There was no heating of any sort; in the winter, temperatures often fell below freezing point and the staff could only work there for a quarter of an hour at a time. Humidity exceeding 90 per cent was common, whereas documents, for safe preservation, require a maximum relative humidity of not more than 55 per cent.
The House of Lords' Offices Committee passed a unanimous resolution declaring that the necessary work should proceed as a matter of urgency. It requested the Ministry of Works to install air-conditioning within the repository rooms, in order to prevent the growth of mould on the records, besides constructing two new lifts.
The Ministry, on undertaking to fulfil these requests, discovered that the architect Charles Barry had left the Tower seriously over-loaded, and that in order to re-establish the stability of the Tower, extensive rebuilding was necessary.
It proved essential, in particular, to remove the entire internal structure from half of the Tower, to transfer the 276 tons weight of the roof from the central cast-iron pillars to the outer walls, and to construct seven new lightweight floors in the upper part of the Tower.
In the lower part, the existing five floors were completely re-designed, with the eight cell-like rooms on each floor being replaced by a single circular chamber surrounding the central staircase. A sequence of air-conditioning plants, new steel racking, a firebreak floor, and smoke-detectors were also installed.
The Tower now contained 12 floors covering 32,400 sq ft and was equipped with about 5.5m (8.9km) of steel shelving capable of accommodating approximately 24,000 cubic ft of records. The work was completed in October 1962, and the reconstructed Tower was declared open by Viscount Hailsham, Leader of the House of Lords, on 3 July 1963.