REFURBISHMENT SPECIFIC OPPORTUNITIES

The most significant refurbishment challenges include the reuse of foundations and adaptation of existing superstructures to allow alternative uses or create additional accommodation. In addition, the buildability of proposed extensions in and around existing buildings can create logistical and viability issues especially where some areas remain occupied.

Engineered timber and CLT provides an excellent solution to these challenges, mainly due to its high strength-to-weight ratio. Consequently, strengthening of existing structures and works in the ground may also be drastically reduced. If there is a limitation on new foundations or existing below ground infrastructure restricting load-bearing capacity (such as rail tunnels, services or drainage), additional storeys can often be justified compared to alternative materials.

The lightweight nature of CLT also makes deliveries, lifting and erection much easier and significantly safer than with other materials. Panels can easily be adapted or sized to suit cranage limitations on restricted or congested sites and if a mobile crane is required erection is so quick that any associated road closures can be limited

A limitation on new build commercial timber structures is often the grid that is achievable, typically less than that expected by commercial tenants. Forming open plan floors with long spans using CLT typically requires deep beams (whatever their form) pushing the building height upwards. For refurbishments however, older buildings often have a smaller grid which must be retained, often within the span capabilities of CLT panels, meaning an extremely efficient timber structure can be used to complement existing spaces.

DESIGNING A TIMBER EXTENSION

The most common types of existing structures can be adapted and extended using full CLT, or with timber and other hybrid frame elements:

• Reinforced concrete (RC) frames – RC buildings frequently have inherent excess capacity built in and are relatively simple to extend; timber connections can be anchored into the existing structure. A survey will be required and scanning to ensure the position of the existing reinforcement is highly recommended to avoid delays on site.
  
• Steel frames – As the connection pieces for timber frames are predominantly steel, this is no different to extending using a more traditional steel construction. If the building dates from the first part of the 20th century it may have rivets on the existing beams and columns, which should be surveyed in detail prior to detailing and production of the connections.
  
• Load-bearing masonry – CLT load-bearing walls can be used to extend masonry structures in the same form but in a more lightweight fashion. The connection between the two walls, whether on top or to the side should be carefully considered. A typical method to extend upwards is with a steel shoe junction, which may require fire protection and lateral extensions can be fixed with standard timber brackets, but again will need to be considered aesthetically.