The initial record is administrative as well as architectural. We run the complete postcode through the national council finder, locate the premises on the planning register and record the planning unit shown by available decisions. This matters because the familiar name Greenwich spans a lived neighbourhood rather than defining a legal planning boundary. The resulting file should contain the correct authority, relevant history, current policy status and mapped designations before a preferred roof form is drawn. A neighbour's dormer is useful visual context, but it cannot establish rights for the subject house: it may have been consented under a different policy, built as permitted development, relate to a different roof, or pre-date the records available online. Planning history is evidence to interpret, not a catalogue from which an approval can be copied.
We next establish what the owner legally occupies. A house used as one dwelling, a maisonette, an upper flat and a converted building containing several flats are not interchangeable for planning purposes. National Part 1 rights attach to qualifying dwellinghouses, not to flats or maisonettes. That exclusion governs the householder permitted-development route; it does not mean that every internal rearrangement inside a flat is external development. Title and lease questions sit alongside this classification but answer something else: the demise may or may not include the roof void, external covering, structure or route for a new stair. We identify the public-planning unit and the private ownership position separately so neither is used as a shortcut for the other.
Policy needs a dated hierarchy. At 11 August 2026, Royal Greenwich's adopted borough plan is the 2014 Core Strategy with Detailed Policies, used with the London Plan 2021 and relevant adopted supplementary guidance. A replacement Local Plan is at Regulation 19 consultation between 27 July and 6 September 2026. Its publication is significant emerging context, but it is not yet the adopted development plan. For domestic roof work, the current local design reference is the Urban Design Guide Supplementary Planning Document adopted on 18 October 2023. The accompanying adoption statement says that its household chapters supersede the former Residential Extensions, Basements and Conversions Guidance SPD. Our design note records these statuses instead of blending superseded advice, adopted policy and a consulted draft into one undated rulebook.
Physical feasibility comes from a section through measured construction. The survey records floor-to-ridge height, eaves, slopes, hips, parapets, chimneys, purlins, trusses, ceiling levels and the landing below, insofar as those elements can be observed. We then draw the proposed structural floor, insulation zone, ceiling finish and roof build-up to locate genuinely usable space. There is no national building-regulations starting height of 2.2 or 2.4 metres for an unconverted loft. Royal Greenwich's Urban Design Guide instead offers a local planning-quality benchmark: 2.1 metres of headroom across at least 11.5 square metres for a double bedroom or 7.5 square metres for a single, where the width of the highest portion of the room is at least 2.15 metres. Those figures inform accommodation quality in planning assessment; they are not a statutory room-height rule or a guarantee that a particular roof can be enlarged.
Royal Greenwich's adopted guidance provides a useful sequence for choosing the visible roof treatment. Sloping rooflights are generally accepted in design terms when they remain integrated with the roof and are aligned with windows below. A rear dormer can be acceptable depending on the building typology. The guide gives a general composition of at least 0.5 metres below the ridge, 0.5 metres in from the party walls and 0.5 metres above the eaves. These offsets are local design guidance rather than the complete Class B legal test, and the document itself leaves room for typology-specific judgement. Whichever route applies, the dormer should complement the main roof and read as a secondary element. We draw the retained roof around the addition explicitly so a nominal set-back does not disguise an over-scaled box.
Some roof forms receive a clearer warning in the same guide. Full-width box dormers are discouraged. A side dormer and rear dormer should stay visually separate rather than joining as a wraparound mass, and the document states that an L-shaped roof extension carried over an outrigger will be refused. Royal Greenwich also says it generally does not support hip-to-gable conversions because they can unbalance the host or paired composition and appear overbearing. The guide expects the existing ridge not to be raised. These passages are material local planning guidance, not amendments to national permitted-development legislation, so we cite the relevant paragraph and show how it relates to the actual typology. An option appraisal may consequently compare a smaller rear element, rooflights or retention of the hip rather than presenting maximum volume as the only useful outcome.
Heritage context changes how that roof guidance is applied, but only after the mapped asset has been identified. In a conservation area, the guide discourages new front mansards and front dormers; an exception depends on an established feature characteristic of that place. A rear dormer may also be unsupported where the building typology makes it harmful. Mansards are presented as appropriate only where they form part of established character and the roof is concealed behind a parapet, with the addition set back from both front and rear walls. Across a terrace, continuity of the ridge remains important. We therefore document parapets, party-wall upstands, chimneys, repeated roof profiles and public visibility rather than labelling a product a conservation dormer and assuming the label settles design quality.
The Maritime Greenwich designation requires an equally precise map check. The council's own page describes the historic town centre and the whole of Greenwich Park within the World Heritage Site, while its buffer includes the East Greenwich, West Greenwich and Blackheath conservation areas. UNESCO publishes the inscribed-property and buffer boundaries. An SE10 address outside a relevant mapped or evidenced relationship is not treated as though it sits inside the World Heritage property. Where the roof does relate to the property, buffer or an important setting, the submission explains the affected attribute, the verified view and the degree of change. That is more useful than a generic claim that all roof work near the park or river is sensitive, and it lets a modest alteration be assessed on its actual effect.
