The right conversion depends entirely on the roof you start with, and Chiswick's stock gives you two common starting points. A Victorian terrace usually has a pitched rear slope that can take a box dormer to lift head height across the back of the plan, while an Edwardian semi more often carries a hipped roof where a hip-to-gable move squares off the side and opens real floor area before a rear dormer is added over it. Where the rear pitch is shallow, or the property sits somewhere a dormer would be resisted, a rooflight conversion that keeps the existing roof shape may be the only route, adding the least head height but raising the fewest planning questions. Many of these houses also have a lower back-addition roof, and an L-shaped dormer that steps over both the main slope and the return can add a bathroom where the plan would otherwise be too tight. We match the option to your actual roof rather than to a template.
Head height is what decides whether a loft is worth doing at all. As a working rule you want roughly 2.2 to 2.4 metres under the existing ridge before the new floor build-up, held across enough of the footprint to be a usable room rather than a strip you can only stand up in down the centre. Many Chiswick terraces have steep Victorian pitches that convert well, but a shallow rear addition roof, or a later flattened pitch, can leave you short. The finished floor build-up and the insulation layer both eat into that figure, so the height measured on site is not the height you end up with in the room. We measure the ridge and the pitch at feasibility, because that single dimension governs whether you gain a full bedroom or an awkward space with sloped ceilings closing in, and it is far cheaper to establish it before drawings than after.
The new staircase is the part owners most often underestimate, and on a terraced Chiswick house it is frequently the hardest thing to resolve. 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 eats into a bedroom or landing on the storey beneath. On a narrow two-up-two-down plan the space simply may not exist without sacrificing a room, so we fix the stair position first — it governs both the cost to the floor below and whether the roof is genuinely worth converting once you count what you lose to reach it. The alignment matters too: a loft stair that lands neatly over the existing flight keeps the plan legible and the structure simpler, whereas a stair pushed off-line to save a bedroom can force awkward beams and a compromised landing. We test the options in section before anything is fixed.
Fire escape is the requirement that catches people out. Turning a two-storey house into three lifts the 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. Many Chiswick houses have been opened up at ground floor over the years, and an open-plan hall or through-lounge cannot enclose the stair cleanly, so an alternative such as a sprinkler or mist system, or a compliant secondary escape, is designed in. We build that strategy into the drawings from the outset rather than letting building control reshape the scheme late.
A converted roof needs new structure, and this is where the party-wall relationship comes in. Typically the new floor sits on steel beams spanning the house and bearing onto the flank walls, with alterations to the ridge, purlins and rafters that a structural engineer designs and calculates. On a Chiswick terrace or semi those beams usually bear into the party walls shared with the neighbours on either side, which engages the Party Wall etc. Act 1996, so notices go out before work starts. The roof is also where the house's insulation is brought up to current standards, which on a period property means detailing the warm-roof build-up so it does not steal the head height you measured for in the first place. Where the beams land in a shared flank wall, their exact position and the padstones beneath them are part of the party-wall information the neighbours' surveyor will want to see, so we coordinate the structural design and the notices together rather than in sequence, which keeps the programme intact.
In a conservation area the deciding question is how the new roof reads from outside. A rear dormer is generally kept subordinate — set down from the ridge, in from the sides, and clad or slated to sit quietly against the existing slope — so it barely registers from the street; a hip-to-gable on a semi has to respect the pattern of the pair and the adjoining roofs. Anything on a front or street-facing slope, and prominent additions in a closely protected setting like Bedford Park, are the hardest to justify. We design the roof addition to the character of the specific street, then set out the case in the planning drawings and any supporting heritage statement. The materials carry a lot of that argument: a dormer cheek clad in slate or lead to echo the roof, with the glazing proportioned to the windows below rather than maximised, reads as part of the house rather than an addition bolted onto it, and that quiet subordination is usually what a case officer is looking for.
