Retaining Walls & Rockeries

See also: See also: Decks, Fences, Grading Permit, Sheds

What Is It?

A retaining wall is a structure designed to support soil at a steeper angle than the soil could stand on its own; it may or may not be attached to a building. A rockery consists of placed rocks used to control soil erosion.

What Permits Do You Need?

You don’t need a construction permit if you meet all of the following three conditions:

1. The rockery or retaining wall will be 4 feet or lower in height as measured from the bottom of the footing (even if under grade) and the top of the wall
2. The wall is not located in an environmentally critical area (ECA) or near an ECA
3. You will not damage adjoining properties or structures during or after construction of the wall

If you don’t meet these three conditions, you need a new construction permit. For example, if you are building a wall at the property line, the potential for damage may exist and you need a construction permit.

• Tip 103, Site Plan Requirements

You may also need a grading permit depending on the amount of soil you plan to move or the area you plan to disturb.

Research the Code

• Rockeries and retaining walls don’t contribute toward your lot coverage limit. This limit is the percentage of your lot that can be covered by a house and other buildings, such as garages, or impervious surfaces, such as paving.
• You cannot build a rockery or retaining wall of any height in an ECA unless you meet very specific requirements or obtain an exemption. Rockeries and retaining walls are not eligible for small project waivers.
• Rockery designs must be prepared by a geotechnical engineer or comply with the prescriptive rockery installation design standards.
• You need a side sewer permit if you plan to install drainage behind your wall and connect it to a side sewer. See the Subsurface Drainage Systems section of Director's Rule 4-2011, Requirements for Design & Construction of Side Sewers (Drainage & Wastewater Discharges).
• If building near a property line or public right-of-way, you must ensure the retaining wall or rockery is built on your property. If you build within the right-of-way, you must follow additional requirements. See the Seattle Right-of-Way Improvement Manual for more information.

• Tip 321, Rockeries: Prescriptive Design and Installation Standards
• Tip 327A, Environmentally Critical Areas Exemptions, Relief from Prohibition on Steep Slope Development, and Modifications to Submittal Requirements
• Tip 508, Grading and Retaining Wall Construction Near or Adjacent to Property Lines

Should You Hire a Professional?

• Rockery and retaining wall drawings commonly require a professional stamp (indicating they were designed by an architect or engineer). If your rockery or retaining wall does not require a professional stamp, you can prepare the drawings yourself or hire a professional.