A decorative roof and curved weathered-steel wall will enclose the Amersham Vent Shaft that Grimshaw has designed for the High Speed Two railway.

Built within a road junction in the town of Amersham, England, the cylindrical headhouse will become one of the only visible elements of the rail line’s 10-mile-long tunnel through the Chilterns countryside.

Its curvaceous, sculpture-like aesthetic has been developed by British architecture practice Grimshaw to become a “local landmark” and pay homage to the rolling hills around the site.

Amersham Vent Shaft is one of the five headhouses that will be built above the Chiltern tunnel to provide emergency access and ventilation.

Once complete, the centrepiece of the Amersham Vent Shaft will be the headhouse’s roof, which marks the top of the 18-metre-deep ventilation shaft.

Viewable from a distance, this roof will be capped by aluminium fins that are hoped to disguise the building and soften its visual impact.

“Behind the screen, the conical headhouse shows the shape and location of the circular ventilation shaft below,” explained Patience.

“The top of the building is crowned by an array of anodised aluminium fins, set out to respond to the shape of the surrounding valley and longer distance views.”

The headhouse will sit off-centre within the weathered-steel wall, which Grimshaw has incorporated to mark the perimeter of the site. This wall will sit on top of flint-filled gabions and unfold to reveal a gated entrance.

Weathering steel was chosen by Grimshaw for the boundary wall as it complements “the natural tones” of the surrounding landscape and will help reduce the project’s visual impact further.