CIL Extension Exemption: Residential Extensions Explained

 

The CIL extension exemption can remove Community Infrastructure Levy from a qualifying extension to your main home. It is mainly important where an extension creates 100 m² or more of new floorspace, because smaller extensions that do not create a new dwelling are usually already covered by the minor development exemption.

The extension exemption is different from the residential annexe exemption and the whole-house self-build exemption. It has its own claim form, it does not require a Commencement Notice once granted, and it does not carry the annexe’s three-year clawback period.

 

When does the CIL extension exemption apply?

 

Regulation 42A of the Community Infrastructure Levy Regulations 2010 sets the basic test. The person claiming the exemption must own a material interest in the main dwelling and occupy that dwelling as their sole or main residence.

The development must then be a residential extension. For CIL this means an enlargement to the main dwelling which does not comprise a new dwelling.

Those points matter. An extension to a property you own but do not occupy as your main home does not qualify under this exemption. Nor can the extension exemption be used for works which actually create a separate new dwelling.

 

Extensions below 100 m² are usually already exempt

 

Regulation 42 provides a separate minor development exemption where the new-build floorspace is less than 100 m², unless the chargeable development comprises one or more dwellings.

That means an ordinary house extension below 100 m² which does not create a new dwelling will normally fall outside any CIL payment without needing the specific residential extension exemption.

The specific extension exemption becomes particularly important for larger home extensions of 100 m² or more. There is no upper size limit in regulation 42A itself, but the extension still has to be an enlargement to the claimant’s main dwelling and must not comprise a new dwelling.

 

Form 9 must be dealt with before work starts

 

If the specific exemption is needed, the claim must reach the collecting authority before the chargeable development commences. The current form is Form 9: Residential Extension Exemption Claim.

A valid claim also needs the information and documents required by the form. Regulation 42B requires the collecting authority to grant the exemption and notify the claimant once it has received a valid claim.

Do not start simply because the form has been sent. Government guidance says the exemption must be obtained before development commences. If the project is already close to starting, make sure the authority has dealt with the claim first.

Our CIL forms guide explains the other forms which may be relevant to the project.

 

No Commencement Notice is required for the exempt extension

 

This is an important difference from an annexe or a self-build home. Regulation 67(1A) says the Commencement Notice requirement does not apply where no CIL is payable because a residential extension exemption has been granted.

So, once the qualifying extension exemption has been granted, you do not need to submit Form 6 merely for that exempt extension.

Do not apply that rule too broadly. If the development includes other chargeable elements, or the scheme changes so that the exemption no longer covers the development, the CIL position needs to be reconsidered before work continues.

 

There is no three-year extension clawback

 

The three-year CIL clawback in regulation 42C applies to residential annexes, not residential extensions. A qualifying extension therefore does not acquire the annexe rules about letting or selling a separate unit within three years.

That does not mean later changes to the planning permission are irrelevant. If the development itself changes, the authority may have to recalculate CIL and a further exemption claim may be needed.

 

What if the extension changes under section 73?

 

A later section 73 permission can alter the CIL calculation. Where development which already benefited from a self-build, annexe or residential extension exemption is amended by a section 73 permission and that change creates a new CIL liability, the government provides Form 13: Further Exemption Claim.

Do not assume the first exemption simply covers any larger or different scheme. The section 73 permission is assessed under the amended-permission rules in Schedule 1, and any further exemption should be dealt with before the altered development creates a problem.

 

Retrospective permission is a serious CIL risk

 

Government guidance is clear that development granted retrospective planning permission under section 73A cannot obtain a CIL relief or exemption, apart from the separate minor development exemption.

This can be particularly painful where a householder originally had an exempt extension permission but the works depart so far from the approved scheme that a retrospective section 73A permission is later needed. The earlier exemption does not simply carry across to the retrospective permission.

If the built extension differs materially from the approved drawings, check the CIL consequences before choosing how to regularise the planning breach.

 

Can you appeal if the extension exemption is refused?

 

There is no specific statutory CIL appeal against a decision on the residential extension exemption. Government guidance expressly distinguishes this from the narrow regulation 116A appeal available for an annexe curtilage dispute.

If the problem is instead the authority’s calculation of the chargeable amount, the ordinary regulation 113 review and regulation 114 Valuation Office Agency appeal route may be available, subject to its short deadlines and the rule that commencement can close those routes. See our CIL appeals guide.

If the underlying planning application for the extension is refused, that is a separate planning decision and can usually be challenged through the normal planning appeal route.

 

Planning permission and the cost of applying

 

The CIL exemption is separate from the planning permission for the extension. Depending on the size, position and history of the house, an extension may need planning permission, prior approval or may fall within permitted development rights. Our home extension guide explains the planning side.

Any planning application or prior approval fee is separate from CIL and depends on the application being made. See our planning application fees guide.

 

Relevant CIL rules and guidance

 

• Regulation 42A: residential annexes and extensions
• Regulation 42B: claiming the exemption
• Regulation 67: Commencement Notice
• Government CIL guidance on residential extensions

Community Infrastructure Levy (CIL)

 

CIL Extension Exemption Page Created: 30th August 2026