Roofing

When fire destroyed the roof capping a turret on a grade II*-listed Victorian apartment block in Whitehall Court, London, it presented a unique specification challenge to the team that had to rebuild it.

“It had to go back in precisely the same materials using the same techniques the Victorians would have used,” explains Geoffrey Goddard, managing director of contractor Lengard.

The problem was there was little of the structure left to work out its original form. The main vertical timber posts were still in place but badly charred and the rest of the structure had burned away. The only compensation was that the remnants of the structure were still supporting the lead finial capping the turret. This was salvaged and reinstated. Engineer Knapp Hicks and Partners produced new drawings for the contractor to work from but it quickly transpired that these did not accurately represent the original structure.

Engineer, contract administrator and project manager Gross Fine and English Heritage worked with Lengard and timber specialist Constructional Timber on the recreation. Archive searches revealed the timber sections in the new drawings were far too small. Careful examination of the remnants also helped and, luckily, there was an area at the bottom of the tower that wasn’t damaged. This was exposed and the team found that timber boards were nailed at a 45° angle to help brace the structure and Westmoreland slates were nailed directly to the boards. Armed with this information, the team prepared replacement buildings so that rebuilding work could begin.

The next challenge was sourcing the right wood in large-enough sections, as the original British pitch pine was unavailable. “English Heritage specified Californian southern pitch pine but we found you couldn’t get the timber in those section sizes so we sourced long-leaf Honduras pine, which took longer,” says Goddard.

Getting the sections into position 40 m above the ground was not easy either. They were up to 406 × 203 mm, 65 ft long and weighed up to 600 kg. The timber was craned to the top of the building and dropped into position but the largest sections had to be cut in half, craned in and spliced together again.

Some modifications were made to try to bring the building up to the Building Regulations. The new slates are not fixed to battens but fixed directly to the boards, as in the original, because using battens would have changed the exterior size of the roof. A modern breathable membrane has been inserted between the slates and timber, and new insulation has been fixed between the structural timber members.

“It’s a bit of a fudge but it’s a matter of balancing conservation with the practicalities,” says Kevin Marshall, Gross Fine’s project manager. Once it is finished the residents of the two flats being inserted into the roof space won’t have any idea that the roof they are living under is brand new.