The right conversion depends on the roof you start with. Most Hammersmith houses are two- and three-storey Victorian terraces with a pitched rear slope, and the workhorse solution is a rear dormer set into that back slope to win a bedroom and bathroom without touching the street elevation. On an end-of-terrace or semi-detached house a hip-to-gable move can square off the roof and add real width first, with the dormer behind it; on a flatter or parapet-fronted terrace a mansard may be the only form that yields a full storey. Rooflight conversions keep the roof shape and raise the fewest planning questions but add the least head height, so they suit a roof that already has the ridge height to spare. We match the option to your specific roof and to what the planning position for the address will support, rather than to a template, because the same house can carry very different schemes depending on which slope faces the street.
Whether a loft is worth doing usually comes down to head height under the ridge. As a rule of thumb you want roughly 2.2 to 2.4 metres from ceiling joist to ridge before the new floor and ceiling build-up eats into it, and the finished room has to hold a usable height across enough of its footprint to earn the disruption and the cost. The steeper Victorian roofs on Hammersmith's larger terraces often convert well; the narrow artisan cottages of Brackenbury Village and some of the split period houses carry lower ridges, and there the pitch and ridge height decide whether you gain a proper room or an awkward space you can only stand up in along the centre line. We survey the roof void and set the finished floor and ceiling levels early, so the head height is a measured figure rather than an optimistic assumption that unravels once the structure goes in.
The new staircase is the part owners most often underestimate. It has to rise from the floor 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 on the storey beneath. On a narrow Victorian terrace that floor plate is already tight, so the stair position frequently decides whether the conversion is feasible at all and how much it costs the room below, and a poorly placed flight can waste more space than the loft gains. Where the top storey is a flat or maisonette carved out of a period house, there are no permitted-development rights at all, the roof void may sit outside your demise, and the freeholder's consent and a lease check come before any design of the space above. We resolve the stair line, and the ownership question where the property is a flat, at feasibility.
Fire escape is the requirement that catches people out. Turning a two-storey house into a three-storey one 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 opening off it, and mains-powered, interlinked smoke alarms. Victorian terraces with open-plan ground floors, or a through-lounge knocked into one room, often cannot enclose the stair cleanly, so an alternative such as a sprinkler or mist system, or a compliant secondary means of escape, has to be designed in from the start. We build the escape strategy into the drawings at the outset and coordinate it with the stair enclosure, rather than letting building control reshape the scheme late and force changes that ripple back through the layout below.
A converted roof needs new structure. Typically that means steel beams spanning the house to carry the new floor and the altered roof, bearing onto the existing walls, with changes to the ridge, purlins and rafters that a structural engineer designs and calculates against the loads. On a terrace those beams almost always bear into the party walls shared with the houses on either side, which engages the Party Wall etc. Act 1996 — building on the line of junction, or excavating within three or six metres of a neighbour's structure, triggers notices to both neighbours before work starts and should be programmed early so it does not stall the build. The roof is also where the building's insulation is upgraded to current standards, so the build-up is designed to meet building regs for structure, fire, insulation and ventilation without quietly stealing the head height you are converting for.
In a conservation setting the deciding question is how the new roof reads. A rear dormer is kept subordinate — set down from the ridge, held in from the party walls and slated or clad to sit quietly against the existing slope — while a mansard works best where it can be concealed behind a parapet so the street elevation barely changes. Changes to a front or street-facing slope, and any bulky addition on the low roofs of Brackenbury Village or the listed houses around St Peter's Square, are the hardest to justify and the most likely to draw a refusal or a neighbour objection. We design the dormer or mansard to the character of the specific street and roof, check the conservation and Article 4 position for the exact address, and then set the case out in the planning drawings and a supporting statement rather than leaving the scale to be argued on site once the scaffold is already up.
