Grand Entrance for UC4 Glulam

A new school auditorium for Horris Hill Preparatory School on its rural campus near Newbury, Berkshire, has been transformed using structural engineered timber and a Use Class 4 (UC4) treated glulam portico.

The choice of materials for the new David Brownlow theatre at Horris Hill School was driven by three main concerns – context, sustainability and affordability. These were all delivered through the specification of a primary structure made from PEFC-certified spruce cross laminated timber (CLT) and a specially treated pine external glulam portico from Piveteaubois, that frames the building’s primary entrance to the school.

The theatre is an intimate performance space seating up to 160 people and the timber-lined interior provides an appropriate backdrop to the drama that will be enjoyed by both the school and wider community. Eurban were appointed as specialist timber engineers and subcontractors to carry out the design, supply and assembly of the new theatre’s CLT and glulam superstructure, after being approached by Johnathan Tuckey Design in 2016 for early specialist input on the engineered timber aspects of the project.

A unique aspect of the building is the glulam portico. This ‘playful’ structure is taller than the building and echoes the diagonal lines of the red wood fibre cement cladding panels. It is a sculptural element creating a dramatic threshold to the new theatre. The building consists of 7.56m3 of UC4 impregnated pine GL24h glulam beams – both TANALITH and TANATONE treated – and supplied by leading French timber supplier Piveteaubois.

The timber was treated and processed at Piveteaubois’ factory in Sainte Florence, France, before being shipped to site. The process used to produce UC4 treated glulam beams, firstly sees each layer of pine, moisture controlled before an initial high pressure TANALITH treatment to UC4 requirements. The layers are then kiln dried in preparation for the glue lamination process to create the finished beams. Once laminated, the glulam beams are then given a further careful low-pressure treatment (low pressure helps to avoid potential de-lamination issues).Finally, the beams are machined and cut to length according to the project design.

This treatment means that structural elements can withstand harsh climates and provides a long-lasting solution for outdoor use in areas of high humidity. UC4 pine treated glulam is suitable for use in service class 3 applications and is guaranteed for 20 years for use above ground.

UC4 treated pine has been used in France for decades, with Piveteaubois pioneering the impregnation of pine to UC4 in France with the installation of its first autoclaves in 1984, to develop the use of softwood for outdoor use and timber frame buildings. Currently Piveteaubois treats over 120,000m3 of pine products to UC4 annually under its DURAPIN flagship brand, including 10,000m3 of glulam.

“Our CTB-B+ Certified UC4 treated pine is the only certified UC4 pine glulam available on the market today,” says Elisabeth Piveteau-Boley, Director UK & Ireland at Piveteaubois. “It was the perfect solution for the Horris School portico and a great showcase for using UC4 treated glulam in the UK. It looks fantastic and the finished building has real impact and importantly superb durability. It was a great project to be involved with and we are really happy to hear that the staff and students love it as well.”

You can read the full feature in the Winter Timber Construction magazine

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