Part 7 Class H: extending an industrial building or warehouse
Class H permits industrial and warehouse extensions without an application, inside cumulative floorspace, height and boundary limits. The parking condition and the meaning of the original building defeat more schemes than the headline figures.
Class H of Part 7 of Schedule 2 to the General Permitted Development Order 2015 allows the erection, extension or alteration of an industrial building or a warehouse without a planning application, inside limits on floorspace, height and position. For most sites outside a designated area that means a cumulative addition of up to 1,000 m² and up to 50 per cent of the gross floor space of the original building, whichever bites first. The figures fall to 200 m² and 25 per cent on article 2(3) land. No prior approval is required, which makes Class H unusually clean compared with the residential classes, and unusually easy to overrun without noticing.
What the class actually covers
Class H is defined by what happens in the building rather than by the use class on the title deeds. Part 7 defines an industrial building by reference to the carrying out of an industrial process, and a warehouse by reference to storage or distribution. That distinction matters more than it used to. When light industrial moved into Class E in September 2020, plenty of buildings acquired a use class label that tells you nothing about whether Class H is available. Read the definitions at the end of Part 7 against what the occupier does, and check the planning history for any condition restricting the use.
The right belongs to the industrial or warehouse undertaking on the premises. An office block, a retail unit or a building in mixed occupation does not get there, and neither does a building whose industrial use has lapsed. Where the site has been vacant for a long period, establish the lawful use first, because the whole right depends on it.
The floorspace and height limits
Four numerical limits do the work, and they apply cumulatively across everything built under the class since the relevant date.
| Limit | Outside article 2(3) land | On article 2(3) land |
|---|---|---|
| Cumulative gross floor space of development under the class | 1,000 m² | 200 m² |
| Increase over gross floor space of the original building | 50 per cent | 25 per cent |
| Height where any part is within 10 m of a curtilage boundary | 5 m | 5 m |
| Height elsewhere | No higher than the building being extended | No higher than the building being extended |
Read the two floorspace limits together. On a 1,200 m² original unit the percentage limit gives 600 m², so the 1,000 m² ceiling never comes into play. On a 40,000 m² distribution shed the percentage is irrelevant and the 1,000 m² cap is the binding constraint. The word that catches people out is original, meaning the building as it stood on 1 July 1948 or as first built if later, so a unit already extended twice may have very little left.
Height is measured on the building as extended or altered. A new element within 10 metres of any boundary of the curtilage cannot exceed 5 metres, which rules out most modern eaves heights on tight urban estates. Beyond that distance the extension simply cannot rise above the building it is attached to.
Position, parking and the conditions that come attached
Two positional rules sit alongside the height test. A building erected under the class must not stand within 5 metres of any boundary of the curtilage of the premises. And the development must not reduce the space available for the parking or turning of vehicles on the site.
That parking condition is the one that quietly defeats schemes. Yard space on an industrial estate is usually working space for articulated vehicles, and an extension that swallows a turning head takes the proposal outside the class even if every floorspace figure is comfortable. Survey the yard, plot the swept paths before and after, and keep the evidence.
The class also carries use and appearance conditions. Development permitted by Class H must be used only for the purposes of the industrial process or the storage or distribution use carried on at the premises, or for a purpose incidental to it. Materials must be similar in appearance to those of the existing building. A cladding change from profiled steel to a different colour and profile is a legitimate question to ask yourself before starting, and it is a poor thing to argue about after the frame is up.
Article 2(3) land, listed buildings and hazard areas
Article 2(3) land means a conservation area, a National Park, the Broads, an area designated as a National Landscape (formerly an area of outstanding natural beauty) or a World Heritage Site. On any of those, the reduced 200 m² and 25 per cent figures apply.
Class H is not available at all within the curtilage of a listed building. It is also excluded on land that is or forms part of a safety hazard area or a military explosives storage area, which is a live issue near fuel depots, chemical works and certain defence sites. Both are worth checking on the council's constraints layer before design work starts, because neither is obvious from the site.
Article 4 directions can withdraw the right as well. They are less common on industrial land than in residential conservation areas, though some authorities have used them around sensitive boundaries. A quick check of the council's Article 4 register is far better insurance than an enforcement notice.
