Housing model profileD0
Low-cost backyard cottage
1 new home, existing house kept
A compact one-story cottage in the back yard — a rental, a home for family, or future flexibility. Modeled on simple, repeatable DADU plans and current backyard-cottage cost benchmarks.
Urban Acupuncture housing model
Repeatable program, parcel screening, schematic placement, and economics model — not City-pre-approved construction drawings.
- Homes
- 2
- Building type
- One 480 square foot, one-story backyard cottage
- Existing house
- Keep as-is
- Typical new footprint
- 16 × 30 ft
- New-building height
- 1 story
- New-home bedrooms
- 1 bedroom
- You end up with
- 1 new home, existing house kept. Keep the house; add a simple 16 × 30 foot detached home.
- You put in
- Renovation or construction funds, cash or borrowed; ongoing operating costs. Get a site-specific budget before committing.
- Your role
- Owner commissioning the work; landlord if rented, or host for family housing.
- Timeline
- Interior/site assessment → design and permits → construction → occupancy. Ask the designer and contractor for durations; no project schedule is established here.
- It works when
- A detached accessory dwelling unit is allowed on the lot; The rear yard can hold a 16 × 30 foot cottage and required clearances; Construction access and utility connections are practical.
- Main uncertainty
- Renovation/site costs and rent may leave a monthly loan shortfall. Family use does not produce rental income.
- Next step
- Bring measured plans or a survey to a residential designer, then request a contractor budget and financing proposal.
Representative site plan
New: one 16×30 ft cottage. Drawn on a typical lot — every real lot differs, so this is illustrative, not a site-specific layout.
The program
2 homes — 1 market cottage (16x30 ft) in the rear yard.
+1 net new home per lot (market-rate).
Workbook-baseline economics
This cottage costs $275K–$425K in the workbook scenarios. Paid in cash, the base case yields 4.5% annually before financing. Family use and rental income are different choices.
- Modeled all-in cost
- $275K–$425K
- Cash-funded annual yield on cost
- 4.5%
- Does it pencil?
- Cash-flow shortfall if fully financed
- What to check first
- Parcel-specific inputs
Simple-site low case through difficult-site high case.
Annual net operating income $14K; simple payback 22 years. Excludes financing, reserves, income tax and appreciation.
Illustration: borrow 100% of the $315K base cost at 7% over 30 years. Payment $2K/mo versus $1K/mo net operating income; edit assumptions in the rental comparison.
Representative workbook baseline — not adjusted for a specific parcel.
Illustrative workbook baseline — a real packet adjusts these with the parcel's own assessor, market, and rent data.
Cash-funded vs. financed rental
Uses the $315K base cost and $1K/mo net operating income, after vacancy, operating costs and added property tax. The 100% loan share, 7% rate, 30-year term are editable illustrations, not financing offers or market estimates.
- Cash-funded annual yield on cost
- 4.5%
- Monthly cash flow after loan
- −$922/mo
Before financing and owner income tax; annual NOI $14K.
Loan payment $2K; initial cash $0.
Include design, permits, utilities, tax, contingency and construction-period financing in the all-in budget. This amortizing-loan comparison excludes loan fees, replacement reserves, owner income taxes and appreciation. Family occupancy produces no rent; enter zero rent to model it.
Where it fits
Lots where a backyard cottage (DADU) is allowed and the rear yard is clear enough for a small one-story home, with no transit requirement. The existing house stays; the cottage is a market-rate rental, so the public benefit is gentle, broadly available added density rather than an income-restricted home.
What must be true
- A detached accessory dwelling unit is allowed on the lot
- The rear yard can hold a 16 × 30 foot cottage and required clearances
- Construction access and utility connections are practical
Verify before relying on it
- Current Seattle DADU rules and site-specific permit requirements
- Trees, drainage, utility route, access, and foundation conditions
- Licensed construction drawings and contractor pricing
Check Low-cost backyard cottage at a Seattle address
Choose a parcel to open this exact model in the feasibility packet. We will test its screening match, place the program schematically, and adjust the economics with parcel data.
If the plan does not pass this parcel's screening, the packet will say so and offer other paths.
Closest Seattle pre-approved plan references
D0 is Urban Acupuncture's 16 x 30 ft site-and-financial model, not an architect's construction set. These City-listed plans explore a similar compact-cottage idea. Their exact parcel fit, current Standard Plan status, licensing, and site-specific permit work still need confirmation.
MADADU
Magellan Architects
14 ft 8 in x 35 ft 11 in ground footprint / 527 sq ft
MOA Family ADU
Mobile Office Architects
16 x 26 ft ground footprint / 850 sq ft
Funding and programs that may apply
Programs that may pair with this plan
Matched from plan facts only. Parcel geography, income, utility territory, and owner facts can change the final list.
Seattle Pre-Approved DADU Plans
Seattle SDCI / OPCD ADUniverse
Pre-reviewed design plans intended to reduce design cost and speed review for eligible detached ADU projects.
$1,000 / project
Home Improvement Property Tax Exemption
King County Assessor / RCW 84.36.400
Temporary property-tax exemption on qualifying added improvement value.
Exempts added value up to 30% of original structure value
Washington State HEAR Electrification Rebates
Washington Department of Commerce / local HEAR administrators
Administrator-run rebates for eligible electrification equipment and installation. Measures, amounts, coverage and available funding vary by local administrator.