Which reports an office to flats conversion needs

A full planning application to turn offices into flats carries a longer evidence list than the prior approval route, and most of the reports needed for an office to residential conversion follow from that one choice. Expect a planning statement, an internal daylight assessment, a noise assessment that deals with the commercial uses around the building, and a contamination desk study. Taller buildings add fire safety information. Class MA prior approval tests a short closed list of matters. A full application opens the whole development plan, including internal space, outlook and amenity policies that Class MA never reaches.

The route you pick sets the document list

Class MA of Part 3 of the General Permitted Development Order 2015 allows a commercial, business and service building in Class E to become dwellings in Class C3 with prior approval. It has conditions and exclusions, and a 2024 amendment changed two of the best known ones, so read the current consolidated text before you rely on any summary of it. Listed buildings and land within a site of special scientific interest sit outside the class altogether.

Full planning permission becomes the route when the building falls outside Class MA, when the scheme adds floorspace such as a roof extension, or when you want a layout that the prior approval conditions would block.

The second column is short by design. That is the attraction of prior approval and also its trap, because a scheme that squeezes through it can still be a poor building to live in.

Internal daylight decides more schemes than anything else

Office floorplates are deep. Residential rooms need light at the back of the plan, and a deep plan with a single window wall is where office conversions fail. The assessment work is an internal daylight study rather than the neighbour-facing loss of light exercise, so commission it early and let it shape the unit layout instead of validating one you have already drawn.

BS EN 17037 is the reference point for daylight provision in a room, and BRE 209 (2022) remains the guidance councils cite for site layout and for effects on neighbours. A daylight and sunlight assessment written after the layout is fixed tends to report a problem you can no longer solve.

Watch for rooms lit only by a recessed balcony, single aspect north facing flats and light wells that look generous on plan and perform badly in a model. Outlook is a separate point from daylight, and an officer will raise it where a window faces a wall two metres away.

Noise from the neighbours, and plant on the roof

Introducing homes into a commercial building means the existing uses around you become a constraint on your scheme. A restaurant extract fan, a gym, a service yard with early deliveries or a late licensed premises all produce noise at the facades you are about to put bedrooms behind.

A noise impact assessment for a conversion usually combines a baseline survey with internal target levels. BS 8233:2014 gives guideline internal ambient levels of 35 dB LAeq,16hr for living rooms in the day and 30 dB LAeq,8hr for bedrooms at night. Where the noise is from a specific commercial source rather than general road traffic, BS 4142:2014+A1:2019 is the right method and the answer is expressed as a rating level compared to background.

Two consequences follow that developers often miss. Acoustic glazing with mechanical ventilation can meet internal levels while leaving the scheme reliant on windows staying shut, which pushes you straight into overheating. And an officer can refuse on the agent of change principle if your mitigation would in practice force the existing business to change how it operates.

Ground conditions, contamination and flood risk

A Phase 1 desk study costs little relative to what it can find. For a building conversion the ground risk is usually limited to the site history and any basement, though a former industrial or garage use next door still matters. Where the desk study identifies a plausible pollutant linkage, Phase 2 intrusive work follows. Both stages sit within the contaminated land assessment family and must be prepared by a suitably qualified and experienced person working to BS 10175. This is one of the report types where professional authorship is not optional.

Flood risk is the other desk check. A conversion in Flood Zone 2 or 3 needs a flood risk assessment, and for a change of use the argument usually turns on safe access and egress, finished floor levels and a flood warning and evacuation plan rather than on displaced storage volume.

Fire safety once the building gets tall

For a relevant building, Article 9A of the Development Management Procedure Order 2015 requires a fire statement to accompany the planning application, and the Health and Safety Executive is a statutory consultee at that stage. Relevant buildings are broadly those of 18 metres or more in height, or seven or more storeys, containing two or more dwellings. This is Planning Gateway One.

A fire statement must be prepared by someone with the fire engineering competence to sign it. An AI-assisted draft can structure the document and identify the questions a competent author has to answer, and it is a starting point for that person rather than a replacement.

Space standards, amenity, bins and cycles

New homes created under permitted development rights must meet the nationally described space standard floor areas, which is a condition in the Order rather than a policy judgement. A one bedroom, one person flat at 39 m² and a one bedroom, two person flat at 50 m² are the figures most often quoted back at applicants.

Under a full application the position is different. The space standard applies where the local authority has adopted it as policy, and many have, sometimes with their own additions on room widths, storage and private amenity space. Check the adopted plan and any housing design supplementary document.

Then the practical list. Bin storage within a reasonable carry distance of the collection point, secure long stay cycle parking at the policy ratio, a refuse strategy the waste team will accept, and amenity space or a balcony where policy requires it. These are the details that trigger a request for further information after validation and cost you weeks.

An illustrative example: a 1970s three storey office over a parade of shops, converted to nine flats. The daylight model forced two units to be merged, the acoustic survey of the takeaway extract behind the building set the glazing specification, and the bin store had to move to the front because the rear yard was the only vehicle turning area. None of those three changes came from the planning statement.

Assembling the pack

1. Run the desk checks first: flood zone, contamination history, conservation area, listed building status and whether Class MA is available at all.
2. Commission the daylight study against a sketch layout, before the drawings are worked up.
3. Order the noise survey once you know which neighbouring uses matter, and at a time that captures their worst case.
4. Fix the unit mix and floor areas against the standard the authority actually applies.
5. Write the planning statement last, so it reports what the technical work found.

Biodiversity net gain is worth a specific check. The gain condition applies to most planning permissions in England, with exemptions including development that affects below the de minimis habitat threshold, so a conversion inside an existing footprint may qualify. Do not assume it. Confirm the position with the authority before you programme the application, because the biodiversity gain plan has to be approved before development starts.

If you are also adding height, the evidence base grows again, and the article on the reports needed to add storeys to an existing block sets out what changes.

This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

You can enter a postcode on PlanScope to see which reports a conversion site is likely to need before you commission anything.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.