Hiring the right retaining wall contractor is the difference between a lifetime investment and a multi-thousand-dollar failure. In Washington State, where glacial till and heavy rainfall are standard, a retaining wall isn’t just a decorative garden border—it is a critical piece of engineering designed to hold back tons of earth and manage water runoff.
The main question homeowners often have is: “How do I know if this contractor actually knows how to build a structural wall?”
The answer lies in their technical knowledge of drainage, soil pressure, and local codes. If they focus more on the “look” of the blocks than the aggregate behind them, you should keep looking.
This guide provides the seven critical questions you must ask to vet a provider, ensuring your wall stands for decades, not just a single season.
1. Are You Licensed, Bonded, and Specially Insured for Structural Hardscaping?
In Washington, a general contractor’s license is a baseline requirement, but it is not enough. You need to verify that they are specifically bonded and insured for the type of excavation and structural work required for retaining walls.
Why Licensing Matters
A license proves the contractor is registered with the state and has a basic level of accountability. However, “hardscaping” often falls into a gray area. Ensure their insurance covers property damage specifically related to earth movement and excavation.
The Liability Gap
If a contractor hits a utility line or if the wall collapses and damages a neighbor’s property, their insurance is the only thing standing between you and a massive lawsuit. Ask for a certificate of insurance (COI) sent directly from their agent to you.
2. How Do You Plan to Manage Hydrostatic Pressure and Drainage?
Water is the primary cause of retaining wall failure. When rain saturates the soil behind a wall, it creates “hydrostatic pressure”—thousands of pounds of force pushing against the back of your structure.
The Drainage Checklist
A qualified retaining wall contractor should immediately mention these three components:
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Perforated Drain Pipe: A “weep” system or a perforated pipe at the base of the wall to carry water away to an outlet.
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Clean Aggregate Backfill: At least 12 inches of crushed, clean gravel (not dirt) directly behind the wall to allow water to drop straight to the pipe.
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Filter Fabric: A geotextile layer that prevents fine soil particles from clogging the drainage gravel.
If a contractor says “the water will just seep through the cracks,” they are describing a future failure. Without a dedicated drainage system, water will eventually cause retaining wall cracks or a complete blowout.
3. What is Your Process for Sub-Grade Preparation and Compaction?
What happens beneath the ground is more important than the blocks you see on top. A wall is only as stable as the soil it sits on.
The Leveling Pad
The contractor must excavate a trench and install a leveling pad of compacted gravel. The first course of your wall should be partially buried (usually 1 inch of burial for every 1 foot of wall height). This prevents the “toe” of the wall from kicking out under pressure.
Mechanical Compaction
Ask what equipment they use. They should be using a vibratory plate compactor for every “lift” (layer) of soil and gravel backfill. Manual tamping is insufficient for structural integrity. Proper compaction ensures the wall doesn’t settle or lean over time.
4. Will This Project Require Engineering or a Permit?
In many Washington cities, including Seattle and Lynnwood, a permit is required for any wall over 4 feet tall. However, this is not a hard rule.
When You Need a Professional
You likely need an engineer and a permit if:
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The wall is over 4 feet high.
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The wall is supporting a “surcharge” (a driveway, a house, or a steep slope above it).
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You are building in a “Critical Area” (like a steep slope or near a shoreline).
A reputable contractor should be able to tell you if your project in Lynnwood or surrounding areas requires a permit and should have a relationship with a structural engineer to provide the necessary stamps.
5. Which Material Approach Do You Recommend for My Specific Slope?
Different slopes and soil types require different material solutions. A one-size-fits-all approach is a red flag.
Comparing Options
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Segmental Concrete Blocks: Best for heights under 6 feet and tight curves. They are fast to install and have a high durability rating.
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Natural Stone Rockeries: Often used in the PNW to handle massive slopes. They require heavy machinery to place. Knowing how to move large rocks and boulders safely is a specialized skill.
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Timber/Wood: A railroad tie retaining wall is often the most budget-friendly but has the shortest lifespan (15–20 years).
