Replacing Roofing Materials on Buildings of National Importance

by Kate Hancock, Burton Roofing Merchants Ltd

LIKELY TO BE the oldest and least altered part of a historic building, the roof is often the most original part and the first stage in any historic roof work is to observe and record what is there. Traditional roofing materials including stone, slate, clay, copper, lead, and mortar mixes all combine with the detail, style and the structure of the roof to make it unique.

Matching details

An understanding of what is already there is essential when there’s a need to replace roofing materials on buildings of historic importance. Natural England state the emphasis should always be on matching details appropriate for the locality and age of the building.

The fact that a historic roof has survived for so long is a testimony to the design, materials and craftsperson’s skill. Whilst it might be tempting to introduce modern products, it’s important not to dilute regional distinctiveness and replicate the roof as closely as possible, allowing it to continue to perform for centuries to come.

An example is the heritage roofing work currently taking place at Wentworth Woodhouse. Built between 1725 and 1750 and Grade I listed, the mansion was purchased for £7million by the Wentworth Woodhouse Preservation Trust in 2017, following a five-year campaign with SAVE.

Its Grade I listed stables and riding school were built from 1766 and the riding school roof is being repaired as part of a major restoration project undertaken by Aura Conservation who specialise heritage restoration and builds. The company’s Contract Manager Dave Anderson recently invited Burton Roofing Merchants to visit the prestigious project and witness how our roofing materials are being used.

The slate roof is being replaced ‘like for like’ with Burlington Slate from Cumbria. Quality slates probably have an indefinite life, but once the roof starts to suffer, whether it be the loss of pegs or ‘nail tiredness’ it’s better to strip and re-nail it. Whilst battens and nails would have originally been attached with oak pegs, today, unless the pegs are still in existence, broad-shanked copper nails are often an acceptable alternative.

Heritage skills

Even the best materials lose their character if they are used without understanding and skill and it’s essential that heritage work is carried out by true craftspeople.

Aura’s team are shaping and holing the slate on site using traditional tools including the bench iron and slaters axes. It’s estimated 75% of the original slate can be salvaged and wherever possible the old slate will be reused elsewhere on the roof.

Slates can be supplied in a sized format (fixed lengths with random widths) which help to retain a traditional random element to the roof design, whilst speeding up the laying process to reduce installation costs.

Roof timbers were made of English oak and pitch pine. The latter is used to waterproof ships because the sap produced by the timber acts as waterproofing. Felt would obviously not have been in use when the main house was originally roofed in 1720. Its evidence reveals that sections have been re-roofed fairly recently.

Over the last 100 years, some species of UK bat have now come to rely predominantly on man-made structures for shelter and roosting. Natural England always specifies 1F bitumen felt underlay. Simple to install and heavy enough to help prevent wind uplift, the traditional Hessian weave 1F felt is still manufactured in virtually the same way as it was 100 years ago. Even when no bats are thought to be present, a modern breather membrane is considered a potentially fatal future trap bats can get tangled in, but the 1F felt has a rough surface bats can grip onto.

Working with the Bat Conservation Trust, Burton Roofing Merchants has a national press campaign to raise awareness of the decline in the bat population and more information is available on our website.

Click here to read more about the roof work at Wentworth Woodhouse.

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