Short answer: if a fixture in your kitchen discharges fats, oils, or grease — a pot sink, prerinse sink, wok station, or the floor drains a kettle empties into — the plumbing code requires it to run through a grease interceptor or automatic grease removal device. It is the plumbing code, not the health code, that actually mandates this, and a private home kitchen is explicitly exempt. On a used space, whether a properly sized interceptor already exists is a five-figure question you want answered before you sign.
When an interceptor is required
The 2021 International Plumbing Code §1003.3.1 sets the trigger by what the fixture discharges, and names restaurants directly:
"A grease interceptor or automatic grease removal device shall be required to receive the drainage from fixtures and equipment with grease-laden waste located in food preparation areas, such as in restaurants, hotel kitchens, hospitals, school kitchens, bars, factory cafeterias and clubs." — 2021 IPC §1003.3.1
And it draws the line at the home kitchen — which is exactly why a residential setup never needed one and a commercial one always does:
"A grease interceptor or an automatic grease removal device shall not be required for individual dwelling units or any private living quarters." — 2021 IPC §1003.3.4
How it’s sized: the 30-minute rule
Interceptors are not one-size. A gravity grease interceptor is sized off your peak flow and a fixed retention time:
"The required capacity of gravity grease interceptors … shall be determined by multiplying the peak drain flow into the interceptor in gallons per minute by a retention time of 30 minutes." — 2021 IPC §1003.3.7
Hydromechanical (smaller, under-sink) units are instead sized off a flow-rate/retention-capacity table (IPC Table 1003.3.5.1). The practical point for a buyer: an interceptor that was sized for the previous tenant’s smaller line may be undersized for what you plan to run, and up-sizing means plumbing work, not a swap.
The health-code backstop: it has to be cleanable
Where the plumbing code decides whether you need one, the FDA Food Code adds a placement rule so it can actually be maintained. §5-402.12:
"If used, a grease trap shall be located to be easily accessible for cleaning." — FDA Food Code 2022, §5-402.12
An interceptor buried under new equipment or behind a wall — a common "saved money on the build" shortcut in a used space — is both a plumbing and a health-code problem, and a maintenance nightmare that leads to backups.
What to check before you buy a space
- Is there an interceptor at all, and is it sized for your planned peak flow (not the last tenant’s)?
- Is it accessible for cleaning, per the FDA rule — or is it buried?
- Local rules override. Many jurisdictions use the Uniform Plumbing Code (UPC) instead of the IPC, and cities set their own interceptor sizing and pump-out schedules through the sewer authority. Confirm the local requirement before you build.
The grease-producing appliances that drive this are the same ones that force a Type I hood — see Type I or Type II hood? — and the sinks an inspector requires are in the sink and dish-machine guide. Price the equipment against its documented failure modes: browse the model records.
IPC §1003 text from the 2021 International Plumbing Code via ICC Digital Codes; the FDA quote is from the FDA Food Code 2022. Codes are adopted and amended locally (and many jurisdictions use the UPC) — confirm your jurisdiction’s current requirement. General information, not code-compliance or legal advice.