Before you call a builder, price a loan, or sketch anything on a napkin, there is one question that decides whether your project is even possible: does your zoning allow it on your specific parcel? The honest answer is that you can confirm most of it yourself, for free, in about an hour, using public tools. Most ADU and addition projects do not fail during construction. They fail during early planning, when an owner spends money on a design that the setbacks, lot coverage, or a recorded easement were never going to allow. This guide shows you how to check, in plain order, before a dollar leaves your account.
The short answer: can you build an ADU or addition?
Whether you can build an ADU or an addition depends on five things working together: your jurisdiction, your zoning district, your lot's dimensions, what structures already exist on it, and any private restrictions recorded against your deed. No single one of these answers the question alone. A lot can be zoned correctly and still be unbuildable because existing structures already consume the allowed coverage, or because an easement eats the only spot the new structure would fit. The goal of a zoning check is to test all five before you design.
Step 1: Find your zoning district and parcel record
Start with your parcel, the legal unit of land you own, identified by a parcel number, sometimes called an APN or parcel ID. You can find it on your property tax bill or through your county's online property records. With that number, two public resources tell you most of what you need.
The first is your local government's zoning map, published by the city or county planning department, which shows the zoning district your parcel falls in, such as a single family residential designation. The second is the zoning ordinance, the actual code text, which lists what is permitted in that district and the dimensional rules that apply. Together these answer the first gate: is an ADU or addition even an allowed use in your zone? In many places a detached ADU is now permitted in single family zones where it once was not, but that is exactly the kind of thing you confirm rather than assume.
Step 2: Understand the four numbers that define what fits
If the use is allowed, the size and placement of what you can build come down to a handful of dimensional standards. These are the numbers that quietly decide your project.
Setbacks are the required distances between a structure and your property lines, typically specified as front, rear, and side. They carve out the area where you are actually allowed to build. Detached ADUs often get reduced setbacks compared to a main house, sometimes as little as a few feet at the rear and side, but the figure is set by your local code and you have to read it for your zone. Lot coverage is the share of your lot that structures are allowed to occupy, commonly capped around 40 to 50 percent in single family zones, and the catch is that your existing house, garage, and hardscape may already use most of that allowance. Floor area ratio, or FAR, limits total building floor area relative to lot size. A FAR of 0.35 on a 10,000 square foot lot means all structures combined cannot exceed 3,500 square feet, existing plus proposed. Height limits cap how tall the structure can be and often rise or fall depending on how far it sits from property lines.
Run these four against your lot and you get your buildable area, the actual envelope inside which a new structure can legally sit, after setbacks, coverage, FAR, and height are all satisfied at once.
Step 3: Check what the map does not show, the easements and restrictions
This is the step that catches the most owners, because the limits are invisible on a satellite image. An easement is a recorded right that someone else, often a utility, holds over part of your land, and you generally cannot build over it. A drainage or utility easement running along your rear lot line can erase the exact area where an ADU would otherwise fit.
Two more private layers can override the city entirely. Recorded deed restrictions and HOA covenants can prohibit accessory structures or rentals even when zoning permits them, and in many jurisdictions these private restrictions are enforced over municipal zoning. Pull your deed and any HOA documents and read them before you design. If your parcel sits in a flood zone, a historic district, or a special overlay, additional rules and approvals can apply on top of base zoning, and overlays in particular can quietly reshape what and where you are allowed to build.
Step 4: Confirm utilities and site realities
A new dwelling needs water, sewer or septic, and electrical service, and capacity is not guaranteed. On public utilities, confirm there is capacity at your meter and line, since some older neighborhoods need an upgrade. On a well and septic, confirm the system can handle the added demand, which is often its own permit and a real cost. These are not zoning questions, but they are make or break feasibility questions, and they belong in the same early check.
Why doing this first saves you the most money
Notice that every expensive mistake in this process happens after someone assumed instead of checked. Paying for a full design before confirming the buildable envelope is how owners end up redrawing plans, restarting the permit clock, or abandoning a project that the lot coverage cap or an easement never allowed. The zoning check is the cheapest step in the entire project, and it is the one that protects every dollar spent after it.
It is also worth being honest about the limit of a do it yourself check. You can confirm your district, read the dimensional standards, and spot obvious dealbreakers in about an hour. What is harder is reconciling all the rules at once, catching the overlay or code nuance that is not obvious, and translating "allowed" into a precise buildable envelope you can actually design to. That reconciliation is where a professional check earns its keep, because it converts a pile of separate rules into a clear yes, no, or here is exactly what fits.
Know what your parcel allows before you spend
The throughline is simple. Buildability is decided at the parcel, before design, by the combination of zoning, dimensions, existing conditions, and recorded restrictions. Confirm it first and everything downstream gets cheaper and faster.
That is the work to front load. A zoning and code research report pulls your district, dimensional standards, overlays, and restrictions into one clear answer of what your specific parcel allows. If you are buying, a pre purchase property assessment tells you what a lot can support before you close, and a feasibility study tests your actual project against the buildable envelope and site realities. When you are ready to move toward permitting, a permit pathway analysis maps the approvals your project will need.
Get a zoning and code research report and know exactly what your parcel allows. One check now tells you what you can build before you spend a dime on design.
Frequently asked questions
How do I check if I can build an ADU on my property? Find your parcel number, look up your zoning district on your city or county zoning map, and read the zoning ordinance to confirm an ADU is an allowed use. Then check setbacks, lot coverage, FAR, and height to see what fits, and review your deed and HOA documents for private restrictions.
What is the difference between zoning and a deed restriction? Zoning is the public rule set by your local government for your district. A deed restriction or HOA covenant is a private rule recorded against your property. Both can limit what you build, and private restrictions are often enforced over zoning, so a green light from the city does not override them.
What is buildable area? It is the actual envelope on your lot where a new structure can legally sit, after applying setbacks, lot coverage limits, FAR, and height rules together, and after excluding easements. It is usually much smaller than the lot itself.
Can I build an addition if my lot is already near its coverage limit? Maybe not. Lot coverage and FAR count existing structures, so if your home, garage, and hardscape already use most of the allowance, there may be little room left for an addition. This is exactly why you check the numbers before designing.
Do I need a survey to check zoning? You can do an initial check from public records without one, but a professional survey gives the exact property lines, easements, and existing conditions needed to confirm the buildable envelope before design and permitting.