Loft
conversions
in Marlow, SL7
Designers, Architects, Engineers & Builders Under One Roof.
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Whether a Marlow loft can be converted without a planning application turns on two boundaries, the conservation area and the Chilterns National Landscape, and then on the shape of the roof itself.
Roofs in the old town vary a good deal. The End House on the High Street has a mansard of old tiles, the Borlase Cottages on Chapel Street share one long tiled roof over a two-storey terrace, and a West Street house of two storeys and attic already carries a modern dormer, according to the council's Historic Environment Record.
Space is the usual reason. In the Marlow ward, 32.8 per cent of households had three bedrooms at the 2021 Census and 21.8 per cent two, and a loft room adds one without enlarging the footprint, which matters near the river, where the district's flood assessment discourages extensions.
Sources: Buckinghamshire Council Heritage Portal (Historic Environment Record): The End House, High Street, Marlow (MBC19884); Buckinghamshire Council Heritage Portal (Historic Environment Record): Borlase Cottages, Chapel Street, Marlow (MBC19843); Buckinghamshire Council Heritage Portal (Historic Environment Record): West Street, Marlow (MBC19937); ONS/Nomis: Census 2021 TS050 Number of bedrooms, 2022 ward Marlow (E05013153); Wycombe District Council: Strategic Flood Risk Assessment Level 1 Update (November 2014)
When a Marlow loft needs planning permission
Class B of the householder permitted development rights governs roof additions, and it does not apply at all to a house on article 2(3) land. Conservation areas and areas of outstanding natural beauty are both such land: in Marlow, that means the conservation area round the centre and the Chilterns National Landscape on the northern edge.
Outside both, Class B lets the roof space grow by no more than 40 cubic metres on a terrace house and 50 on any other, with no part of the house rising above the highest part of the existing roof and nothing projecting beyond a front roof slope that faces a highway.
Its conditions add that exterior materials must look like those of the house, and that any window in a side wall or side roof slope must be obscure-glazed.
For a house in the Green Belt, a dormer adds volume, and the DM43 test on our Wycombe page compares the resulting building with the original, meaning the building as it existed on 1 July 1948.
Sources: legislation.gov.uk: GPDO 2015 (SI 2015/596), Schedule 2 Part 1, development within the curtilage of a dwellinghouse (latest available revised); legislation.gov.uk: Town and Country Planning (General Permitted Development) (England) Order 2015 (SI 2015/596), article 2 (latest available revised); legislation.gov.uk: GPDO 2015 (SI 2015/596), Schedule 1 Part 1, Article 2(3) land (latest available revised); planning.data.gov.uk (MHCLG): conservation area point query 51.5707,-0.7756 (Marlow centre); planning.data.gov.uk (MHCLG, Natural England data): AONB point query 51.585,-0.785 (north edge of Marlow); Wycombe District Council: Wycombe District Local Plan (adopted August 2019)
Hipped, mansard and terrace roofs
The council's records show how varied the old town's roofs are: a late eighteenth-century High Street house under a hipped roof of old tiles, the End House's mansard, and the Borlase Cottages with offset eaves over chequer brick. A hipped roof gives less headroom under the ridge than a gable, and in a listed building or the conservation area any reshaping of it is a matter for planning permission or listed building consent.
Where Class B does apply, a dormer other than a hip-to-gable change must keep or reinstate the original eaves and sit, so far as practicable, at least 0.2 metres back from them, and no Class B addition may include a verandah, balcony or raised platform.
On the northern slopes the plan's concern is the longer view. For the housing site it allocated at Seymour Court Road, inside the Chilterns, it asked for a landscape and visual impact assessment, particularly in relation to longer distance views, and protecting the landscape setting of the town is one of its principles for Marlow.
So we photograph a roof from the pavement, the garden and, on rising ground, from further off, and test dormer sizes against those views before a drawing goes anywhere near the council.
Sources: Buckinghamshire Council Heritage Portal (Historic Environment Record): High Street, Marlow (MBC19874); Buckinghamshire Council Heritage Portal (Historic Environment Record): The End House, High Street, Marlow (MBC19884); Buckinghamshire Council Heritage Portal (Historic Environment Record): Borlase Cottages, Chapel Street, Marlow (MBC19843); legislation.gov.uk: GPDO 2015 (SI 2015/596), Schedule 2 Part 1, development within the curtilage of a dwellinghouse (latest available revised); legislation.gov.uk (The National Archives): Planning (Listed Buildings and Conservation Areas) Act 1990, section 7 (restriction on works affecting listed buildings); Wycombe District Council: Wycombe District Local Plan (adopted August 2019)
Escape routes and the new floor
Once a converted loft puts a floor above 4.5m, Approved Document B deals with the whole route out of the house rather than the new room alone. Doors along it become fire-resisting to at least E 20 and partitions to REI 30, with existing doors upgraded where needed.
