Office to residential under prior approval, floor by floor
A three storey office of 980 square metres produced seven flats, not eleven. Daylight on the deep ground floor and noise from the workshop next door removed the other four.
Converting an office to flats under Class MA is a prior approval application, not a planning application, and the authority can only consider the matters the Order lists. In the illustrative scheme below, a three storey 1970s office building of about 980 m² produced seven flats rather than the eleven the first sketch showed, because natural light on the ground floor and noise from the workshop next door removed four of them. The building, the figures and the outcome are illustrative and assembled to show the sequence rather than to report a real decision.
Class MA sits in Part 3 of Schedule 2 to the General Permitted Development Order 2015 and allows a change of use from Class E to Class C3 dwellinghouses, subject to conditions and to prior approval of specified matters.
The building and the vacancy position
Assume a detached building on an edge-of-centre road: ground, first and second floors, a central stair and lift core, windows on the front and rear elevations only, and a yard to one side shared with a vehicle repair workshop. Floor plates are deep, roughly 15 metres front to back.
Class MA requires the building to have been in Class E use for a continuous period of at least two years before the date of the application. The illustrative building had been occupied as offices for eleven years, with a short serviced-office tenancy at the end, so the two year test was satisfied on the lease history and the rating record.
The vacancy position and the floorspace cap that applied when Class MA was introduced in 2021 have both been amended since, so read the current text of Class MA before relying on either. In the illustrative case the building had been empty for five months anyway, documented by a vacant rates certificate, meter readings and dated photographs of the interior.
Evidence of continuous Class E use is the item most often missing. Pull the leases, the rating list entries and the service contracts together before anything else.
The prior approval matters engaged
The Order restricts the authority to the matters it lists, which for Class MA include transport and site access, contamination, flooding, the impact of noise from commercial premises on the intended occupiers, the provision of adequate natural light in all habitable rooms, and, in a conservation area, the effect of changing a ground floor use on the character of the area. Industrial area impacts and the loss of certain services can also be engaged.
Two of those drove the design here: natural light and noise.
Contamination and flooding were screened rather than assessed in depth. The site was in Flood Zone 1 and had no industrial history on the historic maps, so a short screening note with the map extracts answered both, with the contaminated land position confirmed as low risk for a building reuse with no ground works.
Access was unchanged. Seven flats generate fewer vehicle movements than an office of that size, and a short note comparing parking demand with the existing provision closed the point.
Daylight to single aspect units
The ground floor was where the scheme lost units. With windows on two elevations only and a 15 metre depth, any ground floor flat behind the core was single aspect with a habitable room more than 7 metres from a window.
Three options were tested. Rooflights were impossible because two floors sat above. Light wells to the front required excavation and took away the parking. Cutting a slot through the floor plate to bring light down from the first floor lost more area than it gained.
The answer was to abandon residential use at the rear of the ground floor and keep a Class E unit there. That change meant the ground floor residential element occupied only the front bay, giving one flat with a properly lit living room and bedroom.
A Daylight and Sunlight Assessment was prepared for the ground and first floors, reporting average daylight factor and no-sky line results room by room. Councils usually expect a suitably qualified author for this work, and professional review is strongly advised. The assessment is what turned a subjective argument about adequacy into a room-by-room table.
Noise from the adjoining use
The repair workshop operated 8am to 6pm on weekdays with occasional Saturday working, using impact tools and a compressor in an open-sided bay 6 metres from the flank wall.
A Noise Impact Assessment measured the existing sound climate at facade positions over a working week, assessed it against internal criteria for living rooms and bedrooms, and set out the glazing and ventilation specification needed to meet them. The flank elevation had no windows, which helped considerably. The rear elevation faced the yard and needed acoustic glazing with mechanical ventilation so that occupiers would not have to open windows for fresh air.
The important point for the application was framing. Under Class MA the question is the impact of noise from commercial premises on the intended occupiers, so the assessment had to show the proposed flats would be acceptable, rather than arguing that the workshop should change its operation.
