Product Field Work All builds
BuildGrounded

Can I Build Here?

Tacoma now allows two backyard homes on almost any residential lot. Whether one fits on yours depends on a dozen rules, your lot’s exact shape and where your house sits. This build applies the city’s rules to the county’s parcel map and draws the answer on the lot.

The problem

The rules for a detached backyard home (an ADU) are spread across a city web page, two zoning tip sheets and several code sections. None of them can tell a homeowner whether a unit fits on their lot, because that depends on geometry: the lot’s shape, the alley, the house’s footprint. Most people find out after paying a designer or waiting for a pre-application meeting.

–building permit applications for ADUs in Tacoma in 2025, from the city’s permit data
–median days from application to issued permit in 2025
–of the real lots sampled here can’t be answered by rules alone, most of them corner lots

A wrong early answer is expensive either way. A homeowner who is told “probably” pays for plans that don’t fit; one who is told “probably not” never applies.

How I measure the problem
  1. Share of real lots where a unit clearly fits, clearly doesn’t, or needs a person, on a random sample of city lots
  2. Minutes a planner spends answering one feasibility question by hand, an assumption you can change below
  3. Whether every limit on the answer points to its source, so a planner can check it in seconds
Why I chose it

It turns legal text into geometry, which is where “grounded” stops being a slogan: a setback either keeps a building five feet from the line or it doesn’t. It’s also local, public, and something I can check by walking down the street.

The ideaWrite the city’s rules down once as a small, cited rulebook. Let code apply them to each lot’s real shape. Hand every case the rules can’t settle to a person, with the exact question to ask.

Sources: City of Tacoma ADU standards (content current as of Aug 7, 2026); UR-1 and UR-2 District Development Standards tip sheets (TMC 13.06.020.F, 13.06.080.A); City of Tacoma Accela permit data, applications through .

Real Tacoma lots, checked against the rules

Where a backyard home can go House Other buildings Largest footprint that fits

What the answer is worth

For the city’s permitting staff, who answer “can I build an ADU here?” at the counter, by phone and in pre-application meetings. The share answered by rules is measured on the sample above.

–of planner time saved a year
–planner hours a year on feasibility, down from
–questions a year still go to a planner, with the question already written

    From public data

    Median pay for urban and regional planners, BLS, May 2024.

    Private industry, BLS ECEC, June 2026; public-sector benefits run higher, so this is conservative.

    Assumptions you can change

    No public benchmark exists for these. They are conservative starting points, not findings.

    What it means for the people

    Today, city planners pull up each parcel, measure it and read the code aloud to homeowners who mostly have the same question. Here is how that year shifts.

    Today
    Answering every feasibility question by hand
    With the drawing
    Confirming answers
    Hard cases
    Freed for permit review

    Homeowners arrive knowing the shapeThey see where a unit can go before paying anyone, and the meeting starts from a drawing instead of from zero.
    Planners get the hard lotsCorner lots, odd shapes and historic districts come with the specific question already written, so the conversation is about judgment, not measuring.
    Designers start from a real envelopeThe largest footprint that fits is a starting constraint, not a surprise at plan review.
    What disappears, and what doesn’t

    Measuring setbacks by hand for clear-cut lots goes away. Deciding which side of a corner lot is the front, reviewing critical areas and trees, and approving the permit stay with the city.

    How it works

    Public mapsCounty parcels, city zoning, 2024 building footprints and right-of-way lines.
    Cited rulebookThe city’s standards, drafted from its documents with Claude and checked line by line against the source.
    Geometry, then hand-offCode finds the street, the alley and the rear yard, and applies setbacks. Corner and odd lots go to a person.
    The drawingWhere a unit can go, the largest footprint that fits, and every limit with its source.

    Evidence

    –real single-family lots sampled at random across Tacoma’s UR-1 and UR-2 zones
    –clearly have room for at least a 300 sq ft unit, the size of the city’s smallest pre-approved plan
    –back onto an alley, where the rear setback drops from 15 feet to zero
    What I haven’t proven yet

    No planner has checked these drawings yet; that’s the next step, on 50 lots. The 2024 footprints miss anything built since. The rules don’t cover critical areas, easements, utilities, tree credits or fire separation, so every answer lists them as questions for the city. And corner lots are handed off rather than guessed, which is why so many lots need a person.

    Choices

    A cited rulebook over a chatbot reading the codeA model is good at drafting the rulebook and bad at doing geometry. So it drafted, a person checked, and code does every measurement.
    Hand off corner lots instead of guessingWhich side is the front changes every setback. Guessing would look confident and be wrong a third of the time.
    Blocks, not house numbersThe lots are real and public, but a portfolio has no reason to point at anyone’s house.