Posted on November 12, 2020
There is a growing trend in multi-family residential construction to use wood as an alternative to precast concrete. The primary reason for this choice is a lower initial cost. There is no question that in most cases a wood frame structure will be cheaper to build than the equivalent in precast concrete.
However, to truly understand the price of a building, we must look beyond initial cost of construction, to the cost of ownership and the potential to create revenue, and through the building’s life cycle. When we look at all of these as a whole, precast concrete comes out on top for a multitude of reasons.
A modern total precast building is made up of large components. These components are fabricated in a facility off-site and then assembled on-site at a faster rate than a wood frame building. This minimizes disruption at the jobsite and the building can be handed over to the owner sooner. Opening a building in less time means less general overhead cost during the course of construction, which can be passed on to the owner. Not only does this make the general contractor’s price more competitive, the building will be generating revenue in less time than a wood frame building, lowering the owners construction financing cost. These very real costs are not often considered when looking at a project.
Another thing that is not often considered is the simple fact that wood burns, precast concrete does not. This has cost implications during construction and during the life cycle of the building. Course Of Construction Insurance for a wood frame building is higher than for a precast building. In addition, fewer insurance companies are willing to provide long-term insurance for wood frame buildings. Furthermore, with more fire events occurring in today's climate, the cost of this insurance is going up. In some cases, in a wood frame building with sprinklers, a fire may cause little damage. However, the water damage from the sprinklers can be bad enough to make the building uninhabitable. Obviously, a total precast building would not be affected by these issues.
There are very few places where it does not rain or snow during the course of construction. When moisture falls on wood, it soaks in, and in some cases, is trapped by the building envelope. Trapped moisture can lead to mold and structural issues resulting in very expensive mitigation. In addition, no matter how well wood is dried, it will shrink. This shrinking will lead to multiple cosmetic issues for years after construction, resulting in expensive call-backs for the general contractor and owner. Again, these are issues that do not affect a total precast building.
The exterior of a total precast building is durable, high-performance concrete, requiring virtually no maintenance over the life cycle of the building. Any cladding on a wood frame building will require maintenance or replacement during the building's life cycle.
A total precast building is also quieter to live in than a wood frame building. People are willing to pay more for a quieter place to live, generating more revenue for the equivalent space over the life of the building.
People are becoming more aware of the environmental impact of construction materials and are willing to pay more for less impact. A wood frame buildings require the stripping of large areas of land, destroying natural resources at an alarming rate. A total precast building is made using locally- sourced sand and stone, which comes from locations that have less impact on the environment. The reinforcing is made from recycled steel and the cement, which is the only energy-intensive material, is less than 6% of the concrete. At the end of the buildings life, precast can be recycled; wood cannot. Clearly, a wood frame building has a greater impact on the environment.
In conclusion precast concrete is the best choice for multi-family residential when all the costs and impacts on the environment are considered
Art Macaw, P. Eng
Team Sales Engineer