Bespoke Savill style

A large timber gridshell canopy now floats over a corner of the royal Windsor Great Park.

Its undulating form and oak surface match the luxuriantly planted hillocks of the Savill garden where it resides, covering an expansive £5.4m visitor centre.

It may not match the classical architecture favoured by Prince Charles, but then the patron for this project was the ranger of the royal park, Prince Philip.

The roof undulates over the visitor centre Credit: Warwick Sweeney

The timber canopy is raised high above a clear-glazed window wall that offers views of the Savill Garden beyond. It was this "through vision", rather than the undulating roof, that was the initial competition-winning concept of Glenn Howells Architects. The idea of a timber gridshell emerged later, when it was reckoned to make the most efficient use of the larch and oak harvested from the park.

The gridshell roof is designed by the two firms responsible for the award-winning gridshell at the Weald & Downland Museum in West Sussex: engineer Buro Happold and the Green Oak Carpentry Company. One difference at the Savill garden is that the gridshell is raised off the ground and supported around its perimeter by a tubular steel beam. The other is that the Savill Garden's gridshell is made of cheap homegrown larch softwood, rather than oak.

That said, the construction process was very similar.

The visitor centre Credit: Warwick Sweeney

High-grade 80 × 50 mm sections of larch were pieced together with finger-joints in lengths up to 90 m. These were then laid out to cross over in a 1 m2 grid on adjustable scaffolding poles. Next, the poles were gradually lowered until the gridshell reached the desired form of three gentle domes. Finally, an upper grid of sections was laid and a layer of plywood screwed down from the top.

The timber shell visible from the outside is made of oak battens that will weather to silver grey. The plywood roof was covered with standing-seam aluminium sheeting, and the oak battens were fixed by aluminium brackets to the standing seams. This neatly avoided the problem of piercing the waterproof aluminium sheeting, thus sparing the interior below from a right royal mess.