Ask the contractor why they chose a specific material for your yard. Their answer should be based on soil pressure and drainage, not just aesthetics.
6. What is the Total Estimated Timeline and Construction Impact?
A retaining wall project is invasive. You need to know how long your property will be a construction zone and what the “collateral damage” will be.
Access and Equipment
Large projects require excavators and skid steers. Ask the following:
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Will my driveway be blocked?
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How will you protect the lawn from machine tracks?
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Where will the tons of excavated dirt go?
A standard residential project usually takes 3–7 days of active labor, but this can extend to weeks if there are unforeseen soil issues or permit delays.
7. What Does the Warranty Specifically Cover?
Many contractors offer a “tailgate warranty”—meaning the warranty ends as soon as their truck leaves your driveway. You need a written agreement.
Workmanship vs. Materials
The manufacturer of the blocks may have a lifetime warranty on the stone itself, but that won’t help you if the wall leans because of poor compaction. You want a workmanship warranty (typically 3–5 years) that covers settling, leaning, or drainage failure.
A contractor who stands by their work won’t hesitate to put these terms in writing.
Common Misconceptions About Hiring
“The lowest bid is the best value.”
In retaining wall construction, the lowest bid usually means corners were cut in the one place you can’t see: the drainage and compaction. Rebuilding a failed wall costs 2x more than doing it right the first time. Check our guide on retaining wall costs in Seattle to get a realistic baseline for pricing.
“I can just do it myself over a weekend.”
A garden border is a DIY project. A 4-foot structural wall holding back a hill is a liability. Without the correct mechanical compaction and laser-leveling, DIY walls often fail within the first three rainy seasons.
FAQs Homeowners Are Afraid to Ask
Will the heavy equipment break my underground pipes? A professional contractor will have the “Call Before You Dig” (811) service mark your lines. However, they should also discuss how they plan to navigate around sensitive areas like septic fields or old sewer lines.
Why is there so much gravel in my yard during the build? That gravel is the “drainage column.” It is arguably the most expensive and important part of the wall. If you don’t see piles of clean 3/4″ crushed rock, your wall is being built incorrectly.
Can I build my wall right on the property line? This depends on your local municipality. Usually, the wall and its footing must be entirely within your property. Building on a line often requires a recorded easement or a signed agreement with your neighbor.
When This Solution is NOT a Good Fit
A retaining wall might not be the right choice if:
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Massive Landslides: If the entire hillside is moving, a wall is just a Band-Aid. You may need deep-seated soil stabilization or “soil nailing.”
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Budget Constraints: If you cannot afford the proper drainage and engineering, it is better to wait. A poorly built wall is a safety hazard.
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Strict Zoning: In some protected wetlands or ECAs (Environmentally Critical Areas), the city may prohibit the “cut and fill” required for a wall.
INTERNAL LINKING RECOMMENDATIONS
Anchor Text: retaining wall contractor Suggested Page Topic: Retaining Wall Service Page Where to Place the Link: In Section 2, under “The Drainage Checklist.”
Anchor Text: retaining wall cracks Suggested Page Topic: Repair/Maintenance Blog Where to Place the Link: In Section 2, discussing hydrostatic pressure.
Anchor Text: Lynnwood Suggested Page Topic: Lynnwood Service Location Page Where to Place the Link: In Section 4, discussing permitting requirements.
Anchor Text: how to move large rocks and boulders Suggested Page Topic: Informational Rock Handling Guide Where to Place the Link: In Section 5, under the “Natural Stone Rockeries” bullet point.
Anchor Text: railroad tie retaining wall Suggested Page Topic: Timber/Wood Material Guide Where to Place the Link: In Section 5, under the “Timber/Wood” bullet point.
Anchor Text: retaining wall costs in Seattle Suggested Page Topic: Comprehensive Pricing Guide Where to Place the Link: In the “Common Misconceptions” section.
Anchor Text: English garden Suggested Page Topic: Aesthetic/Landscaping Design Blog Where to Place the Link: In the Conclusion (suggesting ways to finish the landscape around the new wall).
