Billing
Splitting shared costs fairly: by share, area, flat or metered use
How to split shared costs in a housing association by ownership share, floor area, per flat or metered use, with a worked example comparing all four.
4 min read
No cost split is fair to everyone. The couple in the 95 m² flat think it is unfair to pay more for water than the family of five in 72 m². The ground-floor owner thinks it is unfair to pay for a lift they never use. Every key has winners and losers. The board's job is to pick keys that match how each cost behaves, that it can defend at a meeting, and that residents can follow on their invoice.
Your bylaws may already settle some of this, and changing how costs are split usually needs more than a simple majority. Check before you redesign anything.
The four common keys
Ownership share splits a cost by each flat's share of the association or company, usually fixed when the building was formed. It is stable and often written into the bylaws, but shares set decades ago don't always track size or value today.
Floor area splits by square metres. It is easy to explain and to check, and it roughly reflects how much of the building each flat takes up. It is the most common key for costs that relate to the building as a whole.
Per flat splits equally. It suits costs each household causes in about the same measure whatever its size, such as a broadband or TV contract priced per connection.
Metered use splits by what each flat actually consumes, measured by its own meter. It is the fairest key for costs that depend on behaviour, like water, and it tends to change behaviour too: associations that start billing hot water by meter commonly see consumption fall.
A worked example
Take a four-flat building with a single €1,800 water bill for the half year, and split it each of the four ways.
| Flat | Size · share · use | By share | By area | Per flat | Metered |
|---|---|---|---|---|---|
| A | 35 m² · 15% · 9 m³ | €270 | €242 | €450 | €270 |
| B | 58 m² · 22% · 14 m³ | €396 | €402 | €450 | €420 |
| C | 72 m² · 28% · 22 m³ | €504 | €498 | €450 | €660 |
| D | 95 m² · 35% · 15 m³ | €630 | €658 | €450 | €450 |
Flat D, the largest, pays €630 or €658 when the bill follows size, but only €450 by meter, because two people live there. Flat C, the family of five, pays about €500 by size and €660 by meter. Flat A happens to pay the same by share and by meter, which is coincidence. Per flat ignores both size and use, and charges the studio as much as the four-room flat.
None of these numbers is wrong. They answer different questions about what fair means, and residents will pick the answer that suits them unless the board explains why it chose the one it did.
Match the key to how the cost behaves
The test is simple: what makes this cost go up? Stairwell and outdoor cleaning, insurance, property tax and building maintenance grow with the size of the building, so floor area or ownership share fits. Water, and heating where it is metered per flat, grows with use, so the meter fits. Waste collection is a judgement call: larger households produce more, but bin sizes and emptying schedules are set for the whole building, so many associations split waste per flat. Broadband and TV priced per connection belong per flat.
Where there is no meter, floor area is usually the next best stand-in for water and heat. It is imperfect, but it is much easier to defend than charging every flat the same.
Mixing keys on one cost
Some associations split a single cost two ways: a fixed part by area or per flat, and a variable part by meter. The water company's fixed connection fee is shared per flat, while the price per cubic metre follows each meter. This is closer to how the supplier actually bills the building, and it softens the jump for large households when you switch from area to meter. It does mean two lines on the invoice, which is fine as long as each one shows its calculation.
Changing a key without a revolt
Changing a key moves money between neighbours, so someone always pays more. Do the arithmetic for every flat before proposing anything, and show the effect in euros per month for typical flats: “studio €6 less, three rooms €4 more”. Check what majority your bylaws require. Where a change increases what particular members pay, the rules in some countries ask for a qualified majority or even the consent of those affected.
Consider a transition, half the change this year and the rest next year, and start it at the beginning of a billing period so nobody's invoice mixes two methods. Then explain it once in a notice and again on the first invoice where it applies.
Kelvo Nest lets you choose the key for each cost, whether share, area, per flat or meter, and prints the calculation on every invoice line so the split explains itself. Start free with your first building.