Fire safety in Class MA conversions to housing

Class MA of Part 3 of Schedule 2 to the GPDO 2015 allows a change of use from commercial, business and service use to dwellinghouses through prior approval rather than a full planning application. The list of matters the authority may consider is closed, and fire safety is not on it. So a council can be obliged to grant prior approval for a conversion that could never satisfy Part B of the building regulations, and applicants sometimes take that grant as evidence the scheme works.

It is not. The prior approval and the building control approval answer different questions, and the second one is where office to residential conversions fail.

What the prior approval covers

The matters an authority may consider under Class MA are transport impacts, contamination risk, flooding risk, impacts of noise from commercial premises on intended occupiers, the impact of introducing residential use into an area the authority considers important for general industry, storage, distribution, waste or retail, the impact on the character or sustainability of a conservation area where the building is in ground floor commercial use, and the provision of adequate natural light in all habitable rooms.

The class has been amended since it was introduced, including changes to the floorspace limit and the vacancy requirement, so read the current text before advising on eligibility. Design, amenity space, internal layout, unit mix and fire safety are outside the authority's reach.

Natural light is the matter that refuses schemes. A 1970s office floorplate 25 metres deep with a central core produces habitable rooms with no window at all unless the plan is reworked, and reworking the plan changes the escape strategy. The two questions are linked even though only one of them is a planning matter.

Escape from converted upper floors

Start here, because it determines how many units fit on a floor and where they sit.

Offices are typically designed with escape in two directions to two stairs, or with a single stair and travel distances based on office occupancy. Residential escape strategies are different. Flats are designed on the basis that a fire is contained within the flat of origin, with a protected common corridor and a protected stair, and with travel distance limits from the flat entrance door to the stair.

That has consequences on a deep plan. Dead-end corridors have tight travel distance limits. Flats opening directly onto a stair enclosure are restricted. A single stair building has its own constraints, and policy and guidance on single stair residential buildings has been under active review, so check the current position rather than a scheme precedent from a few years ago.

The practical result is that the number of units per floor is usually set by the corridor and stair arrangement, not by the daylight or the sales mix.

Existing compartmentation and its limits

An office building's compartmentation was designed for offices. Conversion to flats requires compartment walls and floors between dwellings, fire resisting construction to the common escape route, and protection of every penetration through those elements.

The items that consume budget on real projects are service risers that were never fire stopped to a residential standard, raised access floors and suspended ceilings that allow smoke to pass over partitions, curtain walling where the perimeter junction with the floor slab has no cavity barrier, and existing glazed internal screens with no fire rating.

Investigate before you buy. Opening up two or three representative locations tells you more about the conversion cost than any desktop review, and the findings frequently change the offer.

External wall construction is the other item to establish early. Where a building has a rainscreen or curtain wall system, the materials in the external wall and the cavity barrier arrangement matter for residential use in a way they did not for offices, and the record drawings are often silent on the build-up. Establishing what is actually there can take an intrusive survey and a materials review, and the answer sometimes ends the project.

Where the regulator becomes involved

The building safety regime introduced by the Building Safety Act 2022 applies staged control to higher-risk buildings, defined by height or number of storeys together with the presence of at least two residential units. A commercial building converted to flats can cross into that category simply by changing use.

Where it does, building control approval must be obtained from the regulator before construction starts, and a completion certificate is needed before occupation. Both stages have statutory periods and both involve a level of documentation well beyond a conventional building control submission. Programmes that assume a local authority building control timetable will slip.

The planning stage fire statement requirement in article 9A of the procedure order is framed around applications for planning permission. A Class MA application is a prior approval application, so the requirement does not attach in the same way, and applicants should confirm the position with the authority rather than assume it either way. Where a scheme involves any element needing planning permission alongside the prior approval, for example external alterations, the requirement may be engaged by that application.

Building regulations obligations at conversion

A material change of use triggers requirements under the building regulations even where no building work would otherwise be done, and fire safety requirements are among them. In practice a conversion engages requirements on means of warning and escape, internal and external fire spread, and access and facilities for the fire service.

Fire service access and water supplies are an early check, because a building that was acceptable as an office may not have the hydrant provision or vehicle access expected for residential occupation. Getting that wrong late is expensive, and it sits alongside fire service access and water supplies at planning stage as an item to resolve before layouts are fixed.

What to submit with the prior approval

You do not have to submit a fire strategy, and the authority cannot refuse for the want of one. Submit enough anyway.

An outline fire strategy showing the stair and corridor arrangement, travel distances and compartmentation intent does two things. It demonstrates that the unit layout you are relying on for the natural light case is the layout that can actually be built. And it gives the case officer confidence that the scheme is real, which matters on borderline judgements about light.

Pair it with daylight modelling for every habitable room rather than a statement that each room has a window. That is the evidence the natural light matter turns on, and it should use a recognised method with the assumptions stated, including reflectances and any obstruction from neighbouring buildings.

Add a noise assessment where commercial premises remain in the building or next door, since that is another prior approval matter and the two often arrive together on a mixed parade. And keep the drawings consistent between the two submissions. A prior approval layout that differs from the building control layout is a common source of argument about whether the approval was implemented at all.

PlanScope drafts the supporting documents around the application, including the Fire Statement and the Structural Survey, for review by a qualified author. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. A Fire Statement and a fire safety strategy require someone with the necessary fire engineering competence, and PlanScope's draft is a starting point for that professional rather than a substitute. This is general guidance, not legal advice, so check the position with your local planning authority before relying on it.