An open-plan ground floor needs new partitions around the escape route. The alternative is sprinklers to the open-plan areas, a fire-resisting partition and door separating the ground storey from the floors above, and cooking walled off from the open space.
When a two-storey house gains a third storey, the new floor needs at least REI 30, and smoke alarms are mains operated. Doors of historical or architectural merit are looked at for retention and upgrading before anyone replaces them.
Steel, chimneys and the house next door
Cutting into a party wall to take the bearing of a beam is the government's own loft conversion example of notifiable work, and removing a chimney from a party wall is notifiable too. Semi-detached and terraced houses made up 23.1 and 23.4 per cent of the ward's households in 2021, so in many conversions the notices are planned with the steel.
Party wall agreements are separate from planning permission and from building regulations approval. Sign-off for the conversion comes from Buckinghamshire Council's building control service, or from a private registered building control approver who notifies the council by an initial notice.
Where an application is needed, Buckinghamshire Council decides it and asks Marlow Town Council for its view; the town council can comment on loss of privacy, which a rear dormer's windows can raise.
Our London team designs the conversion from the Finchley Road studio in Hampstead, with in-house architects and designers for the room and roof, our structural engineers for the floor and steel, and Hampstead Chartered Surveyors & Building Consultancy for the measured survey.
On a semi we look at the other half's roof first: a matching dormer next door, or a hip already turned into a gable, shows how the pair has been altered before and what the new work has to line up with.
The roof is opened from the scaffold under a sheeted cover, and the hole for the new stair is made through the landing ceiling as one of the last structural steps; until then the bedrooms below are lived in as normal.
Outside Marlow, and in London rather than Buckinghamshire: Project example: Belsize Park, NW3. That project of ours included a loft conversion, sympathetic to the house, on a Victorian townhouse of five storeys, with its basement and rear extension alongside, as its case study describes.
Sources: GOV.UK: The Party Wall etc. Act 1996 explanatory booklet; GOV.UK: Party walls and building work (printable guide); ONS/Nomis: Census 2021 TS044 Accommodation type, 2022 ward Marlow (E05013153); Buckinghamshire Council: Building regulations and control; GOV.UK: Building regulations approval (printable guide); Buckinghamshire Council: Local Development Scheme, 3. Our current plans and documents (last updated 16 March 2026); Marlow Town Council: Planning & Transport Committee; Hampstead Renovations: Belsize Park Gardens, NW3 case study
Loft Conversions in Marlow: Questions
Can I convert my Marlow loft under permitted development inside the Chilterns National Landscape?
Not if the roof changes shape. Class B, the householder right for roof additions, does not apply on article 2(3) land, which includes areas of outstanding natural beauty such as the Chilterns, so a dormer there needs planning permission. A point on Marlow's northern edge lies inside the Chilterns while the centre does not, so the answer depends on the address.
What fire safety work does a loft conversion in a Marlow house need?
Where the new storey is above 4.5m, the whole escape route is addressed: fire-resisting doors of at least E 20 and partitions of REI 30, existing doors upgraded where necessary and partitions enclosing the route through any open-plan space, unless sprinklers and a fire-resisting separation at ground storey are used instead. The new floor needs REI 30 at least and smoke alarms run off the mains.
Do I need a party wall notice for a loft conversion in Marlow?
If the new steel bears on the party wall with the adjoining house, or a chimney is taken out of that wall, yes: both are notifiable under the party wall rules. A detached house may need none. The party wall process runs alongside planning and building control and is separate from both.
Who signs off building regulations for a loft conversion in Marlow?
Buckinghamshire Council's building control service, or a private registered building control approver you appoint instead, who then serves the council an initial notice. We send the fire strategy and the engineer's floor design to whichever you choose and book its inspections.
What do you look at first when visiting a Marlow loft?
The pitch and height of the roof, the headroom where a stair could arrive, any chimneys, tanks and purlins in the way, and how the roof reads from the street and the garden. We also confirm whether listing, the conservation area or the Chilterns boundary applies to the house, because those three answers settle the planning route.
Can the attic of a listed house in Marlow be converted?
Sometimes. The route is listed building consent, since works touching a listed building's special interest have to be authorised. Attics are not new to the town's listed stock: the council's records describe a High Street house of three storeys, attic and cellar, and a West Street house of two storeys and attic with a modern dormer. We design around the existing roof structure rather than replacing it.
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