In the old townhouses of southern China, lots were narrow and deep, pressed between neighbors on both sides, with the street just a few steps from the front door. There was no room for a garden, no yard to speak of, so the garden went up — an opening cut into the roof, a gap in the middle of the house where the sky came through. They called it a tian-jing, a sky well. The form dates to the Ming dynasty, originating in the Huizhou and Jiangnan regions, and traveled south with Fujian merchants to Taiwan and Southeast Asia.
Light fell into the center of the house and every room opened onto it. Rain collected there. Air moved through. In the humid summers of the southern coast, the sky well pulled heat upward and drew cooler air in from the edges, less a decorative choice than a way of making the house breathable. It was more architectural than botanical — a piece of sky inside the house, with water and stone below. The best ones made room for both.
What those townhouses solved out of necessity, later Chinese and Taiwanese residential architecture pursued by choice — the courtyard as organizing principle, the fixed point around which a house arranges itself. Rooms don't look out, they look in, and privacy comes not from closing things off but from making the interior world complete enough that the exterior one recedes.
A kitchen that opens onto a courtyard instead of a neighbor's siding. A guest house at the back of the lot, connected by a covered walk that could close in over time. The park visible from the upper floor, the street not visible at all. Concrete, wood, glass wide enough to make the threshold disappear. What you have been describing — requirement by requirement, room by room — is a modern interpretation of the tian-jing house.
A preliminary zoning analysis is the first step in any residential project. Before we draw a single line, we need to understand what the city's rules allow on your specific lot — how large the building can be, where it can sit, how tall it can go, and what types of uses are permitted. This document does that work for 520 129th Ave SE, Bellevue.
We start with your intended program and confirm whether it fits within the zoning envelope. But we also look beyond it — the code often allows more flexibility than homeowners realize, so we include alternative scenarios to make sure you see the full range of what's possible. Whether you use them now, later, or never, they're here for the complete picture.
The intended program is achievable. Your lot supports a single-family residence with a guest suite within the current zoning. The sections that follow explain how.
This analysis is preliminary, prepared to inform early project decisions. All zoning data is based on the Bellevue Land Use Code as of March 2026 and King County public records. Specific figures — setbacks, lot dimensions, slope, trees, and critical areas — will be verified through a land survey, geotechnical report, and arborist assessment during the project. All information should be confirmed with the City of Bellevue prior to design or permitting.
Zoning can feel technical. Before diving into the specifics of your lot, here are the key terms you'll see throughout this document — explained in plain language.
| Zoning | Every lot in the city is assigned a zone. The zone is the rulebook — it says what you can build, how big, and how tall. Your lot is zoned SR-3, which means single-family residential. Everything in this document comes from that rulebook. |
| Floor Area Ratio (FAR) | You'll hear this term a lot — it sounds technical, but the idea is simple. FAR tells you how much you can build on your property. The city uses it so that homes in a neighborhood stay at a similar scale. It doesn't matter how the area is distributed or across how many floors — it's the total that counts. This is almost always the number that limits what you can do. The math: FAR is just a ratio of your lot size. A 10,000 SF lot with a FAR of 0.50 means you can build up to 5,000 SF total. |
| Setbacks | Setbacks determine how close you can build to the street, to your neighbors, and how big your yard needs to be. Think of each side as a required yard — front yard, side yards, back yard. Each has a minimum distance you have to keep clear. What's left after all the setbacks is where you're allowed to place a building. |
| Lot Coverage | The building's footprint — how much of the lot is covered by the building. If you looked straight down from above, lot coverage is the percentage of your property that has a roof over it. Building taller instead of wider is one way to stay within this limit. |
| Building Height | How tall the building can be, measured from the ground to the top of the roof. Pitched roofs get more height allowance than flat ones, because much of that extra height is just the shape of the roof, not livable space. |
| ADU / DADU | There are lots of acronyms in city codes — this is one of them. ADU stands for Accessory Dwelling Unit, which is essentially a second home on the same lot. A guest suite, a rental, an in-law apartment. It can be attached to the main house (like a basement suite or above-garage unit) or detached as its own building in the yard. When detached, it's called a DADU. The type you choose may change your FAR (see above), which we'll get into later. |
| Max Development Potential | This term doesn't usually appear in the zoning code itself, but it's one of the main reasons to do this analysis. Once you understand the rules — FAR, setbacks, coverage, height — you can calculate how much you are legally allowed to build, or, in other words, the Maximum Development Potential of your property. This number may be higher than what FAR alone suggests, because certain configurations (like adding ADUs or additional units) unlock additional area allowances. |
| Middle Housing | "Middle Housing" comes from "Missing Middle Housing" — a building type that has historically been missing between single-family homes and large apartment complexes in the region. It includes duplexes, triplexes, fourplexes, and cottage housing. A recent Washington State law now allows these on lots that were previously limited to one home. Why does this matter? Your lot may allow you to build more than you think, and it's worth understanding what's possible even if a single-family home is the goal. |
All of these rules (and others) apply at the same time. Your project has to satisfy every single one — you can't go over on one just because you're under on another.