How earlier extensions consume the allowance
The cumulative wording is unforgiving. Every square metre erected, extended or altered under Class H counts against the 1,000 m² and against the percentage, whether it was your company that built it or a predecessor.
That means the planning history is the first document to obtain, not the last. Ask for the file, look for previous certificates of lawfulness, and compare the current footprint against historic mapping. Where an earlier extension was built under a full permission rather than under the class, it does not consume the Class H allowance, though it does increase the building and therefore changes nothing about the original building figure, which stays fixed.
Where the allowance has run out, the fallback is an ordinary planning application. A short Planning Statement setting the extension against the local plan's employment land policies usually carries a well-sited industrial extension, and the evidence base is far lighter than for a new unit.
Environmental permits and EIA screening cut across the right
Permitted development rights do not suspend other regimes. A site holding an environmental permit will normally have permit conditions on emissions, storage, drainage and site layout, and extending the building can require a permit variation regardless of the planning position. Deal with the regulator in parallel rather than afterwards.
There is also a planning gate. Article 3 of the General Permitted Development Order withholds permission for development that is EIA development, unless the local planning authority has adopted a screening opinion that it is not, or the Secretary of State has directed accordingly. Schedule 2 to the Environmental Impact Assessment Regulations 2017 catches industrial estate development and certain installations at stated thresholds, so a large extension on a sensitive site is not automatically outside the regime. Where there is any doubt, request a screening opinion. It is a short process and it produces the piece of paper a funder will ask for. An Environmental Impact Assessment is a document that the 2017 Regulations require to be prepared by competent experts, so treat any AI-assisted draft as material for that expert rather than as the assessment itself.
Confirming the position before you build
A lawful development certificate under section 192 of the Town and Country Planning Act 1990 is the only formal way to establish that proposed works are lawful. The council determines whether the description of the works falls within the class on the facts and the law, and the certificate binds it.
- Establish the lawful use of the building and its planning history.
- Measure the original building and calculate both floorspace limits.
- Plot boundary distances, height points and the yard layout before and after.
- Check article 2(3) status, listed building curtilage, hazard areas and any Article 4 direction.
- Apply for a certificate under section 192 with drawings, measurements and the calculation shown.
Certificates carry a fee and an eight week determination period, and the fee is a fraction of what a refused enforcement appeal costs. Funders and purchasers ask for them. So do insurers, when a building turns out to have no consent behind it.
Enter your postcode on PlanScope to see which reports an industrial extension on your site is likely to need, or browse the report types by category first. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance rather than legal advice, and permitted development rights are amended frequently, so check the current consolidated text of the Order and confirm the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
Does Class H need prior approval?
No. Unlike the residential and change of use classes, Class H of Part 7 grants permission outright where the limits and conditions are met, with no prior approval application. That makes a lawful development certificate under section 192 the sensible way to record the position, because nothing else creates a document confirming the works are lawful.
What counts as the original building for the percentage limit?
The building as it stood on 1 July 1948, or as first built if it was constructed after that date. Later extensions do not raise the baseline. A unit that has already been extended twice may therefore have almost no percentage allowance left, even though the building on the ground today looks large enough to justify more.
Can I use Class H if my unit is now in Class E?
Possibly. Part 7 defines an industrial building by reference to the industrial process carried out rather than by use class, so the September 2020 move of light industrial into Class E does not by itself remove the right. Check the definitions at the end of Part 7 against what the occupier actually does on the premises.
How close to the site boundary can the extension go?
A building erected under Class H must not be within 5 metres of any boundary of the curtilage of the premises. Separately, where any part of the development sits within 10 metres of a boundary, the height of the building as extended cannot exceed 5 metres. Both limits are measured to the curtilage boundary, not the red line.
Do permitted development rights override an environmental permit?
No. Permit conditions on emissions, drainage, storage and layout continue to apply, and extending a permitted installation may need a permit variation. Article 3 of the Order also withholds permission where the works amount to environmental impact assessment development, unless the council has issued a negative screening opinion.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.