Who maintains what in a duplex?

"Whose job is the roof?" is one of the most common questions duplex owners ask. The answer depends on two things: what your strata plan says, and whether you've made a by-law that changes the default rules.

Step 1 — your strata plan decides what's shared

Every strata plan shows where each lot ends and the common property (the shared part) begins.

• In many attached duplexes, the boundary is the inside face of the walls, floors and ceilings. That makes the roof, outside walls, shared wall and slab common property, owned by both of you through the owners corporation.
• In many newer two-lot schemes, especially separate houses, the lots are drawn around the land itself. Each house is part of its own lot, and the only common property might be a shared driveway, fence line or garden.

If you're not sure which you have, the registered strata plan will tell you. We can get a copy at cost if neither of you has one.

Step 2 — the default rule

• Common property: the owners corporation (both owners together) must keep it in good repair and replace it when needed. That's section 106 of the *Strata Schemes Management Act 2015*. Costs are shared by unit entitlement, which for most duplexes means 50/50.
• Your lot: you look after it yourself, at your own cost.

So if the roof is common property and it leaks over your neighbour's side, it's still a shared cost, even though only one home is affected.

Step 3 — making each owner responsible for their own side

Many duplex owners would rather each look after "their half": their own roof, walls, windows and gutters. The law allows this through a by-law (sometimes called a common property rights or maintenance by-law). It sets out which parts of the common property each owner maintains, at their own cost.

To make one:

1. Agree the wording with your neighbour. A solicitor usually drafts it so it covers the right parts clearly.
2. Both owners approve it. Today that's a special resolution at a general meeting, which in a 50/50 duplex means you both agree. Under the new small strata scheme rules, when they start, it will be a written resolution signed by both owners.
3. Register it with NSW Land Registry Services. A by-law has no effect until it's registered.

Even with a by-law in place, the building insurance stays in the owners corporation's name (unless your homes are detached and you've both agreed to insure separately), and the owners corporation can still step in if work isn't done.

What we can do

Duplex Strata handles the paperwork for $95 + GST per by-law for our administration. The solicitor's drafting and the Land Registry fee are extra, at cost, and we'll tell you the total before anything starts.

Can one owner just decide to fix their side of the roof?

They can repair their own lot. If the roof is common property, the work is a decision for both owners, unless a registered by-law already makes that owner responsible for it. Put any agreement in writing first.

Our duplex is two separate houses. Do we need a by-law?

Often not. If your strata plan already puts each house inside its own lot, each owner already maintains their own home. The by-law matters most for attached duplexes where the structure is common property.

What if my neighbour won't agree to a by-law?

A by-law needs both of you. If you can't agree, see our guide on what to do when a neighbour won't cooperate.

Does a maintenance by-law change who pays the insurance?

No. Building insurance is still arranged and paid by the owners corporation and shared by unit entitlement, unless detached homes have validly opted out.