The Wall Between Two Units

Wednesday, October 28th, 2026 — The water heater in unit 3B let go on a Sunday night. The owner was out of town. By Monday morning the ceiling of 2B was sagging over the dining table, the hallway carpet in 2B was dark along the wall the two units share with the corridor, and the building manager had a key to 3B and a restoration company already in the elevator. Three people called three carriers before lunch. The owner of 3B called the carrier on her unit-owners policy. The owner of 2B, who rents the unit out, called the carrier on his landlord policy and told his tenant to call hers. The association called the carrier on the master policy. All three notices described the same water, and all three callers used the word mold by the end of the week, because the ceiling paper in 2B spotted before anyone opened it.

A house claim has one policy and one insured. This one has a declaration, a master policy, at least two unit policies, and sometimes a renter's policy, and the mold follows the water across all of them. The adjuster who treats it as a house claim will pay the wrong things and miss the right recovery. The first job is to find out which contract owns which square foot, and to do it before the colony in the shared wall gets any older.

Read the declaration before you price anything

The association's declaration, sometimes called the covenants or the CC&Rs, plus the master policy's form, decides what the association insures. Adjusters and association managers use three shorthand names for that choice. They are not ISO form numbers. They are descriptions of how far the master policy reaches into the unit, and the declaration is the document that picks one.

• Bare walls, sometimes called studs out. The master policy covers the structure out to the unfinished drywall or the studs. Paint, wallpaper, flooring, cabinets, fixtures, and anything the unit owner installed are the unit owner's problem. A spotted ceiling face in 2B is not a master-policy claim. The wet joists above that ceiling may be.

• Single entity, sometimes called walls in. The master policy covers the building as it was originally sold, including the original paint, cabinets, and fixtures. Improvements the current owner added, a kitchen remodeled in 2019, an upgraded floor, are the unit owner's.

• All in. The master policy is written to include the unit's improvements and betterments. The unit-owners policy then carries less building coverage and more of the loss-assessment and liability load. Confirm this in the form. "All in" said aloud in a board meeting is not the same thing as "all in" written on the declarations page.

Ask the manager for the declaration pages that define the unit boundaries, and for the master policy's declarations and the insuring agreement. Do not accept a one-word answer from the board president. The water does not care which version is convenient. If the documents are slow to arrive, photograph and meter everything, open what you are allowed to open, and hold the coverage letter until you have read them. A payment made on the wrong policy is hard to get back, and it can waive a subrogation claim the carrier still wanted.

One floor at a time

Start where the water started. In 3B the failed heater is a sudden discharge from a plumbing system on the unit owner's ISO HO-6, the unit-owners form, if she has one and if the heater is her property under the declaration. The closet floor, the drywall she owns, her belongings, and her additional living expense sit on that policy, subject to its fungi limit for whatever has already colonized. The common pipe and the common wall, if the declaration calls them common elements, sit on the master policy.

Then follow the water down. The ceiling cavity between 3B and 2B is often common element even when the painted face of 2B's ceiling is part of the unit. That split is the whole argument in a bare-walls building. The joists and the backside of the ceiling board can be the association's. The paint, the texture, and the board itself, once it is the unit's interior finish, can be 2B's. Open the ceiling and photograph the boundary the declaration describes. A scope that says "ceiling, 120 square feet" without saying whose ceiling it is will be paid twice or paid by nobody.

The tenant in 2B has an ISO HO-4 if she bought renters insurance. That form covers her personal property and her additional living expense. It does not cover the building, the cabinets, or the floor the landlord owns. Her couch and her hotel nights are the HO-4. The landlord's floor and the inside of his ceiling are his policy, the HO-6 or a landlord form, to the extent the master policy does not pick them up. His loss of rents, if he has that coverage and the unit is unlivable, is his also. Do not put the tenant's hotel on the landlord's file, and do not put his floor on hers.

The corridor wall is the easy one to forget. Water that ran inside the party wall can wet the corridor side, which is almost always a common element. The master policy's adjuster should see it on the first visit. If that adjuster is not you, send the photos the day you take them. A shared cavity that dries on one side and stays wet on the other is how a small release becomes a second colony three weeks later.

Which policy owns the damage

This is the split for a bare-walls building, which is the version that produces the most overlap. A single-entity or all-in master policy pulls some of these items back to the association. Read the declaration, then move the item.

The association's master policy usually covers:

• The joists and the common side of the ceiling cavity.

• The corridor side of the shared wall.

3B's HO-6 usually covers:

• The failed water heater and the unit finishes around it.

• That owner's share of a board assessment for the master-policy deductible, under loss-assessment coverage, up to the limit on the declarations page.

The owner of 2B, not the tenant, usually covers the painted ceiling, the flooring, and the cabinets in that unit. The tenant's HO-4 covers her furniture, clothes, and hotel.

