Tottenham: a hand cut mansard roof six storeys up

The brief

An empty shell, and everything structural still to build

The Gladstone House project in North London started in January 2022 with a building that was an empty shell and a brief to turn it into four luxury apartments. On a conversion like that the carpentry is not a finishing trade arriving at the end. It is the first thing on site and it is structural: without floors there is nothing to stand on, and without a roof there is nothing to work under.

The building also happened to be six storeys tall, in a dense part of Tottenham, which changes the job in ways a drawing never shows. Every length of timber has to be got up there. Every cut is made at height. And the roof, when it came, had to be hand cut in place rather than craned in as a made-up structure.

The work ran through 2022 in phases: the first joist and floor set in January, a second joist set in March with the steels infilled, and in September the joist and roof set that finished the building off.

What we did

Four apartments, floors first

The first task was the joists and floors that would define the four apartments. A team of three completed that set in five days flat, working long days and early mornings to do it. On a conversion the floor set is the gate on everything behind it, so five days rather than two weeks is not a vanity statistic, it is a fortnight handed back to the programme.

Steels infilled with hand cut joists and hangers

The second joist set followed in March. By day three the team had the steel all infilled with hand cut joists on hangers, ready for boarding in 18mm marine ply.

Infilling steel is a different discipline to fitting floor joists in a new build. The steel is set out on site and there is no realistic prospect of every bay being the dimension it was drawn at, so the joists get cut to the opening that is actually there. Hangers then transfer the load into the steel properly instead of relying on timber bearing on a flange. It is slower than dropping in a pre-ordered joist run, and it is the only way of getting a floor that is flat, level and quiet in a building that was not designed around it.

The 18mm marine ply deck is a heavier specification than a standard flooring board. On a project that is going to stand open to the weather for months before it is watertight, that matters: the deck is a working platform for every trade behind you long before it is a floor.

Six storeys up: flat roof, mansard and parapet

In September 2022 the team completed another large joist and roof set, working six storeys up to hand cut and fit a flat roof, a mansard roof with three built-in dormers, and a parapet wall around the perimeter.

A mansard is the most demanding roof shape in ordinary construction. Two pitches on each side, a steep lower slope and a shallow upper one, means twice the number of critical set-out lines, and every one of them has to be right or the elevation reads as crooked from the street. The three built-in dormers sit within the steep slope, so their cheeks, trimmers and flat tops all have to be framed into a plane that is itself sloping. The parapet wall around the perimeter then hides the junction between the flat roof and the mansard, which is exactly where the water goes, so the falls and the upstands have to be set before the covering trade arrives.

All of it was hand cut in position. At that height and that geometry there is no truss solution: the roof is cut to the building.