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Saturday, 18 January 2014

The Problem with Cross Laminated Timber is...



ESB UBC - Great Fun: Great Contractor, Engineer and Architect.

By John Boys

The new Wunderkind and current trend-darling in commercial construction is cross laminated timber (CLT) panels. Paired with glue-lam timbers and other engineered wood products it is making possible the construction of tall wood buildings. CLT is being touted as the green alternative to concrete, the building material that makes for speedy and efficient assembly, allows for flexible and innovative design, and all at a competitive cost to conventional materials such as tilt-up concrete.

And they are all of that – or rather they could be.

UBC O - Great Design/Build Team
Our team has had more experience in the installation of CLT in North America than most, and as heavy timber specialists (with roots in log-building and timber framing) we are excited by its potential and the possibilities it affords, but concerned that if the bottom-line expectations are not realized, that this revolutionary shift in how we build may disappear before it has proved it’s potential.

On projects where we have been given sufficient time to trouble-shoot, communicate, pre-plan and sequence our part of the work we can achieve the “just-like-lego-time-lapse-look-at-em-go scenario” that we are all anticipating.  Our team thrives on the well-coordinated dance of carefully rehearsed steps, meeting or exceeding our planned schedule when we finally “go live”. Who doesn’t like to look good!
UBC-O; interesting design

But it could be even better (and not only for us), if we and some of the other key trades and/or material suppliers were allowed both information and input much earlier in the design stage. Pre-planning in isolation and extrapolating information from incomplete final plans makes it awkward to contribute any solutions other than those which address absolutely un-workable details and/or connections.

While most trades people are not engineers, nor do all of us have a flair for design, cost effective, safe and even elegant solutions at material interfaces can be achieved if we are included (as appropriate) to define logical breaks in scope of work and to consider possible challenges long before these issues come up at the construction site.

UBC-O; connections +more connections
And it is on the job site, where the success of the design and planning can be gauged and measured. Assuming that the prime contractor, heavy timber specialists and material suppliers are competent, and that the plans and specifications are well thought out, a wonderful and choreographed dance begins to take place. If any of the above fall short, there are a lot of steel toed shoes getting stepped on…

So how is any of the above a “Problem with Cross-Laminated Timber”? In reviewing my words, it reads more like a rant about not being included!

In part, it is. I believe there are two things that threaten the future use of CLT in commercial structures, the first that we are often treating a new material as a substitute to the well understood materials (such as tilt-up concrete) to which we are accustomed.

3 D modelling. Not just for architects any more! (UBC-O)
Do we anticipate the challenging characteristics of this organic material (UV, rain, snow…shrinkage, expansion, iron staining…) and the associated costs? And are we taking full advantage of the benefits (precision CNC prefabrication, light weight, high strength to weight, visual qualities, insulation...)?

What tolerances are achievable and how does that affect specifications? Do the connection methods allow us to efficiently bridge the differing tolerances? Concrete+/- 30mm, steel +/- 3 mm, wood +/- 3mm, engineered connectors +/- 1mm, glazing systems....?

Using this new material effectively, in my opinion, requires a mind-shift that addresses its individual properties as well as a re-think of how we connect with the other components of the structure, and goes back to my pre-amble on pre-planning and brings me to the second point:

Pre-planning resolves breaks in scope, discovers solutions, arrives at efficient procedures and defines what is expected of the trades and helps them to submit well considered and inclusive bids resulting in fewer change orders and realistic budgeting.  In short, pre-planning can save money and my money is on the bottom line when determining the future of CLT.

UBC O CLT: as Espressed Structure; the talents ofMcFarland-Marceau
A great deal of our inspiration for CLT in North America is derived from the success stories in Europe and the common factor in all of these examples is that all the projects were built on a foundation that incorporated sophisticated 3D modelling and that a great deal of time (and money) was spent in pre-fabrication and sequencing strategies.
3D modelling and pre-planning means a significant up-front investment. 

It also involves a radical shift in how we approach design, engineering and the bid process and it allows all of us to be accountable. I wonder if that is possible…However it seems logical and expedient, that a revolutionary new type of structure should also generate a radical change in how we work together.

In closing, the “Log Builder’s Wife” tells me she could have made the point a bit more succinctly; her quote on the topic: “We can sing Green till we are Blue in the face, but if Green equals Red, then Black will trump Green!”).

I could go on at length and in more detail on this topic, but perhaps that is better saved for another day. In the meantime, I would be interested to know if I am alone in my concerns for the future of CLT in North America. Your comments welcomed.
 
"I'd like to harp on 3D modeling a little more..."
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