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The emergence of cross-laminated timber in the construction industry

In the move towards sustainable construction, timber and wood-based products are becoming increasingly important structural materials. Architects and builders are more and more considering mass timber to be used in larger, more complex structures both for its architectural qualities and for its potential to help decarbonize the building sector.

 

What is mass timber?

Mass timber or ‘massive timber’ is a generic term used to describe any building or structural system that uses wood, other than ‘light’ wood or ‘stick-framing’. It is composed of layers of wood joined together to form strong panels or beams. There are different types of mass timber such as the glue-laminated (glulam) beams and laminated veneer lumber (LVL) but the most common and most familiar product used in the construction industry is cross-laminated timber (CLT). With the industry shifting away from concrete-based construction, cross-laminated timber (CLT) panel products are considered as economic and more sustainable alternatives to traditional materials.

 

Advantages of cross-laminated timber

Similar to plywood, CLT is an engineered wood product that is comprised of layers of timber glued together with the grain running in opposite 90⁰ angles. It has been praised in the construction industry for its sustainability, efficiency, strength and durability.

3 main benefits of using CLT in combination with steel and other building materials:  

  • Strength
    Despite being five times lighter than concrete, CLT’s perpendicular layers make it stable and strong in two directions. CLT panels have comparable strength per weight ratio to concrete which has enabled an increase in high-rise all-timber constructions.
    Additionally, they offer excellent thermal, seismic, fire, and acoustic performance, adding exceptional protection and dependability.
  • Versatility
    CLT can be used in several applications, from walls to floors and roofing. It can be used in conjunction with other building materials such as steel and concrete to offer additional support and allow for creative and flexible architectural designs.
  • Sustainability
    CLT has a low environmental impact since it is made out of renewable wood. Compare to other commonly used building materials, it sequesters carbon and does not require the burning of fossil fuels during production,  it also produces very little onsite waste and any waste that is produced can be reused or recycled for other purposes.

Engineered timber is commonly used in combination with steel and concrete materials in many of the high-res buildings all over Western Australia on a commercial scale, as well as for residential projects. Most mass timber projects have hybrid structural systems, which contribute to their cost-effectiveness. Projects often combine mass timber floors and ceilings with light-wood-frame walls or steel seismic frames for greater economy or introduce steel-and-concrete core elements where they make sense for cost and structural efficiency.

 

Passive Fire Protection (PFP) systems for CLT Buildings

While not always recognised as a viable structural material, structural timber has inherent fire-resistant properties and when used in compliance with the NCC requirements, it becomes a good material for both mid and high-rise buildings. 

Australia’s National Construction Code (NCC) guidelines define performance requirements for buildings exposed to fire. All building work (new construction, additions and alterations or change of use of a building) must comply with these requirements to facilitate the safe evacuation of building occupants and minimise the damage to other properties. There are specific requirements that Australian architects and specifiers must bear in mind when designing timber-structured buildings:

  • Fire penetrations and C3.15 – All service openings in walls and ceilings must be sealed to prevent the fire from spreading through the building.  Each CLT manufacturer requires a suite of testing that is specific to their CLT product.  Fire stopping materials to seal service penetrations of the building such as fire pillows, fire batts, fire mortar, fire mastic, fire collars and other fire sealant products are essential to a complete passive fire protection plan in timber structured buildings.

 

  • Fire protection system for CLT floor plates and structural elements.  Floor plates are required to be tested to AS 1530: Part 4, and depending on the required FRL might incorporate fire rated plasterboard to achieve higher FRL’s.  CLT structural elements often have steel connection plates- these also need to be tested to AS 1530: Part 4 and AS4100 in relation to the protection of steel structures – Structural steel frames (columns and beams) used in combination with cross-laminated floors must be protected from fire to preserve the structural adequacy of the steel structure.
    This can be achieved using intumescent paint, spray coatings (vermiculite spray) or fire rated boards systems.

     

Case studies:

In recent years, hybrid steel-timber structures are seeing increasing use in modern building construction at a competitive price.

The application of mass timber products like CLT in harmony with steel and concrete for major construction projects can help increase site efficiency, improve sustainability, reduce capital and construction costs, enhance site safety, and improve project ROI.

 
Westralia Square

Consisting of a 12-story premium office tower and podium revitalisation, the new Westralia Tower II is a steel-framed structure with CLT floor plates. The hybrid timber and steel frame building is utilising cross laminated timber flooring, glue-laminated timber beams, steel frame core and V braced columns. Building weight was minimised and concrete largely eliminated except for one small plant room floor.

Developer: GDI Property Group

Builder: Built

Passive Fire Protection supplier: Progressive Materials

For this project, the following Promat products are being used on site:

  • Cafco 300 for steel protection – approx. 7,500m2
    CAFCO® 300 is the most cost-effective vermiculite spray product on the market.
    It is a lightweight coating that provides very efficient fire resistance with minimal thickness to structural steel.
    – Structural Steel Protection of up to 240 minutes
    – Economical. Produces high yield with low density
    – Can be used in conjunction with accelerators for faster curing time and efficient density
    – Can be applied directly on bare steel
    – Compatible with most primers if required
    – Low material cost, efficient thicknesses.
    – 0% ozone-depleting raw materials.
    – Produces a monolithic coating
    – Direct spray application

 

  • Fire Penetrations:

    Promaseal Bulkhead Batt

    It is the most economical and simplest of all fire stopping products to install. Tested up to 180 minutes with service penetrations and ideal for office buildings where cables such as computer and telecommunication cables are continuously added, removed or replaced.

    Promaseal A Acrylic Sealant

    Water based acrylic sealant designed for the sealing of joints and services penetrations against the spread of fire, smoke and hot gases for up to 240 minutes fire protection. In addition, PROMASEAL® A Acrylic Sealant may be used as acoustic sealant due to its density and flexibility.Promaseal Retrofit Fire Collars
    Promat’s range of retrofit fire collars are used around pipes and service after the services penetrations have been installed into the building. Wrapped around the already installed pipes and pushed tight to the substrate, they are designed to stop heat, smoke, fire and gas moving between compartments of the building.Promaseal SupaWrap
    It provides effective integrity and insulation for highly conductive cable trays, as they pass through plasterboard and masonry walls. Tested for up to 2 hours, it can be used in conjunction with PROMASEAL® Bulkhead Batt.


Perth’s Murdoch University, New Academic Building (NAB) 

Over 130 metres long,the four-storey New Academic Building (NAB) will add 15,000 square metres of learning space, including informal areas, as well as academic workplaces. The project is set to become the largest mass timber construction in Western Australia.

Client: Murdoch University 

Builder: Multiplex

Passive Fire Protection supplier: Progressive Materials

For this project, the following Promat products are being used on site:

  • Cafco 300 and intumescent paint to steel connection plates
  • Promat Retrofit Fire Collars for plastic pipe penetrations 

28 Mar 2022