10-Year Rule for Unlawful Dwellings

Understanding when a building can lawfully be used as a home — particularly if planning permission was never granted — is one of the most misunderstood areas of planning law.

If you have converted a building into a dwelling without permission, subdivided a house into flats, or breached a condition restricting residential occupation, the question of immunity from enforcement may arise.

This article explains:

• The current legal position under section 171B(2) of the Town and Country Planning Act 1990

• How the law changed in April 2024, and

• Key principles

What Is Section 171B(2)?

Section 171B(2) of the Town and Country Planning Act deals with unauthorised changes of use of a building to a single dwellinghouse.

In simple terms:

If a building has been used continuously as a single dwellinghouse for the relevant period, the local planning authority (LPA) may lose the ability to take enforcement action.

The 10-Year Rule (Post-April 2024)

Following reforms introduced by the Levelling-up and Regeneration Act 2023, the time limit for enforcement is now 10 years for changes of use to a dwellinghouse.

Before 25 April 2024, the period was four years.

Transitional Provisions

The old four-year rule still applies if:

• The change of use to a dwellinghouse occurred before 25 April 2024, and

• The relevant four-year period had already accrued or was running under the transitional arrangements.

This makes identifying the precise date of breach critically important.

When Does Section 171B(2) Apply?

Section 171B(2) applies where there has been a material change of use (MCU) of a building to use as a single dwellinghouse

It also applies where a planning condition prevents residential occupation and that condition is breached. This was confirmed in FSS v Arun DC & Brown [2006] EWCA Civ 1172.

Importantly, the planning condition does not need to expressly say “no residential use.” If its effect prevents occupation as an independent dwelling, the section may apply.

What Is a “Single Dwellinghouse”?

This is not always straightforward.

In Moore v Secretary of State [1998] JPL 877, the court said the distinctive characteristics of a dwellinghouse are its ability to afford the facilities required for day-to-day private domestic existence.

In practical terms, that usually means:

• Sleeping facilities

• Cooking facilities

• Washing facilities

• A degree of privacy and independence

Each case turns on fact and degree.

Subdivision Into Flats

Following April 2024 reforms, section 171B(2) also applies to:

• The subdivision of a single dwelling into flats

• Changes involving parts of buildings

The word “building” includes part of a building (section 336 TCPA 1990), and flats are treated as dwellinghouses.

In Van Dyck v SSE; Doncaster MBC v SSE [1993] JPL 565, the Court of Appeal confirmed that the immunity provisions apply to subdivision into separate dwellinghouses.

Each self-contained flat can potentially benefit from the 10-year rule individually.

When Section 171B(2) Does Not Apply

(a) HMOs

The section does not apply to changes of use to Houses in Multiple Occupation (HMOs) where units are not self-contained.

Even if the use falls within Class C4, there has not been a change of use to a “single dwellinghouse.” In those cases, the general 10-year rule under section 171B(3) applies instead.

This distinction can be crucial.

(b) Buildings Unlawfully Constructed as Dwellings From the Outset

A particularly important limitation was clarified by the Supreme Court in Welwyn Hatfield BC v SSCLG & Beesley. In that case:

• Permission was granted for a barn

• The building was constructed to resemble a barn

• It was built and used as a dwelling from the outset

The Supreme Court held that section 171B(2) was not apt to cover this situation because there had been no change of use — the building was used as a dwelling from the moment it came into existence.

Lord Mance emphasised that “use” in the section refers to real, material use — not merely a departure from permitted use.

The implication is significant:

If a building was unlawfully built and always used as a dwelling, immunity may fall under section 171B(3), not section 171B(2).

Identifying the Date of Breach

To rely on immunity, two questions must be answered:

1. When did the change of use occur?

2. Did the use continue throughout the required period?

When Did the Change Happen?

The courts have made clear that neither physical works nor occupation alone are decisive.

In Impey v SSE and Backer v SSE [1983] JPL 167, the courts held that:

• The physical state of the building is important but not decisive

• Actual use is important but not decisive

• The matter must be assessed “in the round”

A building may be capable of being used as a dwelling before someone physically moves in.

However, mere camping or sleeping occasionally in a building does not automatically make it a dwellinghouse. In Backer, the court said that sleeping and eating in premises does not make them a dwellinghouse.

Evidence matters in such cases. This may include:

• Utility bills

• Council tax records

• Tenancy agreements

• Marketing particulars

• Witness statements

• The physical layout

The Requirement for Continuous Use

Even if a change of use occurred more than 10 years ago, the use must have been continuous. This principle was established in the courts when the Court of Appeal held that immunity only arises if the use continues throughout the relevant period such that enforcement action could have been taken at any time.

If the use stops, the “clock” resets.

To become lawful, residential use must be affirmatively established over the relevant period.

What About Vacant Periods?

Short gaps between occupiers are not necessarily fatal.

In Basingstoke and Deane BC v SSCLG & Stockdale, refurbishment and marketing during a vacancy did not break continuity because enforcement could still have succeeded during that period.

However, a significant break, removal of residential facilities, reversion to another use, may restart the clock.

Each case turns on fact and degree.

Common Pitfalls

1. Assuming Time Automatically Makes It Lawful

Time only assists if the use was:

• A material change of use

• Continuous

• Within the correct statutory category

Many claims fail because one of these elements is missing.

2. Confusing Physical Works With Use

Installing kitchens and bathrooms does not automatically establish a change of use.

The courts repeatedly emphasise that actual or intended use must be assessed objectively.

3. Ignoring Planning Conditions

A breach of an occupancy condition may fall within section 171B(2). Owners often overlook conditions attached decades ago.

4. HMO Confusion

Many assume any residential use benefits from the same rule. It does not. HMOs fall into a different category.

5. Gaps in Occupation

Periods of vacancy can be fatal if they are significant. Evidence of continuous occupation must be robust.

6. Enforcement Notice Drafting Issues

LPAs sometimes struggle where a building was used as a dwelling from the outset without a change of use.

If there was no “development” as defined by statute, enforcement can become procedurally complex — but this is highly technical territory.

Why This Matters

The consequences are serious:

• An enforcement notice may require cessation of residential use

• Mortgageability may be affected

• Sales can collapse

• Insurance risks arise

• Criminal liability can follow non-compliance

Equally, properly established immunity can:

• Secure significant land value

• Enable refinancing

• Provide certainty

• Support lawful development certificate (LDC) applications

The financial implications are often substantial.

The Importance of Evidence

Immunity cases are evidence-heavy.

Local planning authorities and Inspectors will scrutinise:

• Electoral roll entries

• GP registration

• Bank statements

• Delivery records

• Utility consumption patterns

• Witness credibility

Assertions without documentation are rarely persuasive.

The burden of proof rests on the applicant, on the balance of probabilities.

Final Thoughts on the 10-Year Rule

Change of use immunity cases are legally complex and highly fact-sensitive. The interaction between:

• Section 171B(2)

• Section 171B(3)

• Planning conditions

• Subdivision

• Unlawful construction

• The 2024 reforms

means that assumptions can be dangerous.

A small factual misunderstanding — such as misidentifying the date of breach or overlooking a break in occupation — can undermine an otherwise strong case.

If you believe a building may have acquired immunity from enforcement, or if you have received correspondence from the council, it is essential to obtain specialist planning advice.

About me

Andrew Ransome is the planning director at ADP and is a chartered member of the RTPI, with over 22 years of town planning experience.

Andrew has extensive experience offering strategic planning solutions to challenging projects in both rural and urban settings. Follow him on Linkedin.

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