If you own property in the Snoqualmie Valley — or you're considering buying here — understanding the distinction between an ADU and a DADU isn't just a vocabulary exercise. It directly affects what you can build, how large it can be, how close it can sit to your property lines, how it gets permitted, and whether it's feasible at all on your particular parcel.

These questions come up constantly in my practice. A seller wants to know if their property could support a rental cottage before they list. A buyer wants to know if they can house aging parents on the same lot. An investor wants to understand what their income potential looks like after closing. And in every case, the answer begins the same way: what jurisdiction are you in?

Because the rules in the City of North Bend are not the same as the rules in the City of Snoqualmie. And the rules for Fall City — which is not a city but an unincorporated community governed by King County — are different from both.

Why This Matters Right Now: The Housing Crisis Context

Washington State is in the middle of a housing affordability crisis that is not abstract — it shows up in real ways for real families in the Snoqualmie Valley. The average income required to qualify for a median-priced Washington State home is nearly $176,000 per year, while the average Washington household earns roughly $94,600. Put plainly, homeownership is out of reach for approximately 75% of Washington families based on current prices and lending standards.

The state has set a goal of 1.1 million new homes over the next two decades. And one of the most immediate, practical tools available to existing homeowners is the ADU — small, relatively affordable to build, and possible to develop without buying additional land. ADU permitting statewide has been climbing steadily since 2020, and legislative changes enacted in 2023 are accelerating that trend.

The Game-Changer: Washington's House Bill 1337

In 2023, the Washington State Legislature passed House Bill 1337 — one of the most significant changes to residential land use law in the state's recent history. For King County, the changes took effect by June 30, 2025. If you haven't updated your understanding of ADU rules since before that date, you may be working with outdated information.

Here is what HB 1337 requires statewide for all jurisdictions within Urban Growth Areas:

• Cities and counties must allow at least two ADUs per residential lot in all areas where single-family homes are permitted. This can be two attached, two detached, or one of each.
• The maximum ADU size must be at least 1,000 square feet. Local governments can no longer cap ADUs smaller than that floor.
• Owner occupancy requirements are eliminated. You can rent both your primary home and your ADU or DADU independently. No annual affidavit required.
• Impact fees are capped at 50% of what would be charged for the primary residence. For ADUs under 750 square feet, fees may be further reduced or waived.
• No parking requirements may be imposed for ADUs, with limited exceptions.
• Existing structures — including garages — may be converted into ADUs regardless of current setback or lot coverage nonconformities.
• ADUs may be sold separately from the primary home as condominiums, opening a new avenue for property owners to monetize or transfer these units independently.
• Cities must approve compliant ADU applications within 60 days, streamlining what was often an unpredictable permitting timeline.

Jurisdiction First: The Question That Changes Everything

Before you spend a dollar on plans or consult a contractor, you must answer one question: what jurisdiction is your property in? In the Snoqualmie Valley, there are three distinct answers, each with its own rulebook.

Side-by-Side: How the Rules Compare

The table below reflects current regulations as of mid-2025, following HB 1337 implementation. Always verify with the applicable jurisdiction before proceeding — codes are actively evolving and individual parcels may carry additional constraints tied to critical areas, septic, or zoning overlays.

The Rural Zone Variable: Why Acreage Doesn't Guarantee Approval

One of the most common misconceptions I encounter is the assumption that because a rural parcel is large — say, five or ten acres — there's plenty of room to add a DADU. Size helps. But size alone doesn't determine eligibility. Here's what actually governs rural ADU feasibility in unincorporated King County:

Zoning Designation

Rural Area zones in King County are designated RA-2.5, RA-5, RA-10, or RA-20, reflecting the minimum lot size in acres. A DADU is generally allowed in RA-2.5 and RA-5 zones if the parcel meets the minimum acreage. In RA-5 and RA-10 zones, the minimum is typically five acres. There is also a mechanism in RA-5 zones where a detached ADU may be permitted on a 2.5-acre parcel if the owner purchases a Transferable Development Right (TDR) from the rural area — an option worth exploring with a land use professional.

Septic System Capacity

This is the sleeper issue of rural ADU development, and it surfaces constantly in my transactions throughout the upper valley. A second dwelling unit — even a small one — typically adds significant demand to the existing on-site sewage system. King County Public Health must confirm that the existing system can handle the additional load, or that a new or expanded system can be permitted. If the lot has a single, older conventional septic system with limited reserve area, this may be the single factor that stops a DADU project in its tracks — regardless of zoning, lot size, or setbacks.

Well Water

On properties served by a private well rather than public water, the well must demonstrate adequate flow to serve both the primary dwelling and the ADU. A flow test and potability confirmation are typically required before King County will approve the permit.

Critical Areas

Many Snoqualmie Valley parcels contain or adjoin critical areas — wetlands, streams, steep slopes, landslide hazard areas, or flood zones. Critical area buffers can substantially reduce the buildable footprint of a property. A DADU cannot be placed within a critical area or its buffer, which on some rural lots can eliminate most or all of the usable land.

What You Can Realistically Build — and What It Might Cost

ADU and DADU construction costs vary significantly based on type, size, finishes, site conditions, and whether you're building new or converting an existing structure. In the Snoqualmie Valley, where contractor access can affect pricing and septic work is often required, budgeting conservatively is wise. Here are rough ranges to orient your planning:

As context: studios in North Bend currently rent for roughly $1,400–$2,200 per month. One-bedroom units range from $1,800–$2,800. At the higher end of that range, a well-positioned DADU can generate meaningful rental income that offsets carrying costs or contributes materially to your overall household cash flow.

The Notice on Title: A Step Buyers and Sellers Often Miss

Both the City of North Bend and unincorporated King County require that a Notice on Title be recorded before an ADU permit is issued. This is a legal document filed with the county that identifies the secondary unit as an accessory dwelling — not a separate primary dwelling — and runs with the land permanently.

Why does this matter in a real estate transaction? Because if a property has an unpermitted ADU or DADU — a unit that was built and occupied without permits — it may not have a Notice on Title on record. This creates liability exposure for sellers, potential lender issues for buyers, and code compliance obligations that can be complex and costly to resolve. It is a standard part of my due diligence review on any property in this area that appears to have a secondary structure or living space.

My Bottom Line for Snoqualmie Valley Property Owners

ADUs and DADUs represent one of the most significant opportunities available to residential property owners in this area — both as housing for family members and as income-generating assets. The regulatory environment has genuinely improved with HB 1337, and the trend line continues in the direction of fewer barriers and more flexibility.

But the details matter enormously. A DADU that is completely feasible on a city lot in North Bend may be impossible on a rural parcel in Fall City due to septic constraints. A garage conversion that would sail through permitting in Snoqualmie might require additional design review in North Bend's downtown zones. The only way to know what's actually possible on a specific parcel is to look at the specific parcel — its zoning, its jurisdiction, its critical areas, its utility infrastructure, and its current development conditions.

That's the work I do with my clients every day. If you're evaluating a property for ADU or DADU potential — whether you're a buyer, seller, or existing homeowner — I'd welcome the conversation.