Splitting a house into flats: what happens to your council tax 2026

When a terraced house is converted into three self-contained flats, or three flats are knocked through into one family home, the resulting council tax bill is not simply the old bill multiplied or divided. The Valuation Office Agency (VOA) treats each self-contained unit as a separate dwelling for council tax purposes, so splitting or merging a property changes how many bills exist in the first place, not just how big each one is.

How the VOA decides what counts as one home

Council tax is charged per "dwelling", a term defined in the Local Government Finance Act 1992. In practice the VOA's test is whether a part of a building is a self-contained unit: does it have its own means of access, and could it be lived in on its own, with its own kitchen and bathroom facilities? If the answer is yes, the VOA treats it as a separate dwelling with its own entry in the council tax valuation list and its own band, regardless of who owns it or whether it has ever been sold separately.

That is why converting a house into flats, or merging flats back into one home, triggers a VOA review under the valuation list alteration rules in section 24 of the 1992 Act. The review happens when the physical change is complete, not when a flat is later bought or sold.

Splitting a house: more dwellings, not a bigger bill split three ways

When a single house is divided into self-contained flats, the VOA deletes the one entry for the house and creates a new entry, with its own band, for each flat. Each flat's band is assessed independently, based on what it would have been worth at 1991 prices as a stand-alone self-contained unit, not as a fraction of the original house's value.

That independent assessment is the detail that catches people out. A smaller flat does not automatically inherit a proportionally smaller band. In practice, converted flats in an already-banded house often land in a similar lower band to each other because they share a similar size and specification, but there is no fixed rule that guarantees this, and the VOA can band each unit differently if their layouts differ.

Worked example. Take a house currently in Band E, paying the 2026-27 national average Band E bill of £2,946.74 a year. If it is converted into three broadly similar self-contained flats and the VOA bands each one at Band B, the new combined bill is three separate Band B bills: £1,875.20 x 3 = £5,625.60 a year, against £2,946.74 before conversion. The total liability for the building nearly doubles, even though no single flat is individually expensive to run.

Merging flats: fewer dwellings, one combined band

The same mechanism runs in reverse. Where two or more self-contained flats are knocked through into one home, with the separate kitchens, bathrooms or external access points removed so the result functions as a single dwelling, the VOA deletes the separate entries and creates one new entry for the combined property. That single entry is banded on the combined property as it now stands, again assessed independently rather than by adding the old bands together.

Using the same figures in reverse: three Band B flats paying £1,875.20 each (£5,625.60 total) that are merged into one home banded at Band E would move to a single £2,946.74 bill, a reduction of roughly 48% in the combined liability. The direction of the change depends entirely on how the VOA bands the resulting dwelling, not on a simple rule that merging always costs less or splitting always costs more.

The full 2026-27 band table

These are the national average council tax figures for 2026-27, averaged across 296 English local authorities, shown against the standard band ratios set out in the 1992 Act:

Actual bills vary sharply by local authority even within the same band. For context, a Band D bill in Wandsworth is £1,028.21 for 2026-27, against £2,765.02 in Dorset, a gap of more than £1,700 a year on an identical band, before any splitting or merging is considered.

Why this question keeps coming up for flat conversions

Conversions matter because flats are a meaningful and growing slice of the housing stock behind this kind of split. In 2025, flats accounted for roughly 16% of the 795,000-plus residential sales recorded by HM Land Registry, and of those flats, close to 98% were sold leasehold rather than freehold, reflecting how commonly a single freehold building has been carved into separately-owned, separately-let units. Each leasehold flat created this way gets its own valuation list entry on exactly the same self-contained-unit basis described above.

What to check before converting or merging a property

Physically creating or removing a self-contained unit usually needs planning permission and building regulations sign-off in its own right, separate from the council tax question covered here. Once the building work is complete, the property owner, or the local authority acting on information such as a planning or building control record, notifies the VOA so the valuation list can be updated. Owners who are unsure whether a proposed conversion will be treated as one dwelling or several can ask the VOA directly before committing to the work, and can later challenge a new band through the normal council tax band appeal process if they think it has been assessed incorrectly.

This is general information about how council tax bands are assessed, not advice on a specific property or project. Speak to a qualified adviser, or contact the Valuation Office Agency directly, before relying on it for a conversion or merger you are planning.

Figures are based on 2026-27 council tax rates across 296 English local authorities and HM Land Registry's 2025 residential transaction data; see the full council tax band guide for how the band system works, the extension and reassessment guide for what happens when a home is enlarged rather than divided, and the leasehold and freehold guide for how flat ownership typically works once a conversion is complete. Browse more buyer guides, or try the true cost tool on a property of your own.