Loss assessment is the coverage unit owners do not know they have. When the association repairs common elements and assesses each owner for the master-policy deductible or for a shortfall, the HO-6's loss-assessment coverage is what responds. The limit is the one printed on that HO-6 declarations page. Owners who never raised it discover the number in a building-wide drying job. Pay only the assessment that comes from a loss the unit policy covers, only up to the limit printed on that declarations page, and only after you have the assessment letter. An owner's request that you "just cover my share" is not an assessment.

Each policy brings its own fungi limit

The fungi give-back does not pool across policies. The owner of 3B may have $10,000 of fungi coverage. The owner of 2B may have $5,000. The master policy may have a fungi limit of its own, or a pollution exclusion that swallows mold in the common elements, or both. The tenant's HO-4 has whatever fungi limit her form gives for her property, which is often the same small number and does not pay to tear out the landlord's ceiling.

Sort each estimate before you apply any cap. Wet carpet padding and a sudden plumbing repair are water damage on the policy that owes them. Colonized paper, containment set up because of growth, and testing are fungi dollars on that same policy, inside that policy's limit. Do not let the master carrier's fungi limit eat the unit owner's water damage, and do not let a unit owner's limit eat common-element demolition. The earlier piece in this series on splitting a single-house invoice applies here once per policy. The new mistake is applying it once for the whole building.

If the master policy excludes fungi outright, the association may still have to repair the common element and then assess the owners. That assessment is a loss-assessment question on each HO-6, not a mold invoice you re-code onto the master file. Say so in writing to the board and to each unit adjuster so the owners hear it before the assessment arrives.

The days the source unit stays locked

The Environmental Protection Agency's guidance to building owners is that mold can begin growing on wet materials within 24 to 48 hours. In a house, the owner is standing there with a key. In a condo, the source unit may be empty, the lockbox code may be with a manager who is on another property, and the owner of 2B cannot legally open 3B to stop the water that is ruining her ceiling. Those hours belong in every file.

Write down when each unit was reached, who controlled the key, and when the water was stopped and the drying equipment was set. A colony that established because 3B was locked until Tuesday is not automatically 2B's failure to mitigate. It may be a fact that matters for subrogation against 3B's owner, or against the association if the declaration required the association to maintain the heater or to provide emergency access. It is a poor reason to deny 2B's own covered water damage.

Get into the cavity as soon as someone with authority will open it. The IICRC water-damage standard, S500, is about drying what got wet. Waiting on a coverage opinion while the joist bay stays wet makes a fungi claim on whichever policy eventually owes the tear-out. Coverage can be sorted on paper. The building cannot.

What you say at the unit door

Unit owners in this situation assume one carrier is in charge and that the other owners are the obstacle. You can correct that without sorting the declaration in the hallway.

The water started in 3B and came through the ceiling into this unit. Your policy and the association's policy cover different parts of that, and I will not know which parts until I have read the declaration. What I can do today is document what is wet, get drying started on what we can reach, and tell you what I need from you. Please do not authorize demolition of the common wall. Please do send me your declarations page and any photos from last night.

Say the same facts to the tenant, with one change. Her policy, if she has an HO-4, is for her belongings and her extra living costs, not for the ceiling. If she does not have a policy, say that plainly and point her to the landlord for the building repairs and to her lease for what the landlord owes her. Do not promise that his insurance will house her. That promise is his coverage and his lease, and you may not have either in front of you.

Subrogation starts on the first visit

The carrier that pays 2B will want to recover from whoever was responsible for the heater and for the delay. That work belongs to the subrogation team later. What belongs to you is the file they can use. Photograph the heater, the failed fitting or tank, and the nameplate. Keep the failed part if you can do it without fighting the association's contractor, or photograph it before it goes down the chute. Record the out-of-town dates, the lockbox, and the hour the water stopped. Name every carrier and every claim number in your notes.

Do not sign a release, and do not let the insured sign one, in exchange for the association "taking care of the ceiling." A release written on a contractor's clipboard can end a recovery that was worth more than the ceiling. Tell the insured to send you anything the board or the other owner asks them to sign.

Tender early. A short letter to 3B's carrier and to the master carrier, with the photos and the date of loss, is enough to put them on notice. You are not trying their liability in that letter. You are telling them a payment is coming and that your file will be offered for review. The recovery article in a later series can pick up from a notice. It cannot pick up from a heater that was hauled away and a release nobody copied.

One building, separate files

Open a file for each policy you adjust, and keep the other policies identified in each one. Pay the rows that are yours. Copy the photos to the adjuster who owns the other rows. When fungi limits differ, show each insured their own limit and their own list of fungi lines, not a blended building total that no single policy owes.

The Monday morning version of this loss is a water heater, a wet ceiling, and a tenant who wants a hotel. The version that arrives in week three is three estimates, two colonies, and a board that has already assessed the owners for a deductible nobody reserved. The declaration, read on day one, is what keeps it the first version.