Can You Build a DADU in Snoqualmie’s Floodplain?
Snoqualmie’s ADU checklist says new residential construction is not permitted in the floodway. A floodplain site outside the floodway has a different path, with elevation, drainage and flood-permit requirements.
Sources checked November 5, 2026. Confirm the requirements for your parcel with its permitting authority.
What is the city’s floodway distinction?
The city checklist separates the floodway restriction from floodplain sites outside the floodway. Establish the mapped location for the actual cottage footprint. A general statement that the property is near the river is not enough to choose the correct path.
Keep the mapping and staff determination with the proposed site plan. If the site has more than one possible building location, identify the conditions affecting each before deciding where to invest in detailed design.
Official guidance: Snoqualmie ADU checklist, revised August 19, 2026.
What does the checklist require outside the floodway?
| Floodplain item | Published requirement |
|---|---|
| Elevation | ADU one foot above the 100-year base flood elevation. |
| Evidence | Elevation certificate from a certified land surveyor or engineer. |
| Approval | Flood improvement permit for new floodplain development. |
| Drainage | A TIR for floodplain projects; new impervious area is subject to drainage review. |
The checklist also identifies a drainage-report threshold of 2,000 square feet of new plus replaced impervious area. That area test is not a substitute for the floodplain-specific review. Use the city’s current requirements for the design.
Official guidance: Snoqualmie ADU checklist, revised August 19, 2026.
How does this change the early site discussion?
Evaluate the entrance, foundation relationship and the route between the homes together. If the floor must be elevated, a plan that looked convenient at yard level may need a different access arrangement. Discuss that before finalizing room layouts.
Ask the survey and design team to use the same elevation reference. Keep the required certificate, architectural elevations and foundation information coordinated so the application does not present conflicting levels.
What should the first budget include?
Identify survey and elevation work, the foundation concept, access, drainage design and the additional approval tasks. State which of those have been investigated and which remain assumptions. Avoid comparing this proposal with a simple level-site building price without reconciling the scopes.
TimberworX can discuss a Snoqualmie property in a free initial consultation. Detailed feasibility, design and budgeting are paid preconstruction work, with the next tasks agreed before they begin.
A few things to know
Does being outside the floodway remove every flood requirement?
No. A floodplain location outside the floodway still has the city’s applicable elevation and approval requirements.
Is the cottage roof the only area counted for drainage?
Use the project’s full new and replaced impervious-area calculation and applicable site triggers.
Keep planning
Snoqualmie DADU Permits: The Application Checklist
Use Snoqualmie’s August 2026 DADU checklist for building plans, water and sewer forms, drainage review and flood-related approvals.
Do you need a survey for a DADU?
Understand how a DADU site plan differs from a survey and which property information supports design and permit review.
DADU stormwater and drainage planning
Understand why roofs, paths, driveways, soil conditions and construction disturbance belong in an early DADU drainage discussion.