For a house that retains the right, Class B of the General Permitted Development Order is tested as a single set of limitations and conditions. The additional roof-space allowance is 40 cubic metres for a terraced house and 50 cubic metres for any other house; earlier enlargement of the original roof counts towards that allowance. The work cannot make any part of the dwellinghouse higher than the highest part of the existing roof. Nor may it project beyond the plane of the existing roof slope that forms the principal elevation and fronts a highway. Class B does not operate on article 2(3) land, including conservation areas and land within a World Heritage Site. Compliance with volume alone is therefore insufficient, and a planning condition or address-specific Article 4 direction may remove a right that otherwise appears available.
Rooflights and other alterations that do not enlarge the roof are considered under Class C, with that class's own limits and conditions. They should not be folded into Class B merely because both concern a loft project. Where the evidence supports a permitted-development route, a proposed lawful development certificate offers a formal council determination on the described operation; it does not confer planning permission or decide building regulations. If permission is required, Royal Greenwich's 2025 validation list helps identify the application type and baseline information. Plans, roof elevations, sections, site photographs, ownership certificates and heritage evidence are selected for the real proposal. Government guidance identifies eight weeks as the statutory limit for a valid householder or other non-major planning application unless a longer period is agreed in writing. Survey, option design and validation precede that period, while other consents and conditions can extend the overall programme; the deadline never promises approval.
The staircase is resolved in three dimensions before the room schedule is fixed. Approved Document K addresses pitch, rise, going, landings, guarding and clear headroom. The normal stair-headroom provision is 2 metres. Where a loft conversion cannot achieve it, the document illustrates a constrained alternative of 1.9 metres over the centre line and 1.8 metres at the edge. These dimensions apply above the stair, not across the proposed bedroom and not beneath every point of the existing ridge. We test several stair origins against the landing below, the path through the converted storey and the retained rooms. One option may take floor area from a bedroom; another may require a landing adjustment; a third may fail because the arrival point is under the slope. The selected arrangement follows measured consequences rather than a claim that every Greenwich terrace loses the same room area.
Fire design turns on the building after conversion, including the measured height of the new upper storey. For a house, the specific loft provisions in Approved Document B Section 2 paragraphs 2.21 and 2.23 become relevant when the conversion creates a storey more than 4.5 metres above ground level. The escape route, fire-resisting enclosure, doors, detection and final exit then need a coordinated proposal. The open-plan alternative in paragraph 2.23 is a complete three-part arrangement: sprinkler protection to the open-plan areas; REI 30 separation with an E 20 door between the ground and upper storeys while retaining first-storey escape-window access; and REI 30 enclosure of cooking facilities. A sprinkler, water-mist system or escape window by itself is not that published package. Buildings containing flats are assessed under the separate Section 3 framework and with building control; an outline page cannot select an engineered solution for them.
Structural design follows a traced load path, not a standard beam diagram. The engineer considers the existing walls, floors, roof members, chimney structure and foundations together with the proposed openings and new loading under Approved Document A. Timber, steel or a combined scheme may be appropriate, and support might be internal, external or shared, depending on evidence. The Party Wall etc. Act becomes relevant only where the designed work falls within its defined categories. Cutting a pocket into a party wall for a beam bearing is a familiar notifiable example; raising a party wall or certain excavations can engage other provisions. A loft label does not prove that both party walls will carry beams, that owners on two sides must receive notices or that a dispute and award are inevitable. We identify the actual operation and adjoining ownership after the engineer's strategy is known.
Energy and moisture performance also alter the available section. Approved Document L sets outcomes for conservation of fuel and power, but it does not prescribe one universal insulation build-up for every retained rafter or historic roof. Thickness, conductivity, continuity, thermal bridges, ventilation and condensation risk are coordinated with the roof covering and internal finish. The building-regulations package may additionally address sound between dwellings, ventilation, drainage, electrical safety, guarding, windows and weathering according to scope. Planning drawings and building-control drawings therefore answer overlapping but distinct questions: the former explain the external development and policy context, while the latter demonstrate technical compliance at the chosen stage. Permission under one regime cannot be quoted as approval under the other.
Listed and leasehold projects need their own evidence gates before invasive design is commissioned. The National Heritage List confirms statutory designation, but the list entry is not an exhaustive schedule of everything protected. For a listed building, the legal question is whether demolition, alteration or extension would affect its character as a building of special architectural or historic interest. The roof frame, covering, stair position or internal plan may be significant, yet that conclusion must come from the building rather than from its age. In a flat or maisonette, the lease and title determine whether the roof void is demised and what landlord, freeholder or management-company approval is required. LEASE advises checking the actual wording because a lease may permit, condition or prohibit alterations. Listed-building consent, landlord consent and planning are not substitutes for one another.
A coordinated project brief records decisions in an order that limits abortive work: verify the address and planning unit; map conservation, World Heritage, Article 4 and listing records; measure the roof and floor below; compare accommodation and roof-form options; agree the planning route; then develop stair, fire, structure and fabric detail with the relevant specialists. Cost advice follows the same evidence. A compact rooflight layout, a rear dormer requiring permission and a heritage-led mansard do not carry one dependable neighbourhood price. We define the drawings, application support and consultant inputs in writing, identify council and third-party charges separately, and distinguish design fees from construction cost. This produces an auditable route for the specific home without predicting a consent decision or concealing unresolved survey information behind a fixed typology.
