The right conversion depends on the roof you start with, and Greenwich offers three broad starting points. Where a Georgian terrace near the town centre or Croom's Hill conceals a shallow roof behind a parapet, that can suit a mansard or a set-back dormer kept below the parapet line so the street elevation barely changes. On a Victorian or Italianate villa around Maze Hill or Westcombe Park with a steeper hipped roof, a hip-to-gable move or a rear dormer set into the back slope opens genuine floor area. Where a later terrace on the borough's slopes has a pitched back-addition roof, it is often suited to a rear dormer, sometimes combined with rooflights to the front to keep the street elevation intact. The three roof types carry very different planning risks and very different structural implications, so the first job is to identify honestly which one you have and what the wider setting will bear. We match the option to your roof rather than to a template.
Whether a loft is worth doing usually comes down to head height under the existing ridge. As a rule of thumb you want roughly 2.2 to 2.4 metres before the new floor build-up, held across enough of the footprint to be usable rather than a space you can only stand up in along the centre. A steeper-pitched villa roof around Maze Hill or Westcombe Park often converts well; a shallower parapet roof on a Georgian terrace can yield less without a mansard that reshapes the roof. A back-addition or outrigger roof can also complicate the geometry, since the usable area often sits in the main roof while the stair has to negotiate the join between the two. We measure the ridge height and pitch at survey, and set out where the headroom actually falls, so the decision to convert is made on the real roof rather than on optimism.
The new staircase is the part owners most often underestimate. It has to rise from the storey below within the going and rise limits of Approved Document K and land with full headroom over it, and it almost always consumes part of a bedroom or landing beneath. On a narrow Georgian terrace, or in a converted period flat where the plan is already fixed and tight, the stair frequently decides whether the roof space is worth converting at all. Retaining the existing stair's line to keep the enclosure continuous often makes the fire strategy simpler, but the geometry does not always allow it, and a space-saving stair has its own limits under the regulations. We resolve its position at feasibility, because it governs both the cost to the floor below and whether the usable area gained upstairs justifies the room lost beneath.
Means of escape is the requirement that catches Greenwich owners out. Turning a two-storey house into three lifts the new top floor above the 4.5-metre threshold and triggers a higher standard: a protected stair enclosure running all the way to a final exit, fire-rated doors — typically FD30 — to the habitable rooms off it, and mains-powered, interlinked smoke alarms. Period Greenwich houses with knocked-through or open-plan lower floors often cannot enclose the stair cleanly, so an alternative such as a sprinkler or mist system, or a compliant secondary escape, is designed in. Window sizing for emergency egress and rescue also enters the picture, and on a conservation roof that has to be reconciled with how the dormer or rooflight is allowed to look. We build the escape strategy into the drawings from the outset rather than letting building control reshape the scheme late.
A converted roof needs new structure. Typically that means steel beams spanning the house and bearing onto the existing walls, with alterations to the ridge, purlins and rafters that a structural engineer designs and calculates. On the terraces and the semi-detached villas those beams usually bear into the party walls shared with neighbours on either side, which engages the Party Wall etc. Act 1996 — notices go to the adjoining owners before work starts, separately from the planning decision. The roof is also where the building's insulation is upgraded to current standards, which on a shallow roof competes directly with the head height you are trying to preserve, so the build-up is detailed carefully. In a converted period flat the ownership of the roof space itself and the freeholder's structural interest have to be settled first, before any of the structural design is worth commissioning.
In the conservation and World Heritage setting the deciding question is how the new roof reads in the wider view. A rear dormer is kept subordinate — set down from the ridge, in from the sides, and slated or clad to sit quietly against the existing slope; a mansard on a Georgian terrace works best concealed behind the parapet. Changes to a front or river- or park-facing slope, and prominent additions on a villa's designed roof, are the hardest to justify given the sensitivity near the World Heritage Site. We design the roofscape to the character of the specific street, then set out the case in the planning drawings and any heritage justification the application needs. Materials matter as much as form: natural slate or a matching tile, lead or zinc to a dormer cheek, and glazing kept modest all help an addition recede rather than announce itself against the protected skyline.
