Reports for converting offices above a shop to flats

Two first-floor offices above a parade shop, converting to two flats, with the shop staying put. The document set for that job is short, and it is driven by two questions a council will test hard: can every habitable room get adequate natural light, and will the people living above the shop be bothered by the shop. Get those two answered properly and the rest is paperwork.

Which route you take decides how much paperwork. Prior approval under Class MA of the General Permitted Development Order 2015 limits what the authority may consider. A full application opens everything up.

Which route applies: prior approval or full application

Class MA in Part 3 of Schedule 2 to the Order permits a change from Class E commercial, business and service use to Class C3 dwellinghouses, subject to prior approval. The gateway conditions are strict. The building must have been in a qualifying Class E use for at least two years before the application, it must have been vacant for at least three continuous months immediately before it, and the floorspace changing use must not exceed 1,500 m². Listed buildings and scheduled monuments are excluded.

Upper-floor offices above a trading shop trip up on vacancy more often than on anything else. If a tenant moved out six weeks ago, the application is premature, and the sensible move is to diarise the date rather than submit and be refused.

Where Class MA is not available, a full planning application follows, and the council then assesses design, external alterations, amenity, parking, refuse, overlooking and the loss of the office use against the adopted local plan. That is a larger evidence base and a longer determination period: eight weeks for a minor application against the shorter prior approval period.

Natural light to all habitable rooms

Adequate natural light in all habitable rooms is one of the matters the authority must consider on a Class MA prior approval, and it is the condition that kills the most upper-floor schemes. A rear bedroom lit only by a borrowed light from a corridor, or a windowless box behind a retained stair core, will not pass.

What satisfies a case officer is a daylight note keyed to the proposed layout: window sizes and head heights, room depths, orientation, any obstruction from the building opposite, and a statement of which rooms are habitable. Where a room is tight, an average daylight factor calculation or a no-sky line check gives the officer something to hold on to. A Daylight and Sunlight Assessment is the fuller version of the same evidence and is worth commissioning where a layout depends on one marginal room.

Bathrooms, hallways and utility rooms are not habitable rooms. Kitchens usually are, and an internal kitchen within an open-plan living space is the standard way round a deep plan.

Noise from the commercial use below

The second prior approval matter that bites is the impact of noise from commercial premises on the intended occupiers. A bakery with a 4am start, a takeaway with an extract fan on the rear elevation, a pub with a cellar hatch, a convenience store with a chiller compressor: each needs assessing rather than asserting.

The evidence is a Noise Impact Assessment measuring the existing plant and activity at the proposed window and floor positions, comparing the result against the internal guideline levels in BS 8233:2014, and specifying what gets installed. For a flat above a retail unit that usually means some combination of:

• an acoustic floating floor or resilient ceiling treatment between the commercial unit and the flat
• glazing and acoustically attenuated background ventilation to the affected elevations
• relocating or re-timing plant serving the commercial unit, agreed with the occupier
• siting bedrooms away from the plant elevation

Structure-borne sound is the part that gets missed. Airborne measurements at a facade say nothing about a compressor bolted to a shared floor slab, so the survey needs to cover both paths.

Refuse, cycle storage and access

The two routes diverge sharply here. On a Class MA prior approval, the authority's consideration is limited to the matters the Order lists, and refuse storage, cycle parking and external appearance are not among them. That does not mean you can ignore them.

Building Regulations and the waste collection service still apply, and a scheme with nowhere to put four bins will be unlettable and may attract a condition at the fire safety or licensing stage instead. Show bin and cycle storage on the proposed plans even where the officer cannot refuse you for it. On a full application it is a refusal reason in its own right, and the local plan or a parking standards document will set the numbers.

Safe site access is a listed prior approval matter, so where the only route to the flats is through a yard shared with the shop's deliveries, a short access note with a layout drawing earns its place.

Space standards and internal layout

Dwellings created under permitted development rights in England must meet the Nationally Described Space Standard. The figures that matter for small upper-floor conversions are a minimum gross internal area of 37 m² for a one-bedroom one-person flat with a shower room, 39 m² where it has a bathroom, and 50 m² for a one-bedroom two-person flat, with a floor-to-ceiling height of at least 2.3 m over 75 per cent of the area.

That last figure quietly rules out a lot of attic space above shop parades. Measure before you draw.

Built-in storage counts towards the area, and the standard sets minimum storage of 1 m² for a one-person dwelling and 1.5 m² for two. State the GIA of each unit on the plans. An officer who has to measure your drawing to check compliance will take longer and may simply ask.

Fire separation and escape

Planning and Building Regulations part company here, but the design has to work for both. A flat above a commercial unit needs fire separation between the uses and a protected means of escape that does not pass through the shop, which often forces a separate street door and a protected stair.

For most two-flat conversions above a parade this is a Building Regulations matter under Approved Document B rather than a planning one. A Fire Statement under Article 9A of the Development Management Procedure Order is only triggered for relevant buildings at 18 m or more in height or seven or more storeys, which a two-storey parade will not reach. Where it is triggered, it must be prepared by someone with the necessary fire engineering competence, and that is a legal requirement rather than a preference.

Contamination and flooding matters

Both appear on the Class MA list. On a town centre parade, contamination is normally dealt with by a short desk study confirming the historical land use and the absence of a pathway to new residential receptors, since no ground is being disturbed.

Flooding is the one to check first on the Environment Agency maps. In Flood Zone 2 or 3 the prior approval will need a Flood Risk Assessment addressing residual risk, safe access and egress, and flood resilience. Upper-floor flats are often the easy case, because the habitable accommodation sits above any modelled level, but the assessment still has to say so and deal with access during an event.

What prior approval cannot consider

The limits are the point of the route. On a Class MA application the authority cannot refuse on design, on the external appearance of new windows, on the loss of the office use as employment floorspace, on parking provision, or on general amenity grounds outside the listed matters. In a conservation area it may consider the impact of losing a ground floor use, which for an upper-floor conversion with the shop retained does not arise.

But external alterations usually do need separate consent. New rooflights, a new street door, a rear dormer or an extract duct are works rather than a change of use, and Class MA covers only the change of use. Many apparently simple conversions therefore need two submissions, and submitting them together keeps the case officer from treating the second as an afterthought. If the alternative plan is a shared house rather than self-contained flats, the evidence base shifts again, and our note on reports for a large HMO of seven or more people covers that pack.

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