Hill House Box
Helensburgh, Scotland

A structural steel enclosure surrounding Charles Rennie Mackintosh's Hill House, Helensburgh, which will allow vital conservation works to take place without closing the building to the public.

The metal sheeted roof shelters the Grade A listed house from rain, while the chain mail mesh on the elevations allows the wind to help dry the building; stopping most rain entering the enclosure except in very windy conditions.

The roof is supported on a series of trussed portal frames spanning over the house, designed so that they were built on the ground then lifted into place in one piece. The portals provided lateral stability during construction with a pattern of diagonal bracing in the roof and elevations, which limits deflections and distributes lateral loads around the perimeter of the enclosure. Walkways integrated into the structure and a bridge over the top of the house allow visitors to view the conservation work in progress within the enclosure, while the virtually transparent mesh maintains the external views from the house over the Clyde estuary.

The key concept was to use structural steel rather than a more conventional scaffold structure to remove the need for frequent inspections and to reduce the number of structural elements to a minimum. The "Big Box" also encloses a visitor centre placed over the original entrance driveway. This structure uses engineered timber to provide a cosy shop, café and roof terrace and provides a precise modern contrast to the rough cast render exterior of the historic building.

Completed 2019.

Project Information


National Trust for Scotland


Carmody Groarke




Johan Dehlin


RIAS Award 2021
RIBA Award 2021