ing layer or plywood spline is provided. Similar to a plywood spline between CLT panels, this continuous layer prevents air movement between floors, thus ensuring char development remains uni-directional (NLT Guide 3.3.2). The local authority having jurisdiction (AHJ) for the T3 building accepted permanent gaps between NLT panels for this reason.
DLT can be used in all types of combustible construction. From a fire perspective, DLT behaves the same or better than NLT.
Both the National Building Code of Canada (NBCC) and the IBC recognize NLT and provide guidance for both structural and fire design. No product-specific standard is required, as the structural design of each lamination element is covered by the building codes. It is resistant to fire, and has long met the requirements of heavy timber in North American building codes. NLT can be used in all types of combustible construction.
The fire resistance of mass timber panels is now widely proven – the char developed during a fire creates a self-protection layer. Research recently completed by FPInnovations showed that a 2 x 8 NLT floor panel with concrete topping can achieve a three-hour fire resistance rating under full load (Osborne, 2015).
The inherent fire performance of mass timber removes the need for intumescent coatings and dropped ceilings that would be required for a steel structure, allowing the wood to be exposed as a permanent soffit.
As with all mass timber systems, it is important to address acoustic separation between mass timber walls and floors, which can be achieved through appropriate detailing. Acoustic mat should be used in floor buildups with no dropped ceiling.
Timber-Concrete Composites with DLT
The stiffness of mass timber panels is important in long-span floor systems, and as can be seen in Table 1, consideration of floor vibrations often govern the required panel thickness.
A concrete topping is often required for acoustic performance, and this topping can be made composite with DLT panels to increase the panel stiffness. In Europe, many different techniques of creating composite action between the DLT and the concrete topping are used, including:
• Fully threaded screws inclined in the direction of the shear flow
• Milled notches in the DLT panel, continuous perpendicular to the direction of the span
• Use of fluted DLT, with the flutes turned up so the concrete topping flows between the higher laminations
Dowel Laminated Timber takes mass timber construction one step further to create a 100 per cent wood panel which can be CNC machined and incorporate acoustic treatment into an exposed wood soffit. Due to its efficiency, aesthetics, and cost effectiveness, DLT will help lead the push towards wood construction.
DLT also extends the range of mass timber options available in North America, and supports the trend towards prefabrication as the future of building construction.
• Binational Softwood Lumber Council. 2017.
Nail Laminated Timber – U.S. and Canadian Design and Construction Guide v1.0.
• E3 Berlin, www.proholz.at/zuschnitt/33/lueckenfueller-mit-distanz
• Osborne, Linday (FPInnovations). 2015.
“Fire Resistance of Long Span Composite
Wood-Concrete Floor Systems”
Lucas Epp, P.Eng., leads the engineering department at StructureCraft and has also co-authored industry guidelines including the recently published NLT Design and Construction Guide. He can be reached at email@example.com or (604) 313-2526.