The levy exemption for residential extensions

The CIL extension exemption means almost no householder pays the community infrastructure levy on an extension, and the handful who do pay it because of paperwork rather than because of floorspace. There are two routes to relief: the minor development rule, which exempts new build floorspace of less than 100 square metres where no new dwelling is created, and the separate residential extension exemption, which removes the size limit altogether for an extension to an existing dwelling.

Both have to be claimed, and the claim has to be made and accepted before a spade goes in the ground. Miss that sequence and the exemption is gone, whatever the merits.

The threshold that makes most extensions exempt

Regulation 42 of the Community Infrastructure Levy Regulations 2010 exempts minor development: where the gross internal area of new build floorspace is less than 100 square metres, no levy is chargeable, provided the development does not comprise one or more dwellings.

That covers the great majority of domestic work. A single storey rear extension, a side infill, a loft conversion with a dormer and a garage conversion all sit well below the threshold. The exemption under this rule operates automatically, without a claim, which is why most householders never hear about the levy at all.

The proviso is the part worth reading twice. Create a dwelling, however small, and the minor development rule stops applying regardless of floorspace. A 45 square metre annexe that is a separate dwelling is outside regulation 42 entirely, and needs a different exemption.

Where an extension becomes chargeable anyway

Three situations push an extension into chargeable territory.

The first is size. Where new build floorspace reaches 100 square metres or more, the minor development rule no longer helps and the residential extension exemption has to be claimed instead. Large two storey rear and side extensions on substantial houses reach that figure more often than people expect, particularly where a garage and a garden room are included in the same permission.

The second is the creation of a dwelling. A self-contained annexe, a flat over a garage or a subdivision creates a dwelling, and the levy applies subject to the annexe or self-build exemptions.

The third, and the most common in practice, is procedural failure. The development was exempt in principle, the exemption was not claimed, or it was claimed but the commencement notice was never submitted, and the authority issued a demand notice for the full amount plus a surcharge. Charging authorities have limited discretion once the sequence has been broken.

Annexes, and the separate exemption

A residential annexe sits in its own exemption, with conditions the extension exemption does not carry.

The exemption applies to an annexe within the curtilage of the claimant's own dwelling, where the claimant owns a material interest in that dwelling and occupies it as their sole or main residence. So a landlord cannot claim it on a rented property, and a developer cannot claim it on a house they do not live in.

The annexe also has to remain an annexe. Where, within three years of completion, the annexe is let separately, sold separately, or the main dwelling is sold without the annexe, the exemption is withdrawn and the levy becomes payable. That three year clawback is the detail most often overlooked, and it has practical consequences for anyone building an annexe with a view to a sale or a rental income.

Where the annexe is intended as a separate dwelling from the outset and the owner will occupy it themselves as their principal residence, the self-build exemption may be the better route, and it has its own three year clawback and its own evidence requirements.

Claiming before works start

The procedural sequence is the whole of the risk, and it is short enough to memorise.

1. Planning permission is granted and the charging authority issues a liability notice setting out the chargeable amount.
2. Someone assumes liability for the levy, using the authority's form. Until liability is assumed, no exemption can be granted.
3. The exemption claim is submitted, on the correct form for the relief sought.
4. The authority notifies its decision on the claim.
5. A commencement notice is submitted, specifying the date development will start, and that date must be after the authority has granted the exemption.
6. Development starts on or after the notified date.

Each step has to happen in that order. An exemption claimed after work has begun cannot be granted. A commencement notice submitted late, or not at all, removes an exemption that had already been granted.

Dates are the thing to watch. On a small project the builder often starts within days of being instructed, and demolition, site clearance or digging foundations can all constitute the commencement of development. Tell the builder, in writing, not to start before you confirm.

The commencement notice people forget

This is worth its own section because it accounts for most levy bills on domestic extensions.

The commencement notice is a short form stating when development will begin. It is separate from the exemption claim, separate from any building control notification, and separate from anything the planning department asks for. Submitting it is the claimant's responsibility, and the authority has no obligation to remind anyone.

Where it is not submitted before development begins, the exemption lapses and a surcharge can be imposed on top of the levy. Appeals against surcharges are available on limited grounds, and the ground that the claimant did not know about the requirement is not one of them.

Send it by a method that produces a receipt, and keep the receipt with the permission. On a project managed by an architect or agent, agree explicitly who is sending it, because this is exactly the kind of task that falls between two parties. Our note on what a planning agent's fixed fee includes covers the broader question of which administrative steps sit inside a professional appointment and which do not.

Measuring gross internal area correctly

Floorspace for levy purposes is gross internal area, measured to the internal face of the external walls, including internal walls, stairwells and circulation.

Two deductions matter. Floorspace in buildings that are to be demolished is deducted, and so is floorspace in an existing building that has been in lawful use for a continuous period of at least six months within the three years before the permission first permits development. That second deduction is why converting an existing garage, which has been in use, is treated differently from building a new one.

The in-use test catches people on properties that have stood empty. A house unoccupied for several years before purchase may not satisfy the six month requirement, and that changes the arithmetic on a conversion scheme. Gather the evidence of occupation early, because reconstructing it later from utility records is difficult.

Where the figures are close to the 100 square metre line, have them measured properly from the approved drawings rather than estimated. Charging authorities calculate from the drawings, and a discrepancy is resolved in the authority's favour unless you can show the measurement is wrong.

Evidence to keep on file

Keep one folder, for at least four years after completion and longer where an annexe is involved.

The liability notice. The assumption of liability form and its acknowledgement. The exemption claim and the authority's decision granting it. The commencement notice and proof of its submission date. The approved drawings used for the floorspace calculation, with the calculation itself. Evidence of lawful use for any existing floorspace deducted, such as council tax records or utility bills covering the relevant six months. For an annexe, evidence of your occupation of the main dwelling as your sole or main residence.

That last item matters if the property is sold within the clawback period, because a buyer's solicitor will raise the levy position and an unresolved charge sits on the land. The levy is a charge that can be registered against the property, so an unpaid demand is not a problem that stays with the person who caused it.

Where an extension turns out to need a certificate to confirm what was lawfully there before, the costs of that exercise are set out in our guide to budgeting a lawful development certificate application.

Do two things today if you have permission for an extension. Check whether your authority has adopted a levy charging schedule at all, since many have not and the question then falls away. And if it has, work backwards from the date your builder wants to start and diary the steps above, leaving a clear fortnight for the authority to determine the exemption claim.

If you also need the supporting documents for the application itself, the pricing page sets out what a draft report costs, and the report index shows which documents a householder scheme usually needs.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.