A contractor that has recently completed a project involving glued laminated timber has provided an insight into lessons learned from the use of this material.
The project involved using laminated timber structural beams and panels within the roof structure.
Our experience suggests the following for improving construction delivery.
- Understand the tolerances. This project saw significant deflection because of large spans between columns and a cantilevered canopy projecting beyond the facade, in some cases more than expected. Structurally it is fine, but it created challenges with interfacing details, and where water ponds.
- Ensure that valleys, gutters, and rainwater outlets are numerous and adequate because of the roof settling into position after loading.
- Make sure there is an effective weatherproof protective layer on the panels prior to the final roof finish being applied.
- Only start when the following trades are ready as excessive exposure to the elements will lead to a need to dry out the timber.
- If there are rooflights and service penetrations, having them all in the model early will be very beneficial – they can have a much more dramatic effect on the design than a steel or concrete equivalent because of how load is transferred.
- If there are feature roof structures, such as ETFE covered openings, be wary of the tension loadings as experience shows that a steel subframe is likely to be needed to cope with the loads.
- It is important to get the design model from the specialist laminated timber sub-contractor once completed so that there is no question as to the availability of this information later. The requirement should be a part of the sub-contract conditions.