Walkthrough: office to flats under Class MA

A class ma conversion walkthrough is most useful when it follows the evidence rather than the architecture, because prior approval under Class MA is decided on a short list of prescribed matters and everything else is outside the council's reach. What follows is an illustrative example, written to show the order in which the evidence lands and what the final document pack contained. It is not a real case and no figure in it describes a real building.

The subject is a three-storey 1970s office building on a town centre secondary street, roughly 620 square metres over three floors, vacant for eight months after a single tenant left, with a public house sharing a party wall. Nine flats were proposed.

The building, its vacancy and the qualifying tests

Class MA sits in Part 3 of Schedule 2 to the General Permitted Development Order 2015 and permits change of use from Class E, the commercial, business and service class, to Class C3 dwellinghouses. The qualifying conditions are factual and they are the first thing to check.

The building must have been in a Class E use for a continuous period before the application, and a vacancy requirement has applied. Class MA has been amended more than once, and the floorspace limit that originally capped conversions at 1,500 square metres was removed in 2024. Read the current text of Class MA on legislation.gov.uk before relying on any qualifying condition, because the continuous use period, the vacancy period and the exclusions have all been the subject of amendment.

The exclusions also have to be cleared. Class MA is unavailable on listed buildings and land within their curtilage, on scheduled monuments and in a number of other designated situations, so check the list in the current text against the site rather than assuming.

Two pieces of evidence covered the qualifying tests in the illustrative case: a schedule of the previous tenancy with the lease dates, and marketing particulars with dated portal screenshots showing the building empty. Officers accept that combination readily. They do not accept an assertion in a covering letter.

Natural light evidence for habitable rooms

Adequate natural light in all habitable rooms is a prescribed prior approval matter, and it is the one that fails conversions of deep-plan office buildings. The council can refuse where habitable rooms would not have adequate natural light, and a room with no window at all is a refusal regardless of any other merit.

The illustrative submission did three things. It provided floor plans with every window dimensioned and every habitable room labelled and measured. It set out a daylight calculation for the rooms with the least favourable aspect, using the method in the current national guidance on daylight in these conversions. And it redesigned two units, converting what would have been internal bedrooms into a single larger open plan space with a window, rather than arguing that a borrowed light arrangement was adequate.

That redesign is the practical lesson. A deep plan floor produces fewer, larger flats if the natural light test is respected, and a scheme that ignores it produces a refusal and a wasted fee. Where the daylight position is finely balanced, a Daylight and Sunlight Assessment prepared to the current BRE guidance carries more weight than plan dimensions alone, and councils expect a suitably qualified author for that work.

Noise from a neighbouring use

Impacts of noise from commercial premises on the intended occupiers is a prescribed matter, and the public house on the party wall made it the central issue in the illustrative case.

The assessment covered three sources: amplified music and patron noise through the party wall, patrons outside at closing time, and the pub's extraction and cellar plant on the rear elevation. Measurements were taken over a Friday and Saturday night and a weekday, with the internal noise criteria in BS 8233 as the target and the approach in the planning and noise guidance used to frame the assessment.

The mitigation that followed was a secondary independent wall lining to the party wall, acoustic glazing with mechanical background ventilation to the rear elevation rooms, and habitable rooms arranged away from the pub boundary at second floor level. The submission also set out an agent of change position: the pub was there first, so the burden of mitigation sat with the conversion. Councils respond well when that point is made explicitly rather than left to be inferred.

A Noise Impact Assessment of this kind is work councils usually expect a suitably qualified author to prepare, and professional review is strongly advised.

Flooding and contamination submissions

Flooding risk and contamination risk are both prescribed matters, and both were straightforward here.

The flood map for planning showed the site in Flood Zone 1 and the printed result with the site outlined was sufficient. Had the building sat in Zone 2 or 3, a flood risk assessment with finished floor levels, safe access and egress and a residual risk section would have been needed, and the sequential approach would have been argued.

Contamination on a town centre office site is usually a desk study exercise. The illustrative pack included a Phase 1 desk study covering the historical map sequence, which showed a former garage two doors away, and a conceptual site model concluding that the risk to future residential occupiers was low given the existing slab and the absence of ground works. A Contaminated Land Assessment at Phase 1 or Phase 2 has to be prepared in accordance with BS 10175 by a suitably qualified and experienced person, and an AI-assisted draft is a starting point for that professional rather than a substitute.

Space standards and unit layouts

New dwellings created through permitted development must meet the nationally described space standard. That requirement applies to Class MA conversions and it is not a prior approval matter to be argued about, it is a condition of the class.

The schedule submitted listed each of the nine flats with its gross internal area, bedroom count, bed spaces, individual bedroom areas, floor to ceiling height and built-in storage, set against the standard. Two units were combined to reach compliance, which is why the scheme ended at nine flats rather than eleven.

Storage is the line most often failed. The standard sets a built-in storage figure by dwelling type, and an open plan conversion with no cupboards will not meet it however generous the overall area.

What the council could and could not assess

The council assessed the prescribed matters and nothing else. It could not refuse on the external appearance of the building, on the absence of amenity space, on parking provision, on the loss of employment floorspace as a policy matter, or on the mix of unit sizes.

Three consequences followed. The application description had to be precise, because a description that strayed beyond the class would have invited a refusal on jurisdiction. No design and access statement was needed. And the biodiversity gain condition did not apply, because development under the General Permitted Development Order sits outside the mandatory biodiversity net gain regime.

One obligation that did apply was the Community Infrastructure Levy. Development under a general consent requires a notice of chargeable development to be submitted before work starts where the levy is engaged, and existing floorspace in lawful use can normally be offset. Missing that notice creates a surcharge, and it is the single most common administrative failure on permitted development conversions.

The final document list

• Prior approval application form under Class MA with the correct fee.
• Location plan at 1:1250 with the site edged red.
• Existing and proposed floor plans at 1:100 with every window dimensioned and habitable rooms labelled.
• Daylight calculation for the least favourable rooms, with assumptions stated.
• Noise survey and assessment against BS 8233 internal criteria, with a mitigation schedule.
• Flood map for planning result with the site outlined.
• Phase 1 contamination desk study with a conceptual site model.
• Space standard compliance schedule for all nine units.
• Evidence of previous Class E use and of the vacancy period.
• Notice of chargeable development for the Community Infrastructure Levy.

The determination period for a Part 3 prior approval is 56 days from a valid application. Diary it, because a decision issued outside the period has consequences set out in the Order.

Another route through the same class, this time from a retail unit, is set out in the shop to residential conversion walkthrough. Browse all 66 report types on PlanScope and start a draft for your conversion.

This article is general guidance, not legal advice, and the example in it is illustrative. Class MA has been amended more than once, so check the current text and 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.