Norman & Underwood

18 July 2003
Leicester Lead Experts Help Restore Salisbury Cathedral To Its Former Glory

A team of experts from Leicester roof restoration specialists Norman and Underwood battled against 90 mph winds to replace protective sheeting at Salisbury Cathedral. But in just 20 weeks, the firm's craftsmen would restore the lead roofs of the cathedral's North Transept, North Choir and North Choir Aisles.

Over its 775 year history, Salisbury Cathedral has needed extensive repair and restoration work. Great names, such as Sir Christopher Wren, have advised on necessary repairs, but no recent craftsmen have been as innovative as Norman and Underwood’s specialists during the company’s recent repair of the cathedral’s lead roof.

Work on the cathedral was commissioned because the original roof fixings were no longer adequate to support the weight of the existing lead sheeting, resulting in the lead panels slipping down the steep roof slopes.

This major contract required eight of the firm’s most experienced roofing craftsmen, working on the roof’s lead, existing boarding and timberwork.

More than 150 tonnes of lead were stripped from the roof – including all lead flashings to the perimeter of the gutter and wall abutments. Craftsmen gained access to the roof via aluminium crawler ladders and safety harnesses.

Lead stripping started with the gutters so that the architect could inspect the gutter boards and associated woodwork. The roof slopes were then stripped, starting at the top, with the old lead lowered down manually to gutter level and placed onto scaffolding.

All the old lead from Salisbury Cathedral was taken to Norman and Underwood's Leicester headquarters for traditional re-casting then returned to the roofing team in re-cast form, maintaining important continuity.

The method for replacing lead on historic roofs has not changed significantly since Roman times. The process involves pouring molten lead onto a large sand-filled table. Sharp, white sand is used to allow the steam generated by the molten lead to move through the sand bed, while pulverised red moulding sand holds the grains of sharp sand together.

A bar of wood with a handle at each end – called a strickle – is used to ram and solidify the sand bed and to plane it off to the required level. The surface is then smoothed and solidified using hand-held copper planes.

Molten lead is ladled from a crucible into a steel head pan. A long handle is then lowered, which rotates an overhead wheel. This in turn lifts the head pan and shoots the molten lead down the sand bed. Whilst the molten lead is still running, the strickle is moved down the length of the table to plane the molten lead off to the required thickness. The sand bed is then totally re-made and dampened for each new cast of lead.

Before laying the metal roof, an assessment of the timber is carried out. Surveying the oak work of the various roofs prior to determining the repair strategy enabled good use to be made of state-of-the-art micro boring equipment, which helped Norman and Underwood to measure the condition and structural stability of the cathedral's 16th century oak timbers.

It was a requirement of the contract that the internal roof space to the nave remain open to visitors so a movable arched tunnel was designed by the company to protect the public. Norman and Underwood's knowledge and experience of this type of contract strengthened the company's decision to use a temporary protective sheeting technique during the work.

This decision proved to be the right one when stormy weather and high winds struck. Although the storm caused some damage to the temporary sheeting, the damage was nothing like the potential harm which could have been sustained to an entire false roof.

To minimise any possible damage to the cathedral and to ensure that the main timbers did not get wet, Norman and Underwood's emergency call out team reacted swiftly. The team put polythene in the roof space of the North Transept and Aisle roofs and monitored the cathedral throughout the night.

Although the team was able to react swiftly to protect the inside of the building, it could not get onto the roof because of gusting 90mph winds. The temporary sheeting was replaced the following day after the storm subsided.

This was not the first time that the company’s craftsmen had rushed to save the cathedral’s graceful beauty. The company has previously re-cast and re-laid the lead to the North Porch and North Aisle roofs of the cathedral.

Norman and Underwood’s efforts and skill are restoring the lead roofs of England’s most visited cathedral to their former glory, as famously captured in the paintings of John Constable.

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