We poured the last section of our level 4 slab at Junction House yesterday. As I was leaving the site, I tweeted this photo out from Watkinson Avenue. What you are seeing is the northwest corner of the building where we have seven two-storey towns that front onto our rear laneway. In response to this tweet, Andrew Williamson asked a most excellent question: "timber next?"

My response was that we would love to do a mass timber building. We have certainly looked at it in the past, and we will continue to look for opportunities to use more sustainable building materials wherever possible. But there are challenges to overcome and a project like Junction House would have been far more difficult to do in mass timber. I'm not an expert when it comes to wood construction, but I will offer up three items that have come up for us in the past.

The first is trade familiarity. We are in a highly inflationary hard cost environment right now. Everyone is hyper focused on costs and the market is competitive. So switching to a construction method that is less common comes with some additional risks. But this will almost certainly change over time as the market evolves and more people adopt mass timber.

The second is water. The Junction area, or at least parts of it, have a relatively high water table. That is certainly the case with our site. One of the things you need to do during construction is dewater, or draw down the water level within your site so that you can actually build. In our case, we built a watertight below-grade parking structure, though that isn't always the case.

Dewatering comes at a cost and so generally you want to stop dewatering as soon as it is feasible to do so. But you need to make sure that you have enough weight to counteract the buoyancy forces associated with groundwater returning to the site. Generally this means you need to wait until you've finished constructing a certain level in the building so that there's enough mass. The engineers will say things, "we can shut off the dewatering once we complete our level 4 slab."

The thing to consider with all of this is that concrete is heavier than wood, which means that you may need to run your dewatering program for longer (increasing your costs). Or, if your building isn't all that big, maybe you'll never have enough weight to offset the below-grade water forces and so you have to look at other methods for keeping your building from floating away. Again, this will increase your costs.

The last thing I'll mention is that mass timber buildings generally have higher floor-to-floor heights compared to cast-in-place concrete. What this means is that a 9 storey building in timber is going to be taller, in meters, compared to a 9 storey building in concrete -- even if the clear heights within the suites are the same. This is a massive deal when you're operating in an environment that is highly sensitive to building height.

In the case of Junction House, we were negotiating our final height in centimeter increments -- literally arguing whether it could be 50cm to 1.3m taller than some perceived maximum height. This is, in my mind, absurd, but it became a hill that people were willing to die on. The result is that our laneway towns (pictured above) went from having an entrance that was a few steps up off the lane to having an entrance that is now a few steps down off the lane. That is how we ultimately solved our centimeter problem.

This wounded me to my core because, at the end of the day, what are people going to remark: The additional meter at the top of the building or the relationship that these towns will now have to the street? It will, of course, be the latter. So please know that our hearts were in the right place. But what this also means is that had we been trying to build in wood, we likely would have lost a floor during this negotiation and that would have killed the entire project.

Over the past few years there’s been growing interest in using mass timber for high-rise buildings (now colloquially referred to as “plyscrapers”).

One project that got a lot of attention last year is Brock Commons (student residence) at the University of British Columbia. It is an 18-storey hybrid mass timber tower.

The first and second floor (slab) and the two cores are poured-in-place concrete. After that, the other 16 floors of the tower consist of 5-ply cross laminated timber (CLT) panels and glue laminated timber (glulam) columns running every 10 feet. The roof is steel and metal decking.

Below is a great time lapse video of the building under construction once it had switched over to timber. The wood construction portion started on June 6, 2016 and finished on August 10, 2016. So 2 floors per week.

The video is well-annotated so that you know what week of construction it is, how many wood installers are on-site, which structural members are going in (along with their dimensions), and so on. The CLT panels are only 169mm thick.