| Tax Parcel No. | 326000-0120 | King County Records |
| Plat | Heritage Lane No. 1, Block 2, Lot 3 | |
| Lot Area | 7,350 SF | |
| Lot Dimensions | ~70 ft wide × ~105 ft deep | Quarter Section Map |
| Existing Home | Yes, built 1967 | Asbestos abatement required (pre-1980). |
| Slope | Lot appears to be relatively flat | TBC with site survey. |
| Critical Areas | TBC | TBC with geotech report. |
| Utilities | Public water, public sewer, paved road | |
| Watershed | Cedar River / Lake Washington. Kelsey Creek drainage. | Districts & Development Report |
| Trees | There appears to be one significant conifer in the front yard. Mature trees on adjacent properties may have root protection zones extending onto the parcel. | TBC with arborist report. LUC 20.20.900 |
| Zoning | SR-3 | Chart 20.20.010 |
| Overlay | None identified | |
| Permitted Use | Single-Family Residential | |
| Min. Lot Area | 8,500 SF | Lot is 7,350 SF — nonconforming but qualifies as building site per LUC 20.20.070. |
| Density | 4 du/acre | 1 SFR + up to 2 ADUs · 1 SFR + up to 2 DADUs · Middle Housing — up to 4 units |
| Setback — Front | 20 ft | Chart 20.20.010 |
| Setback — Rear | 25 ft | Chart 20.20.010 |
| Setback — Side | 5 ft (one) / 15 ft (combined) | Chart 20.20.010 |
| Max Height | 30 ft flat / 35 ft pitched roof | Measured to avg. existing grade. Max façade height 40 ft. Chart 20.20.010 |
| Max FAR | 0.50 | 7,350 × 0.50 = 3,675 SF. LUC 20.20.390, Table B.1 (1 unit, lots ≤10,000 SF) |
| Max Lot Coverage | 35% | 7,350 × 35% = 2,572 SF. Chart 20.20.010 |
| Max Hard Surface | 75% | 7,350 × 75% = 5,512 SF. Chart 20.20.010 |
| Max Impervious | 45% | 7,350 × 45% = 3,307 SF. Chart 20.20.010 |
| Greenscape | 50% of front yard setback | Chart 20.20.010 |
The intended program is a primary home and a secondary unit on the same lot.
The secondary suite can be configured as an Attached ADU (built within or connected to the main house) or a Detached ADU (a separate structure in the yard). Both are permitted under the current zoning. The difference is in how the code counts the area, which affects how much you can build in total.
The secondary unit is part of the main house — a basement apartment, an above-garage unit, or a connected wing. Because it's attached, it does not count toward FAR or as an additional dwelling unit. The code gives you the base allowance for the primary residence, plus up to 1,200 SF for the secondary unit on top of that.
| FAR | 0.50 | ADU exempt from FAR. LUC 20.20.120 |
| Primary Residence | up to 3,675 SF | Lot area × FAR |
| Secondary Unit | up to 1,200 SF | Exempt: does not count against FAR. ADUs over 1,000 SF may require on-site parking. |
The secondary unit is a separate, freestanding structure — a backyard cottage or carriage house. Because it's independent, it counts as an additional dwelling unit, which increases the base FAR. The total allowable area is then shared across both buildings. You choose how to split it.
| FAR (adjusted) | 0.60 | 2 units increases FAR. LUC 20.20.390 |
| Primary + Secondary | up to 4,410 SF | Lot area × FAR — shared across both structures |
| Secondary Unit Cap | up to 1,200 SF | 24 ft height limit. 5 ft rear setback. ADUs over 1,000 SF may require on-site parking. |
The goal of this analysis is not necessarily to maximize area — it's to understand what the code allows so you can make the best decision for your project. Sometimes that means building as much as possible; sometimes it means choosing a configuration that better suits the site, the program, or the way you want to live. The numbers above give you the range. The design process is where those numbers become a home.
The zoning code allows more flexibility than most homeowners realize. Beyond a single home with one ADU, you may be entitled to up to two accessory units or — under recent state legislation — multiple standalone dwelling units. These scenarios don't change your intended project, but they represent real development potential worth understanding.
Bellevue allows up to two accessory dwelling units per lot, in any combination of attached and detached. Each is capped at 1,200 SF. Attached ADUs add area on top of the base FAR. Detached ADUs increase the base FAR, and the total is shared across all structures.
Attached ADUs sit outside the FAR calculation entirely — their square footage (up to 1,200 SF each) stacks on top of the primary home's allowance. Detached ADUs increase the base FAR, and the total is shared across all structures on the lot. LUC 20.20.120, LUC 20.20.390
As of 2025, Bellevue allows more than one home on lots that were previously single-family only, following state legislation (HB 1110) adopted locally under LUC 20.20.538. We include this section as a courtesy — it's not part of your intended program, but it's worth understanding what the code now allows. You can discard this entirely if it's not relevant to your goals.
Under these rules, your lot could support up to four units — duplexes, triplexes, fourplexes, cottage housing — as standalone homes, not just through ADUs. As the unit count goes up, so does the allowable FAR. Four units nearly doubles the total buildable area compared to a single home. The dimensional standards also loosen: front and rear setbacks drop to 10 ft, lot coverage goes to 40%, and height adjusts to 32 ft flat / 35 ft pitched.
Max Area Total = Lot Area × FAR. Up to 2 attached ADUs may be added on top of any middle housing scenario without affecting FAR or the unit count. FAR per LUC 20.20.390, Table B.1 (lots ≤10,000 SF). Middle housing standards per LUC 20.20.538.
To move from this preliminary analysis into design, the following steps are recommended:
For a broader overview of the custom home process — from early planning through construction — our Residential Guide covers what to expect at each stage.
View Residential GuideReach out anytime — av@metrica.us
Andrés