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How to replace a roof without losing the character of the historic building beneath it

The poor state of Bodmin Jail's local natural slate roof left its Cornish custodians with a dilemma

In association with
Twelve Architects' redevelopment of grade II listed 18th-century Bodmin Jail included the specification of SSQ Riverstone phyllite slates and Velux glazing panels.
Twelve Architects' redevelopment of grade II listed 18th-century Bodmin Jail included the specification of SSQ Riverstone phyllite slates and Velux glazing panels.

How do you maintain the period character of a structure that was originally fitted with an indigenous slate roof that is now well past its prime and needs replacing?

That was the dilemma faced by the custodians of Cornwall’s Bodmin Jail.

They wanted a roofing product that could emulate the aesthetics of the 600x300mm dry-laid Cornish slate that made up the original roof, but that was more readily available.

That led them to consider SSQ’s Riverstone Ultra phyllite - both for its similarity to Cornish indigenous slates Delabole and Trevillet in terms of its strength, colour and geological profile and for its long track record of being approved by Cornwall Council’s Historic Environment and Planning Team

The slates were laid using a 200mm gauge. They were copper nailed twice onto 500x200mm factory-grade treated counter battens, which were fixed to a ply roofing deck using a Permavent Apex Air breather felt.

The finished result was a roof that had been seamlessly integrated with the modern design of the renovated buildings’ roof structure in a way that protected the centuries-old building underneath and honoured its historic aesthetics.

Find more on this case study at ssqgroup.com/case-studies/bodmin-jail

  • SSQ describes phyllite as the diamond of the slate world. It is harder, denser and stronger than any of the alternatives.
    SSQ describes phyllite as the diamond of the slate world. It is harder, denser and stronger than any of the alternatives.
  • Bodmin Jail was originally built by military engineer John Call in 1779. The buildings in their current form were completed by 1881.
    Bodmin Jail was originally built by military engineer John Call in 1779. The buildings in their current form were completed by 1881.
  • SSQ Riverstone phyllite offers architects a distinctive green-grey sheen finish for their roofing projects.
    SSQ Riverstone phyllite offers architects a distinctive green-grey sheen finish for their roofing projects.
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For more information and technical support, visit ssqgroup.com

 

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