A credible feasibility study begins with information that a neighbourhood profile cannot supply. A measured survey records the ridge, eaves, pitches, purlins, chimneys, ceilings and the floor below; the title and lease identify ownership; council mapping establishes the planning authority and designations; and the planning history can reveal conditions or earlier roof decisions. That evidence determines whether the useful comparison is a rooflight layout, a rear enlargement, a hip alteration or no viable additional storey. A similar-looking conversion nearby is context, not a transferable permission or a structural survey. It may concern a different property type, sit outside a conservation boundary, pre-date current policy or rely on rights that this house does not possess. For the same reason, Kew, TW9 or proximity to the Gardens cannot stand in for an address check. The design brief follows the verified constraints rather than using local character as a substitute for them.
There is no statutory rule saying that an unconverted roof must begin with 2.2 or 2.4 metres beneath the ridge. The useful question is how much finished headroom and floor area remain after a new structural floor, insulation, finishes and the chosen roof construction have been accounted for. The stair then adds its own geometry. Approved Document K normally illustrates 2 metres of clear headroom over a stair. For a loft conversion where that cannot be achieved, paragraph 1.13 and Diagram 1.4 show reduced headroom of 1.9 metres at the centre line and 1.8 metres at the edge. Those figures concern the stair, not a universal minimum ridge height or a promise that the room will be comfortable. We draw a section through the measured building early so that standing zones, furniture, doors, the landing and any bathroom can be tested in finished dimensions before an enlargement is assumed.
The planning route and the architectural option are related but not identical. On a qualifying dwellinghouse outside article 2(3) land, a rear enlargement may fit Class B if every limit and condition is satisfied; a rooflight alteration is considered under Class C. Within a conservation area or the World Heritage Site, Class B is unavailable, although that does not by itself decide whether a planning application will succeed or whether a separate Class C alteration remains possible. Richmond's 2015 SPD says hip-to-gable alterations are not desirable and will not be encouraged, especially where roofscape, spacing or symmetry with a paired house matters. That is a policy warning, not wording that every hip-to-gable proposal is legally impossible. The same SPD discourages front roof extensions, normally resists raising the ridge and expects a roof addition not to dominate the original roof. Each option therefore needs a route-specific and design-specific conclusion.
For a heritage-sensitive Kew roof, visibility and the contribution of the existing form matter more than a generic label such as conservation dormer. The Kew Village Planning Guidance records pitched roofs, gables, chimneys, roof coverings and repeated house rhythms as character features in particular areas, and identifies large box dormers on Bushwood Road as out of character with the roof form. That observation is not a borough-wide ban or a precedent for every street. The roof should be assessed against the appraisal and character area that actually apply. Where an alteration is supportable, the 2015 SPD favours a composition that stays below the ridge, leaves meaningful roof around a dormer, uses complementary materials and limits visually disruptive rooflights. If the address relates to the Kew World Heritage Site, its buffer, a registered landscape or an important public view, the assessment must explain the real effect on significance rather than merely naming those designations.
The stair is usually the point where the roof proposal meets the existing home. Approved Document K gives the rise, going, pitch, landing, guarding and headroom framework for a private stair; the measured plan decides where that flight can start and what it displaces. A stair might take part of a bedroom, alter a landing or require a different room arrangement, but none of those outcomes should be asserted before the survey. Its top landing also has to work with the usable-height zone in the loft, while its lower route must be coordinated with the fire strategy. Drawing a dormer first and inserting a stair later can create a large-looking floor plan that cannot be reached safely or that sacrifices the room below. We therefore test the vertical section and circulation at the same time as the proposed roof envelope, then compare options on the net accommodation they provide rather than the gross outline of the roof addition.
Fire guidance depends on the resulting building and cannot be reduced to a stock promise about one door type or a mist system. For a house, Approved Document B Section 2 paragraph 2.21 applies where a loft conversion creates a new storey above 4.5 metres: the full escape route should be addressed, with fire-resisting doors of at least E 20 and partitions of at least REI 30, including upgrading existing doors where necessary. The note to that paragraph says an open-plan layout should have new partitions enclosing the escape route. Paragraph 2.23 gives a specific alternative only when all its elements are provided: sprinkler protection to the open-plan areas; an REI 30 partition and E 20 door separating the ground storey from upper storeys while allowing loft occupants access to a first-storey escape window; and REI 30 separation of cooking facilities. A sprinkler or water-mist installation on its own is not the stated alternative. A flat or building containing flats needs the separate Section 3 and building-control assessment. Building control should agree any different engineered solution.
The new floor and altered roof need a verified load path. Approved Document A provides the structural framework, while a structural engineer should assess the existing walls, roof members, foundations and any proposed timber or steel elements. It is unsafe to assume that beams will bear into both party walls, that a ridge beam is always required or that a neighbour on each side must receive notice. The Party Wall etc. Act applies to defined work: the government's booklet gives cutting into a party wall for a beam bearing as one loft-conversion example, and other provisions may engage if a party wall is raised or qualifying excavation is proposed. The design and ownership establish the relevant adjoining owners and notice route. The Act is separate from planning and building regulations, and an agreement or award is not an architectural approval. Establishing the structure early allows the ceiling below, chimneys, services, sound separation and construction sequence to be coordinated without inventing a standard solution.
Building regulations approval is normally required for a loft conversion even when planning permission is not. Beyond stairs, fire and structure, the drawings may need to address thermal performance under Approved Document L, ventilation, drainage, electrical work, sound separation, guarding and weathering according to the actual scope. Insulation thickness and continuity are especially important to the section because they compete with internal space and must control condensation and thermal bridging; the answer varies with whether insulation sits between, below or above retained rafters and with the chosen roof finish. Historic England's guidance is relevant where an older or listed building requires more careful treatment of fabric and significance, but it does not replace the statutory tests. For a flat or maisonette, building control does not resolve roof ownership or landlord consent. For a listed building, planning permission does not replace listed building consent where the character test is met. These workstreams should be identified together and programmed without implying that one approval guarantees another.
