Summary
• £31m Waingels College uses cross-laminated timber, glulam and Pavatherm Plus wood fibre insulation.
• The wood fibre contributes to a wall U-value of 0.25W/m²K.
• The Woodland Trust’s award-winning new HQ uses Gutex wood fibre board in depths up to 282mm.

Pavatherm Plus wood fibre insulation from Natural Building Technologies (NBT) plays a key role in making Waingels College, in Woodley near Reading, one of the lowest carbon schools in the UK.

The new £31.1m school was part funded under the Labour government’s Building Schools for the Future (BSF) programme and was completed in October.

The team behind it were some of the foremost names in UK timber construction.

The main contractor was Wilmott Dixon, which recently completed work on the UK’s tallest residential timber structure, the eight-storey cross-laminated timber (CLT) Bridport House in London, and the architect and engineer were Sheppard Robson and Ramboll, which previously worked together on one of the UK’s biggest timber school buildings, the CLT-based Norwich Open Academy. The other key player was specialist timber contractor Eurban, while the CLT panels themselves were prefabricated at Stora Enso’s Austrian plant.

Sheppard Robson describes Waingels as “innovative in both form and construction”, comprising four separate two-storey structures which frame an open “village green” area.

The structural element of the building comprises a mix of load-bearing 135mm CLT wall, floor and ceiling panels and glue-laminated timber beams and columns. One truss in the building made from glulam is 18m long, while the CLT floor cassettes span up to 8m.

Energy efficiency

A key design aim was to make the building as energy efficient and low carbon as possible and the shell structure is claimed to provide a 60% reduction in CO2 emissions during operation over alternative construction systems, achieving a regulated energy consumption of just 42KWhr/m²/yr.

The walls are insulated with 3,815m² of Pavatherm Plus prefabricated into Pavaclad panels, which were fixed directly to the timber frame in a continuous layer. This was then overclad in heat-treated softwood on the upper storeys, with the lower storeys finished in mineral render.

According to NBT, the thermal shell created by the wood fibre reduces thermal bridging and helps achieve an external wall U-value of 0.25W/m²K and airtightness of 2.45m³/hr/m²@50Pa. The insulation also provides fabric moisture control and “overheating mitigation”.

It added that the fact that Pavtherm Plus, which is produced by Swiss manufacturer Pavatex, is breathable also reduces the risk of mould formation and contributes to a “healthy living environment”. And the material’s 95% recycled fibre content gave it an even stronger environmental hook for client and architect.

The finished building won the “best practice in UK design and construction of schools” category in this year’s British Council for School Environments Awards. It is due to be officially opened and fully in use in April.