Most single-family residential lots in Kirkland can have up to two ADUs in addition to the primary home. That follows Washington HB 1337, the 2023 state law requiring cities of Kirkland’s size to allow two accessory dwelling units per lot in residential zones.

Common configurations include one attached ADU (an AADU, such as a basement apartment or addition) plus one detached ADU (a DADU, such as a backyard cottage), or two of either type where lot dimensions allow. Lot size, setbacks, lot coverage, and floor area ratio still govern what physically fits.

Under HB 1337, Kirkland cannot impose a minimum lot size for an ADU beyond what the underlying zone already requires for the primary residence. If your lot is legal for a single-family home, it is generally eligible for at least one ADU.

The practical limits are dimensional rather than area-based: setbacks (typically 5 feet from side and rear lot lines for a DADU), maximum lot coverage, and floor area ratio determine how much building footprint is left after the existing home. Smaller lots may only have room for an attached ADU or a compact DADU.

Kirkland caps an ADU at 1,000 square feet of gross floor area, or the size allowed by floor area ratio and lot coverage limits — whichever is more permissive. HB 1337 prevents cities from setting an ADU size smaller than 1,000 square feet, and Kirkland adopts that standard.

Height is generally limited to two stories or roughly 24 feet for a DADU, depending on the underlying zone and roof type. The checker on this page estimates your remaining buildable footprint based on the 50% FAR cap typical of RS zones, but a survey and site plan are required to confirm what will actually permit.

It depends on transit proximity. Under HB 1337, Kirkland cannot require off-street parking for an ADU if the property is within a half-mile walk of a major transit stop. Lots farther from transit are typically required to provide one off-street stall per ADU, but many properties qualify for the waiver.

If on-street parking is available on your block and the lot is close to frequent bus service, the parking requirement often disappears entirely. The checker tool flags this based on the transit and on-street parking inputs.

Yes for long-term rentals. HB 1337 prohibits Kirkland from requiring the property owner to live on site, so you can rent both the primary home and the ADU to separate households. The ADU also cannot be required to be sold together with the main house, which preserves resale flexibility.

Short-term rentals (Airbnb, VRBO, stays under 30 days) are regulated separately under Kirkland’s short-term rental ordinance and may require a license, primary-residence status, or other restrictions. Always verify current STR rules with the city before listing — these change more often than the underlying ADU code.

Plan on 4 to 8 months for permits on a straightforward DADU in a standard RS zone, and 6 to 12 months if your lot has critical areas, shoreline jurisdiction, or other site complications. Construction typically adds another 5 to 9 months depending on scope and contractor availability.

Kirkland reviews ADU permits administratively (no public hearing) when the proposal meets code, which keeps the timeline predictable. Pre-approved DADU plans, where available, can shorten review meaningfully.

Construction costs in Kirkland generally run $350 to $550 per square foot for a quality DADU as of recent build cycles, which puts a 700 to 1,000 square foot detached unit in the rough range of $250,000 to $550,000 all-in. That includes design, permits, site work, utilities, and finishes — but the spread is wide depending on slope, soil, utility runs, and finish level.

An attached ADU built into existing space (a basement conversion, for example) is typically less because the shell is already there. Site-specific bids from a builder familiar with Eastside permitting are the only way to get a reliable number.

Yes. King County reassesses the property after construction is complete and the assessed value will reflect the added square footage, finishes, and rental potential. The exact bump depends on what you build and current millage rates, but a new DADU typically increases the annual tax bill by several thousand dollars.

Some owners offset this through rental income from the ADU. Run the numbers including the higher tax basis, insurance increase, and any new utility connection fees before deciding whether the financials work for your goals.

Generally no — under standard ADU rules in Kirkland, the accessory unit and primary home stay on a single tax parcel and transfer together at sale. Washington’s condominium-style ADU sale provisions (sometimes called unit lot subdivisions or ADU condominiumization) are evolving at the state level, and a few jurisdictions are piloting separate sale, but it is not yet a routine path in Kirkland.

That said, an ADU adds resale value and rental income potential to the parent property. For owners who want to physically separate the parcels, a short plat or unit lot subdivision may be possible on larger lots — that is a separate, more involved process from building the ADU itself.

The most common project-killers are site conditions rather than zoning denials. Watch for:

• Critical areas — wetlands, steep slopes, geologic hazard zones, or stream buffers can eliminate buildable area on what looks like an open backyard.
• Shoreline jurisdiction — lots within 200 feet of Lake Washington or other shorelines trigger a separate, longer permitting track under the Shoreline Management Act.
• Tree retention — Kirkland’s tree code may require keeping certain trees, which restricts where a DADU can be sited.
• Sewer and side sewer capacity — older neighborhoods sometimes need a side sewer upgrade before an ADU can be permitted.
• HOA or CC&R restrictions — even when the city allows two ADUs, a private covenant on the property may not. Always read the recorded CC&Rs before designing.

The checker on this page flags the city-level constraints. Pulling a title report and confirming utility capacity early is what catches the rest.