CIL Existing Building: Floorspace and the Six-in-36 Rule

 

A CIL existing building can reduce the Community Infrastructure Levy bill on a redevelopment, conversion or replacement scheme, but only if the detailed rules are met. The well-known six-in-36 rule is part of the test, not a free-standing credit for every square metre already on the site.

This guide explains which existing floorspace can be brought into the CIL calculation, what counts as an in-use building, how retained and demolished areas are treated, and the evidence you should collect before planning permission is granted or a building disappears.

Where the development is a conversion rather than redevelopment, our CIL change of use guide explains how the same floorspace rules interact with conversions and permitted development.

 

What is a CIL existing building?

 

For the standard CIL calculation, an existing building first has to be a relevant building. Broadly, that means a building situated on the relevant land on the day planning permission first permits the chargeable development.

A building that was demolished before that date cannot normally be brought back into the calculation simply because it used to stand on the site. That is why demolition before the CIL position has been established can be expensive.

If the building is still there, the next question is whether it qualifies as an in-use building. Schedule 1 to the Community Infrastructure Levy Regulations 2010 says that the relevant building must contain a part that has been in lawful use for a continuous period of at least six months within the three years ending on the day planning permission first permits the chargeable development.

 

The six-in-36 rule is a gateway

 

The six-in-36 rule is often shortened to: “use the building for six months and you get all the floorspace back”. That is too simple.

If part of the relevant building satisfies the continuous lawful-use test, the building can qualify as an in-use building. You must then apply the Schedule 1 calculation to identify the retained and demolished parts which can actually reduce the net chargeable area.

That distinction matters on larger sites, mixed-use buildings and schemes where some floorspace is retained while other parts are demolished. Passing the in-use test does not remove the need to establish what the qualifying floorspace is and where it sits in the statutory formula.

 

Lawful use means actual use

 

A lawful planning use is not enough by itself. The building, or part of it, must actually have been used for that lawful use during the qualifying period.

In R (Hourhope Ltd) v Shropshire Council [2015] EWHC 518 (Admin), the High Court rejected the idea that a lawful use which could have been carried on was sufficient. The factual use of the building mattered.

The later High Court decisions in R (Segrue Investments Ltd) v Swindon Borough Council [2026] EWHC 2080 (Admin) and R (Herod Property Ltd) v Westminster City Council [2026] EWHC 2122 (Admin) underline the importance of proving the position rather than assuming that the collecting authority will accept it.

 

What evidence should you keep?

 

The Regulations allow a collecting authority to disregard an in-use claim where it does not have sufficient information, or information of sufficient quality, to establish the relevant facts. The safest approach is therefore to assemble the evidence before you need it.

Useful evidence can include:

• dated leases, licences or tenancy records
• business rates or council tax records
• utility bills showing genuine occupation and activity
• bank records or rent evidence where appropriate
• dated photographs of the building in use
• statements from occupiers, agents or other people with direct knowledge
• measured surveys and floor plans
• approved planning drawings showing the existing building and its floor levels

No single document automatically proves six months of continuous lawful use. The evidence should make the actual activity, the dates and the lawful planning use clear.

 

Segrue: late evidence and revised liability notices

 

Segrue Investments concerned a former bank being converted to residential use. The collecting authority initially decided that the evidence was not sufficient to establish the in-use building test, and liability notices were issued without the existing-building deduction.

The case is particularly useful because the dispute did not end with the six-month test. The High Court treated the regulation 113 review and regulation 114 appeal machinery as an adequate alternative remedy and rejected the attempt to use regulation 65 as a general late-review route after those deadlines had expired. Better evidence produced later could not simply sidestep the statutory timetable.

The practical lesson is not that you can safely miss the statutory review deadline and sort the evidence out later. It is the opposite: make the evidential case early and use the formal review and appeal route within time if the authority disagrees.

 

Herod: do not assume that your CIL calculation is zero

 

Herod Property involved a Class MA conversion where the developer believed retained in-use floorspace reduced CIL to zero. The High Court accepted that the regulations allow a developer to form its own view about whether the zero-CIL exception applies, but warned of the risks of starting work without first resolving the point with the collecting authority.

The collecting authority is not bound by the developer’s own calculation. If the authority lacks sufficient information, Schedule 1 contains deeming powers which can work against the developer. More importantly, starting the development can remove the ordinary chargeable-amount review and appeal routes.

If a zero calculation depends on an existing-building deduction, the cautious route is to put the plans and evidence before the collecting authority and resolve any disagreement before commencement.

 

Gross internal area comes first

 

Before an area can reduce the CIL calculation, you need to know whether it is gross internal area, usually shortened to GIA. The CIL Regulations do not define GIA. Government guidance says the Valuation Office Agency normally uses the RICS Code of Measuring Practice when deciding CIL appeals.

This matters with garages, storage areas, plant space and especially lofts. A roof space is not automatically GIA simply because it is boarded or used for household storage.

Our analysis of CIL Appeal 1891221 explains a 2026 VOA decision where one loft area with permanent stair access was accepted while three hatch-accessed areas were not accepted on the evidence.

 

Retained floorspace and demolition credit

 

Schedule 1 treats retained and demolished floorspace differently within the formula. In-use parts that are retained can form part of the KR deduction, while qualifying in-use parts that are demolished before completion can form part of E.

There is also a narrower route for retained parts of some other relevant buildings which are not in-use buildings, where the intended use after completion could lawfully and permanently have been carried on without a new planning permission immediately before the first-permits date.

This is why a proper CIL calculation is more than subtracting the old building area from the new building area.

 

Do not demolish the evidence

 

If demolition is proposed, record the building before work begins. Once the structure has gone, arguments about floor levels, GIA, access, occupation and actual use become much harder to prove.

A measured survey, dated photographs, floor plans and occupation records should be assembled before demolition where the existing-building deduction may matter.

 

What if the council rejects the deduction?

 

If you think the chargeable amount is wrong, the statutory route starts with a written review request under regulation 113. It must normally be made within 28 days beginning with the day the liability notice was issued.

If the review does not resolve the problem, a regulation 114 appeal to the Valuation Office Agency must normally be made within 60 days beginning with the day the original liability notice was issued. The 60-day clock does not restart when the review decision arrives.

Do not commence development while relying on those routes. Commencement can prevent a review or appeal being made, or cause one already under way to lapse. Our CIL appeals guide explains the deadlines in full.

If the underlying planning application itself is refused, that is a separate planning matter and can usually be challenged through the normal planning appeal system.

 

Costs and the planning application

 

The existing-building deduction is part of the CIL calculation rather than a separate planning application. Any planning application fee is separate from CIL and depends on the application being made. See our planning application fees guide.

 

Relevant CIL rules and guidance

 

• Community Infrastructure Levy Regulations 2010, regulation 40
• Schedule 1: chargeable amount
• Government CIL guidance on calculating liability
• Valuation Office Agency CIL manual on chargeable-amount appeals

Community Infrastructure Levy (CIL)

 

CIL Existing Building Page Updated: 4th September 2026