Concrete vs. CLT
June 12, 2017•News
A building material with a long-standing history in construction, mass timber is recognized as being a durable and sustainable building option. Most commonly known as cross-laminated timber, or CLT, structures using mass timber have made their mark on projects around the globe, from London to Vancouver. Its popularity comes from the material being as durable as concrete, but with a smaller lifecycle price tag, leading construction companies to save money during the building process. Unlike its concrete competitor, building with CLT means job sites are safer and timelines are met faster, whether building a multi-family residence or commercial building.
A reliable building material
When it comes to construction, it is important for materials to be able to stand the test of time. Companies need to know they are using materials that are reliable, durable and have longevity. While for many years concrete and steel were thought to be the two competing options, the use of mass timber dates back to well before the 7th century.
Despite being five-times lighter than concrete, CLT has comparable strength per weight ratio to concrete and the multi-layer wooden panel spans in two directions. Each layer is placed cross-wise to the adjacent layers to increase its stability and strength. Buildings using mass timber carry the same strength as concrete while minimizing cost and building time. This strength also allows modern connection engineering to dissipate seismic forces in a highly effective manner, enabling mass timber buildings to commonly outperform other systems in terms of cost and life safety in earthquake zones.
One of the biggest myths of building with CLT is that is more expensive; some incorrectly believe a specialized crew is needed for the install phase. This couldn’t be further from the truth. Buildings using cross-laminated timber are cost competitive to those built with steel and concrete.
The largest contributor to cost savings is prefabrication. Structurlam supplies mass timber packages for projects globally. Recently, we made headlines for supplying mass timber for what is now the world’s largest timber tower – UBC Brock Commons. The 18-storey tower was constructed much faster than anticipated, due in part to the prefabrication of the mass timber components. Our innovation allows us to develop 3D models of projects, so that every piece of CrossLam® CLT that will be used is modelled exactly as it will fit on site in 3D, accurate to the millimetre. Those measurements are then used to create the CrossLam® CLT panels and steel connectors for the project; materials arrive on the job site ready to be assembled like giant Lego blocks. This process cuts costs and time down by limiting what needs to be prepared on a job site. Crosslam® CLT projects are installed in a shorter period of time due to the accuracy of the pre-fab materials, making them a smart use of money for construction teams.
Prefabricated materials ensure complete coordination between design, manufacturing and on-site construction. Overall project costs are reduced because the construction schedule is shorter and materials are brought to site ready to be installed.
Faster on-site construction
Compared to concrete, CLT structures can be installed in a shorter time period. In fact, more than 15,000 square feet of CLT can be installed per day, dramatically cutting construction schedules. UBC’s Brock Commons tower rose 18-storeys in only eight weeks. This remarkable timeline was made possible because Structurlam’s prefabricated CrossLam® CLT arrived on-site ready to be installed. CLT can be directly shipped to the job site, where panels are lifted into place and secured with steel connectors. This makes it possible for larger towers to have multiple floors constructed per week. Faster construction is accompanied with safer and quieter sites; UBC Brock Commons reported zero safety incidents during the mass timber installation of the 18-storey building. Due to the pre-fabrication and seamless installation, site noise was greatly reduced allowing construction in urban areas with minimal public disturbances. Additionally, construction using CLT can proceed year-round and is not inhibited by weather.
Unlike concrete, building with mass timber has a number of environmental benefits. Life cycle assessments show that wood outperforms both steel and concrete in terms of energy, air pollution and water pollution.
Carbon storage is an important component of building with CLT. A healthy tree in a forest will release oxygen and store carbon dioxide (CO2). Using mass timber as a building product reduces the carbon footprint by also storing carbon dioxide (CO2) in the same way a healthy tree would. To put it into perspective, it is believed a single five-storey, cross-laminated timber building will cut emissions by levels equivalent to removing up to 600 cars from the road for a year.
In British Columbia, large amounts of CLT are made from Mountain Pine Beetle-kill wood. If those dead trees were to remain in the forest, they would emit CO2 into the atmosphere instead of storing it. However, if trees have already died due to pine beetle contamination, the timber is still sound and useable for construction for up to 10 years. By utilizing that wood before it goes to waste, CLT becomes a building product that not only sequesters tonnes of carbon, but also reduces greenhouse gas emissions during construction through the prefabrication process.
CLT also outperforms concrete when it comes to job site waste. Since most or all CLT panels are prefabricated, there is little to no waste on site. Manufacturers can also re-use any scraps for stairs or other architectural elements.
Looking to projects like UBC Brock Commons, it is clear that CLT is a sound investment, both financially and environmentally. Its proven strength, structural performance and cost-competitiveness means the opportunities for CLT are expanding into a wider range of buildings. From multi-family homes, industrial buildings, recreation centres, to college campus buildings, CLT is proving time and time again that it is the smart choice. Flexible, sustainable and far more efficient than concrete, CLT has changed the construction landscape and is fast becoming the go-to choice for builders.