Loft
conversions
in Radlett, WD7
Designers, Architects, Engineers & Builders Under One Roof.
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Before anyone sketches a Radlett loft room we answer three questions: may this house use Class B at all, what will the council's dormer guidance accept, and how will the stair below be kept safe from fire?
Radlett's roofs vary as much as its houses. Along the High Street the neighbourhood plan describes high pitched and gabled roofs with dormer windows and decorative details, while its 2015 survey counted 108 bungalows and 63 chalet bungalows, grouped in clusters of streets where they set the character.
The plan also records concern about replacement houses with bulky, expansive crown roofs that overbear their neighbours, and its Design Code asks that ridge heights take account of gradients and respect neighbouring properties. A loft that raises or bulks out a roof meets that concern head on, so we draw the roof from the street before we draw the room.
Sources: Aldenham Parish Council / Hertsmere Borough Council: Adopted Radlett Plan 2020-2036 (low resolution)
Class B, the conservation areas and the bungalow directions
The householder roof right, Class B, is for enlarging a house through additions or alterations to the roof. Houses in conservation areas cannot use it, because those areas fall within article 2(3) land, so in Radlett North and Radlett South every dormer needs a planning application.
Elsewhere in the town, Class B lets no part of the house rise above the top of the existing roof, nor reach forward of the main front slope where that slope faces a road. It also allows a terraced house no more than 40 cubic metres of extra roof space, and other houses 50.
Outside, the new work has to use materials of similar appearance to the existing house's, a window in a side roof slope or side wall must be obscure-glazed, and a balcony or raised platform is excluded altogether.
For the bungalows named in the three Article 4 directions, the right that has gone is Class AA, the added storey. The council says it did not intend to prevent conventional loft conversions under other permitted development rights.
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); Hertsmere Borough Council: Radlett Bungalows Article 4
The dormers the council's guide will accept in Radlett
Part E of the council's Planning and Design Guide wants dormers on the rear roof slope, as small as possible and generally taking up no more than 60% of it. It will normally resist dormers in the front roof unless they are an established part of the street scene, and dormers on a side roof face as well.
A dormer should sit at least 0.3 metres below the ridge and above the eaves, and at least 0.5 metres in from the side or boundary walls, while a roof extension as wide as the house that reads as a large box will be refused. Bricks, tiles and window frames must match the original house, though a flat roof may sometimes be acceptable on a rear dormer.
Hip-to-gable conversions will normally be refused because they unbalance a house, pair or terrace, although the guide allows that re-balancing may be possible where the neighbour's half was already converted under permitted development. Large dormers nearby that were built under permitted development are not accepted as a reason to build another.
Where a conventional dormer cannot be used, the guide sees a roof light as an alternative, but several roof lights in the front roof face may themselves need planning permission.
Protecting the stair, the new floor and the shared wall in a Radlett loft
Approved Document B treats a conversion that produces a storey higher than 4.5m as a change to the whole house. The escape route must be dealt with along its full length, with E 20 as the minimum for its doors and REI 30 for its partitions, and any existing door that falls short upgraded. Where the rooms below have been opened into one space, new partitions close off the route, or the guidance's alternative is followed, which puts sprinklers into the open-plan areas.
When a two-storey house gains a storey, its new floors have to reach REI 30 at the least, and smoke alarms are to be mains powered. Before an old door of historical or architectural merit is swapped for a fire door, the guidance asks for keeping and upgrading it to be looked into.
Where the house is joined to the next one, bearing new steel into that wall or taking chimneys out of it is work the neighbour must be told about. The party wall process runs alongside planning and building control rather than inside either, so our notices are drafted alongside the drawings.
Sources: GOV.UK (MHCLG): Approved Document B (fire safety) volume 1: Dwellings, 2019 edition incorporating 2020, 2022, 2025 and 2026 amendments and forthcoming 2029 changes; GOV.UK: Party walls and building work - overview; GOV.UK: Party walls and building work - work you must tell your neighbour about
Converting a Radlett loft
Lofts in Radlett are taken on by our London team: in-house architects and designers, structural engineers for the new floor and steel, and Hampstead Chartered Surveyors & Building Consultancy for the survey. Applications go to Hertsmere Borough Council, and sign-off for the conversion comes from Hertfordshire Building Control or a private registered building control approver.
Our first measurements are the roof's pitch, the clear height under the ridge and the headroom where a new stair could arrive; in many houses the stair, not the floor area, settles the scheme.
The roof is opened only once scaffold and temporary covers are in place, the new floor sits on steel our engineer has sized, and the opening for the stair is cut from the landing near the end, so the bedrooms below stay in use.
Fire doors, alarms and the protected route are finished and inspected before the new room is plastered out and decorated.
Outside Radlett, and in London rather than Hertfordshire: 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: Hertsmere Borough Council: Hertfordshire Building Control Limited; GOV.UK: Building regulations approval - when you need approval; Hampstead Renovations: Belsize Park Gardens, NW3 case study
Loft Conversions in Radlett: Questions
Can I convert my Radlett loft under permitted development inside one of Radlett's conservation areas?
Not with a dormer. Class B, the roof additions class, is unavailable on article 2(3) land, and every conservation area falls into that category, so a dormer in Radlett North or Radlett South needs planning permission. The council's guide then applies: a small dormer on the rear slope, set well within the roof.
What fire precautions does a Radlett loft conversion call for?
If the new room sits above 4.5m, every part of the route from the loft to the front door is treated: fire-resisting doors and partitions, with old doors brought up to standard, or for an open-plan ground floor the sprinkler-based alternative. The new floor must achieve at least REI 30, and smoke alarms run off the mains.
Will my neighbour need a party wall notice for a Radlett loft?
Yes, if the house is joined to theirs and the work touches the shared wall: working on it, cutting into it for steel, or taking chimneys out of it all need notice. A detached house raises it less often, though building at the boundary still counts.
Does the Radlett Plan say anything about dormers or roof changes?
It sets principles rather than dormer dimensions. Its Design Code asks for ridge heights that take account of gradients and respect neighbouring properties, Policy HD3 requires development to respect local character and residential amenity, and Policy HD7 asks proposals affecting the identified bungalows to protect or enhance their contribution. The dormer detail comes from the council's own guide.
Which body approves the building regulations side of a Radlett loft?
Hertfordshire Building Control, or else a private registered building control approver of your choosing. Keep the completion certificate safe, because lacking approval you would be without the compliance certificates you may need for a sale.
What do you check first on a visit to a Radlett loft?
Roof pitch and height, where a stair could land, which way the joists run, chimney stacks and the water tank, and whether the address falls inside Radlett North, Radlett South or the bungalow list. Photos of the roof taken from the pavement and the garden help us judge how a dormer would sit.
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