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Introduced by Mike Rawlins of David Brain Partnership on 14 April 1997
Mike Rawlins is an architect who has studied the vaults and their problems at length. Large parts of the centre of Bath were built on vaults to raise the bottom floor of the houses above the flood level of the River Avon. These vaults extend under the pavement and in many cases under the roadway. In effect, these roads are long bridges.
The vaults vary in size with spans from 2.1 to 5m (7ft -16ft 6in) heights from 2.4 to 3.5m (8ft -11ft 7in)and with the crown from 450 to 1100 mm (1ft 5in -3ft 8in) below the road surface. They are built of 250 mm thick (10in) rough stone walls bonded with lime mortar.
The owner or occupier has, since the Highway Act of 1980, the responsibility for maintaining them because this act abolished the Bath Acts of the 19th century and favoured road users at the expense of the owners of adjacent properties. The 1980 Act was drafted for the national road system without taking account of the special conditions in Bath, particularly the effects of the greatly increased weight and speed of modern traffic compared with the horse-drawn wagons for which the vaults were designed. This Highways Act makes local authorities responsible for maintaining bridges but vaults are not recognised as bridges!
The passage of heavy vehicles over the vaults causes vibrations throughout the houses, which may be even more damaging to the Georgian architecture of Bath than the visible damage to the vault structure, which comprises distortion of the arch shape, movement of the base on the supports and ingress of water which affects the mortar. The effect of a vehicle increases with the cube of its weight - a 40 ton lorry causes 1000 times as much damage as a 4 ton van. Vibration is caused by unevenness in the road surface, and the unevenness is made worse each time a lorry bounces over the bump or hole.
After a lively discussion it was recommended that, immediately, the Highway Authority (B&NES now) should impose and enforce a 7 tonne maximum loaded weight limit on roads over vaults. Then a campaign at Government and EU levels should draw attention to the damage being done to this World Heritage City