Space standards and the unit mix
Class MA conversions must meet the nationally described space standard, which fixes minimum gross internal areas by number of bedrooms and bedspaces, minimum bedroom sizes and a minimum built-in storage allowance. That standard, rather than the market, set the unit mix.
The resulting schedule across the three floors was one one-bedroom flat on the ground floor front, three on the first floor and three on the second floor, of which two were two-bedroom units where the floor plate allowed a dual aspect corner.
The eleven units in the first sketch failed on three counts: two were below the minimum area for a one-bedroom single-person flat, three had bedrooms under the minimum bedroom size, and two had no storage provision at all. Drawing the storage in at the start would have saved a fortnight.
The approach to carving flats out of an existing structure is the same one described in the flat conversion of a large Victorian house, with the difference that a prior approval route gives the authority no say on internal layout beyond the listed matters.
Documents submitted
The prior approval application comprised the following.
- The prior approval application form and the fee from the current fee schedule.
- A location plan and a block plan showing the yard and the workshop.
- Existing and proposed floor plans at 1:100 with every room dimensioned and areas scheduled against the space standard.
- Existing and proposed elevations, showing the glazing changes and the mechanical ventilation terminations.
- Evidence of the two year Class E use: lease schedule, rating list extracts and service contracts.
- Evidence of vacancy: vacant rates certificate, meter readings and dated interior photographs.
- The daylight assessment, room by room.
- The noise assessment with the glazing and ventilation specification.
- A flood and contamination screening note with map extracts.
- A short transport and parking note.
Biodiversity net gain did not apply, because the biodiversity gain condition attaches to planning permissions granted on an application rather than to development permitted by the Order. Community infrastructure levy liability is a separate question and depends on the authority's charging schedule and the offset for existing lawful floorspace, so check it before commencement.
Conditions and what they required before occupation
Prior approval was granted with conditions, and three of them governed the programme.
The development had to be completed within three years of the date of the prior approval, which is a condition of Class MA rather than a discretionary addition. The glazing and mechanical ventilation had to be installed in accordance with the approved noise report before first occupation, with a post-installation verification letter from the acoustician. And the retained Class E unit at the rear of the ground floor had to be kept available for that use, which the authority secured by reference to the approved plans.
Building Regulations ran in parallel and controlled matters the prior approval did not touch: means of escape from the common stair, fire resistance between flats, sound insulation between dwellings, and ventilation under Part F. A conversion that satisfies Class MA and fails Part B is still undeliverable, so run the fire strategy alongside the application rather than after it.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and read the current text of Class MA before assuming any limit or condition still applies.
For specialist technical reports, qualified professional input may be required. Browse the PlanScope report types to see which documents a prior approval conversion is likely to need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What does Class MA allow?
Class MA in Part 3 of Schedule 2 to the General Permitted Development Order 2015 permits a change of use from Class E, the commercial, business and service class, to Class C3 dwellinghouses, subject to conditions and to prior approval of listed matters. It is a prior approval route rather than a planning application, so the authority's consideration is confined to those matters.
How long must the building have been in Class E use?
A continuous period of at least two years before the date of the application. Evidence usually comes from the lease history, the rating list entries and service contracts. Other requirements that applied when Class MA was introduced in 2021 have been amended since, so read the current text of the Class rather than relying on a summary.
Does natural light matter in a prior approval conversion?
Yes. The provision of adequate natural light in all habitable rooms is one of the matters the authority considers, and it is the usual reason deep plan floorplates yield fewer units than a first sketch suggests. A room-by-room daylight assessment turns a subjective argument into a table the officer can check.
Do space standards apply to a Class MA conversion?
Yes. New dwellinghouses created under Class MA must meet the nationally described space standard, which sets minimum gross internal areas by bedrooms and bedspaces, minimum bedroom sizes and a built-in storage allowance. Drawing the storage in at the start avoids redesigning the whole floor plate later.
Does biodiversity net gain apply to prior approval?
No. The biodiversity gain condition attaches to planning permissions granted on an application, not to development permitted by the General Permitted Development Order. Community infrastructure levy liability is a separate matter that depends on the charging schedule and the offset for existing lawful floorspace, so check it before commencement.
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.