The Fulham Victorian terrace roof is, in most cases, a "London roof" — a butterfly or M-shaped design in which two slopes pitch inwards towards a central valley gutter hidden behind a front parapet wall. Seen from the street it reads as a flat-topped facade, but behind that parapet the roof drains internally rather than shedding water to the front. This arrangement shapes almost every roofing decision on these streets, from leak repairs to loft conversions.
What is a London roof?
A London roof, also called a butterfly roof, has two pitched slopes that rise from a shared central channel and fall away towards the front and rear of the property. The profile is a shallow V or M when viewed end-on, the opposite of a conventional double-pitched roof that sheds outwards. The design suited tightly packed terraces because it kept the street elevation low and uniform behind a decorative parapet.
In Fulham this form is near-universal on the late nineteenth-century terraces around the area. The front slope often sits behind a brick parapet topped with coping stones, while the rear slope drops towards the garden. Materials are typically natural or Welsh slate on the visible pitches, with the valley itself lined in lead or, in later repairs, a single-ply membrane or felt.
Why the central valley gutter is the weak point
Seen from the street it reads as a flat-topped facade, but behind that parapet the roof drains internally rather than shedding water to the front.
The central valley gutter is where rainwater from both slopes collects before being carried away, usually through an internal or rear downpipe. Because it sits at the lowest point and handles the whole roof's run-off, it is the first place to fail. Standing water, leaf debris, and the limited fall of a long gutter all add stress to the lining.
Lead remains the traditional lining, but lead expands and contracts with temperature, and joints that are too long or poorly lapped can split. When the valley leaks, water enters above the ceilings of the upper floors rather than running off the outside, so damage can spread before it is noticed. Common issues a surveyor will check include:
- Splits or fatigue cracks in lead, often at joints that exceed recommended bay lengths.
- Blocked or undersized outlets and downpipes, causing ponding and overflow back into the building.
- Failed mortar at the parapet and coping, letting water track behind the gutter.
- Patched felt or membrane repairs laid over old lead, which can trap moisture.
Access is the other complication. The valley sits between two roofs behind a parapet, so inspection and repair usually require scaffolding or a roof ladder, and party-wall considerations may apply where a valley is shared between neighbours.
Rear additions: flat roofs over kitchen extensions
Most Fulham terraces have a rear "closet wing" or a later ground-floor extension running into the garden, and these are typically covered by a flat roof. The original coverings were often felt; many have since been replaced with single-ply membranes, glass-reinforced plastic (GRP), or, occasionally, lead or zinc. A flat roof should have a slight fall to a defined drainage point, even where it looks level from below.
Flat roofs over kitchen extensions tend to age faster than the main slate roof and are a frequent source of leaks. Where an extension abuts the main rear wall, the junction between the flat roof and the brickwork — the upstand and flashing — is the detail most worth examining. Rooflights and lantern roofs, popular on kitchen extensions in the area, add further joints that need careful weathering.
How a loft conversion reshapes the roof
Loft conversions are common across Fulham's terraces and almost always alter the butterfly roofline. The usual approach is a rear dormer built into the back slope, which adds headroom while leaving the parapet-fronted street elevation largely unchanged — an important point given the conservation areas and Article 4 directions that apply to parts of the borough.
A dormer changes how water moves across the roof, so the valley gutter, the dormer cheeks, and the new flat or pitched dormer roof all have to be integrated with the existing slate and lead. Planning rules in Hammersmith and Fulham restrict alterations visible from the street, and a mansard or a raised ridge may require full planning permission rather than permitted development. Anyone planning a conversion should confirm the local position and check that the existing valley can still drain freely once the roof geometry has changed.