ADU Planning & Permitting
Accessory dwelling units, from what's allowed to what's permitted
Washington has spent several years loosening ADU rules, and jurisdictions have implemented that unevenly. What your lot allows depends heavily on who permits it.
Start with what the lot allows, not what the plan looks like
The common expensive mistake is buying or designing a plan first. Lot size, setbacks, height limits, existing coverage, parking requirements, utility connection capacity, and critical area buffers all constrain where an ADU can go and how big it can be — and those constraints frequently rule out the plan someone already paid for.
A short zoning and siting analysis answers the question for a fraction of what a redesign costs.
Attached, detached, or garage conversion
Each carries different code implications. Detached units are separate structures with their own setback, height, and sometimes separate utility service requirements. Attached units interact with the existing structure's fire separation and egress. Garage conversions bring existing-conditions issues — foundation, ceiling height, and whether the original structure was permitted at all.
The right choice is usually driven by site constraints and utility costs, not preference.
Where ADU projects get stuck
Sewer or septic capacity is the most common one. Existing septic systems often can't support an additional bedroom count without redesign or replacement, and that finding routinely arrives after design is complete. Others: side sewer routing, power service upgrades, driveway and access requirements, and stormwater thresholds triggered by the new impervious area.
What you get
- Zoning and siting analysis for your specific parcel
- Attached vs. detached vs. conversion recommendation
- Utility capacity review — sewer or septic, water, power
- Design team coordination and plan review readiness
- Permit application and correction response management
- Construction oversight if you want it carried through
Bring CLD in when
- You want to know if an ADU is possible before spending on plans
- You're on septic and don't know if it supports another unit
- A permit application came back with corrections
- You're weighing a detached unit against a garage conversion
Common questions
Can I build an ADU on my lot?
Most likely — Washington has broadly expanded ADU allowances — but the specifics depend on your jurisdiction's implementing code, your lot dimensions, and your utility situation. A siting analysis gives you a definite answer for your parcel.
What usually kills an ADU project?
Septic capacity, followed by setbacks that leave no viable building envelope, followed by utility connection costs nobody budgeted.
Can you manage the build too?
Yes. Many ADU clients engage CLD for feasibility and permitting, then continue into construction oversight so the same person carries the project through.
Where this service is available
In person across Snohomish County · King County · Skagit County · Island County. Code research and submittal preparation for this scope is also available remotely, nationwide.
Related
Services that usually go with this one
Permitting & Entitlements
Plan review is a conversation with a reviewer who has a checklist and a queue. Projects move when someone reads what's actually being asked and answers it completely.
Read more →Feasibility & Due Diligence
The cheapest problem is the one you find before closing. A feasibility review tells you what the parcel supports, what it will cost to get there, and whether to walk away.
Read more →Construction Oversight & Quality Control
The approved drawings describe what should get built. Oversight is the process of confirming, repeatedly, that it is.
Read more →Tell Carol about the project
The first conversation is a straight read on whether the project is workable and what it would take to move it. No charge for that call.