Alnwick Castle
Case Study: Alnwick Castle
Introduction
The brainchild of the Duchess of Northumberland, the timber tree house at Alnwick Castle in Northumberland is a public restaurant with 112 covers, a large public deck/viewing gallery, a small retail outlet and two private meeting rooms all constructed from timber and located eight feet off the ground. Access to the deck is via a single ramp and at any one time there could be more than 300 people on the deck. In addition, a large children’s adventure play area was located adjacent to the tree house.
This unique structure is certainly not the type that the authors of Approved Document B or the associated British Standard 5588 had in mind when these guides were written. Therefore the design of a fire safety engineering strategy by Exova Fire Safety Consulting team in conjunction with Napper Architects and Alnwick Gardens Limited was an exciting challenge.
The Challenge
Given the novel design and proposed constructional features of the structure, it was not considered adequate to simply seek to apply the recommended design solutions contained in the various fire safety design guidance documents; Exova needed to devise a fire safety solution that complied with the functional requirements of Building Regulations while still maintaining the character and utility of the building.
The two particular aspects of this project that required the direct application of fire engineering techniques were the determination of adequate egress arrangements and the nature of the timber structure necessary to provide the necessary levels of fire protection.
The Solution
Exova undertook a detail analysis of the adequacy to the escape arrangements looking at total escape time of around seven minutes for people in the tree house. This detailed work allows for an effective fire evacuation procedure to be put in place.
With regard to structural fire protection, Exova’s research revealed that the elements of the structure should have not less than 30 minutes fire resistance when tested in accordance with BS 476, or the European equivalent. With this information the client was able to provide suitable provisions to ensure the restaurant was able to meet the requirements for fire safety.
The Results
Exova ensured Alnwick Castle complied with the functional requirements of the building regulations, whilst maintaining the character and utility of the building. The egress arrangements were adequately determined and the timber structure provided the necessary levels of fire protection.
