---|
| Pressure washer rental (day) | $50–$100 |
| Surface cleaner attachment | $25–$50 |
| Cleaning solution | $20–$50 |
| Safety gear (goggles, etc.) | $20–$40 |
| Total DIY | $115–$240 |
| Pro cost (same driveway) | $150–$300 |
Why Hire a Pro
- Proper equipment – Commercial machines, surface cleaners
- Knowledge – Right pressure for each surface
- Soft wash capability – Chemical application systems
- Height access – Ladders, lifts for multi-story
- Insurance – If something gets damaged
- Efficiency – What takes you 4 hours takes them 1
Common DIY Mistakes
| Mistake | Consequence |
|---|---|
| Too much pressure on siding | Gouged wood, water behind siding |
| Pressure washing roof | Granule loss, shortened shingle life |
| Holding nozzle too close | Etched concrete, damaged surfaces |
| Wrong angle on vinyl | Water driven behind siding |
| Skipping cleaning solution | Growth returns quickly |
| Power washing painted surfaces | Paint stripped, bare wood exposed |
Prep for Other Work
Pressure washing is often step one for larger projects:
Before Exterior Painting
- Timing: 2–3 dry days before painting
- Purpose: Remove mildew, loose paint, dirt
- Method: Soft wash or low pressure
- Critical: Surface must fully dry before paint
Before Deck Staining
- Timing: 48–72 hours before staining
- Purpose: Remove gray wood fibers, mildew, old stain
- Method: Low pressure (500–1,200 PSI for cedar)
- Follow up: Brightener if wood is gray
Before Sealing Concrete
- Timing: 24–48 hours before sealing
- Purpose: Open pores for sealer penetration
- Method: Full pressure (2,500–3,500 PSI)
- Note: Must be completely dry
Lead Paint Considerations
Pre-1978 Homes
Pressure washing pre-1978 painted surfaces can release lead paint particles:
| Risk | How to Mitigate |
|---|---|
| Lead chips in soil | Contain runoff, cover plantings |
| Lead dust in air | Avoid high-pressure scrubbing |
| Contaminated water | Don't let it enter storm drains |
Best Practices
- Test paint before aggressive washing
- Use soft wash methods on old paint
- Hire professionals for heavy lead paint situations
- Consider EPA RRP requirements if significant paint removal
Seasonal Timing
Best Times to Pressure Wash
| Service | Best Timing | Why |
|---|---|---|
| Siding | Spring (Mar–May) | After winter grime, before algae season |
| Driveway | Spring or fall | After leaf/debris season |
| Deck | Late spring | Before summer use, staining season |
| Roof | Late spring | After moss winter growth peak |
| Pre-painting | Summer | Dry weather for painting |
When to Avoid
- During rain – Obviously
- Below 50°F – Water can freeze, chemicals less effective
- High wind – Spray goes everywhere
- Direct hot sun – Cleaning solution dries before rinsing
Questions to Ask Pressure Washing Contractors
- What method do you use? (pressure vs soft wash)
- What PSI for my surfaces?
- What cleaning solutions do you use?
- Are your chemicals safe for plants/pets?
- Do you have liability insurance?
- How do you protect windows and landscaping?
- What's included in the price?
- Do you offer any guarantees?
- How long until I can use the surfaces?
- Can you show recent before/after photos?
Red Flags
- One pressure setting for everything
- No discussion of soft washing for delicate surfaces
- Pressure washing asphalt roofs
- No insurance
- Significantly below market pricing
- Can't explain their process
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Related Resources
- Exterior Painting in Seattle
- Deck Staining in WA
- Roof Leak Repair in Seattle
- Siding Installation in WA
Last updated: 2024. Prices reflect Washington market rates. Get multiple quotes for your specific project.