A duplex, triplex or small apartment building is bought for its income, and nothing interrupts income like a sewer backup that puts a unit out of service. Multi-family buildings also load their drains harder than a single house, with several kitchens and bathrooms on a lateral that may be the same age and size as a single-family line next door. The sewer scope on an income property has more to cover and more riding on it.
Quick answer: establish how many laterals the building has and where each enters; scope each one from its cleanout to the main; scope the shared building drain and the base of each stack; inspect the ground-floor and basement unit floor drains, which take the backups; arrange tenant access in advance; and budget drainage repairs into the offer as you would a roof. Multi-family drains fail from grease and overload more than from roots, and the camera shows which.
How many laterals
A converted house usually has one lateral. A purpose-built duplex may have one or two. A small apartment building may have one for the whole building or several. Utility records, the cleanouts in the basement and the camera with a sonde establish the answer, and each lateral is a separate inspection. A building with one lateral for six units has a single point of failure.
The shared building drain
Inside the building, the stacks from each unit join a horizontal drain under the basement or crawlspace floor, and that drain carries everything to the lateral. In an old building it is cast iron, and the camera looks for channeling, scale, cracked hubs and bellies. This is the pipe that, when it blocks, backs up into the lowest unit. See cameras for cast iron and cast iron vs PVC on camera.
Grease
Several kitchens on one drain means grease, and grease is the most common finding in multi-family drainage. The camera shows it as pale build-up on the walls narrowing the bore, heaviest downstream of the kitchen branches. A building with heavy grease needs jetting and a tenant education programme; one where the grease has become a blockage history needs a budget. Grease line inspection is written for commercial kitchens but the picture is the same.
Floor drains and the lowest unit
A basement or ground-floor unit with a floor drain is where the building drain’s backups appear. Camera the floor drain and its branch, ask that tenant directly about backups, and look for the tide marks and replaced flooring that a backup leaves. Reading a floor drain backup shows what to look for.
Tenant access
Scoping a multi-family building means entering occupied units for toilet pulls or branch access, and notice is required by lease and by law in most places. Arrange it through the seller before the inspection date, in writing, and be prepared for a unit to be unavailable. A scope that could not enter one unit should say so.
Each stack
Each stack serves a column of units and rusts at its base. Camera from the cleanout at the base of each, or from the roof, and record the condition. A stack replacement in an occupied building is disruptive and expensive, and a buyer should know which stacks are near it.
What the findings mean for the offer
Drainage on a multi-family building is a capital item like the roof, and the offer should price it. A sound building drain and laterals with normal grease are maintenance: an annual jet and a line in the operating budget. Channeled cast iron or a failing lateral is a capital project: get a quote from the footage and negotiate it as you would any major system. Negotiating sewer repairs covers the process and what drives repair costs the numbers.
Seller records
Ask for plumbing invoices for the past several years. A pattern of drain cleaning calls to one unit or one stack is a camera finding waiting to be confirmed. A seller who has none either has a sound building or has not kept records; the camera tells which.
Ongoing programme
After purchase, a multi-family building benefits from a scheduled scope and jet, yearly for buildings with grease history, and from cleanouts that are accessible without entering units. How often to inspect covers the schedule.
What to record
The number and location of laterals and cleanouts. Footage of each lateral, the building drain, each stack base and the lowest floor drains, with distances and entry points. Grease and scale severity by location. Tenant reports. The seller’s plumbing invoices. This is the drainage file for the building, and it is what the next buyer will ask for.
Converted houses
A single-family house converted to two or three units is the most common small multi-family purchase and the one with the most drainage surprises. The conversion added kitchens and bathrooms wherever the layout allowed, often with long horizontal branches at shallow slope, unpermitted connections into the stack, and an ejector pit for a basement unit that nobody has serviced. The camera follows each branch to the stack, checks the ejector discharge, and confirms that the original lateral, sized and aged for one kitchen, is coping with three. Ask for the permits for the conversion; where there are none, assume the plumbing was improvised until the camera proves otherwise.
Vacancy and the inspection
A vacant unit is easy to scope and tells less: its branches have been dry and its traps may have emptied. Run water in a vacant unit for a few minutes before scoping so that the branches show their working condition.
Common questions
How many sewer scopes does a duplex need?
One per lateral, plus the shared building drain and each stack base. A converted house is usually one lateral; check.
What is the most common finding in multi-family drains?
Grease from multiple kitchens, followed by cast iron scale and channeling in older buildings.
Can I scope occupied units?
With notice arranged through the seller, yes. Plan it before the inspection date.
Related guides
See condos and townhomes, the complete sewer scope guide, and multi-frequency locators explained.