The flat roof
Castle Drogo’s medieval-style flat roof has been its Achilles heel. Lutyens had attempted to seal the roof using asphalt, a relatively new and untested material for the time, but it was prone to cracks caused as the temperature rose and fell. Before the building was even finished, it had begun to leak.
The flat roof is roughly equivalent to two international football pitches. A high-tech roof system, designed by Bauder is being installed. This two layer membrane is designed to cope with the extremes of temperature experienced on Dartmoor.
In order to lay the new waterproof system, 2,355 granite blocks weighing 680 tonnes have to be removed and then reinstated. This will involve moving and reassembling entire battlements and large sections of the castle walls.
We have also had to redesign the roof gullies to accommodate the heavy Dartmoor rainfall.
There has been a real problem with water penetration through the pointing and around the windows. So the building will be completely repointed. The cracked cement pointing is being removed and replaced with an improved lime based mortar. The sheer amount of new pointing required stretches to an impressive 60,000 metres (laid in a line it would stretch all the way from Castle Drogo to Lundy Island).
The windows have been another major weakness for Drogo. In keeping with a medieval fortress, Julius Drewe had demanded that there were no windowsills, a feature that would have offered some protection from the fierce elements. Every one of the 913 windows will be removed, refurbished and resealed.
Proving it works
In 2007 we tested this solution on the chapel, a part of the castle badly affected by water damage. The large windows were restored and the Bauder roof system introduced, the chapel is now watertight.