Waugh Thistleton Architects isn’t particularly interested in conjuring timber skyscrapers or extolling wood’s expressive qualities. In fact, though the London firm was the forerunner in modern residential timber towers with the 2009 completion of the nine-story Murray Grove building, its latest timber project gives little hint that it is the largest cross-laminated timber (CLT) building in the world.
Like Murray Grove, the 155,000-square-foot Dalston Works is located in the London borough of Hackney, which instituted a “timber first” policy for new construction in 2012. The latter project comprises several building volumes ranging from five to 10 stories tall that provide 121 units of housing along with office, restaurant, and retail space. Except for the building’s concrete podium, the structure is built entirely of CLT, from the floors to the walls to the elevator cores. As a result, Dalston Works weighs just one-fifth of its hypothetical concrete counterpart, an important trait given its location atop a potential Crossrail 2 station.
And yet passersby would never know. Dalston Works’ exterior is clad in brick without a square inch of wood peeking through. “It’s counterintuitive to clad a lightweight building in heavy stuff,” acknowledges project architect Dave Lomax, a senior associate at Waugh Thistleton. But normalizing mass timber construction is a priority for the firm. “We don’t think that sustainable buildings always have to be made of hay bales and have a whirligig on top that spins in the wind,” he says. “We want to develop beautiful architecture that shows no sign that it’s sustainable.”
Due to the structure’s light weight, local developer and general contractor Regal Homes was able to increase the number of housing units by 25 percent. “In real hard pounds and pence, if you have 25 percent more homes to sell, that’s going to win the debate for our clients,” Lomax says. “And that means we get our narrative: taking carbon and locking it away in our buildings, rather than pumping carbon into the atmosphere to make concrete.” Copenhagen, Denmark–based structural engineering firm Ramboll—which, along with B&K Structures in Derby, England, helped design the timber skeleton—estimates that Dalston Works sequesters 2,866 tons of carbon dioxide in its 136,000 cubic feet of CLT.
The spruce used in the CLT panels was harvested by timber supplier Binderholz, headquartered in Fügen, Austria, with forests, sawmills, and mass timber production facilities throughout Austria, Germany, and Finland. Wall panels range from 4 to 5.5 inches thick while floor slabs range from 4 to nearly 8 inches thick, with the thicker panels used on lower floors. For residential units’ interior walls and ceilings, a layer of plasterboard provides fire protection—a more economical option than beefing up the CLT—while office walls are exposed wood. On the exterior, the CLT is protected by a vapor barrier, a 4.3-inch layer of foil-faced insulation, and the brick façade.
The bricks are full-sized, not a veneer, Lomax notes, as they tend to be more aesthetically pleasing and more durable. Hackney building official also made it clear that brick veneer was not an option. Slight differentiations in the brick’s color—depending on whether the brick was fired once or twice—denote changes in program: a darker brown brick for the office tower and a warmer, redder brick for the residences. The brick is attached via stainless steel masonry support angles developed specifically for CLT. The 3.5-inch-deep angle attaches to a series of steel “shoes,” which are 10 inches tall and 5.6 inches deep and are screwed directly to the wood, Lomax says. The availability of such a product is relatively new, he adds. “It’s not the most exciting bit, but for us to be able to go specify things off-the-shelf that work with CLT just shows how the industry has matured.”
Other details had to be developed in-house. Worried that the weight of the brick, accruing over the building height, would gradually crush the CLT floors, the design team worked with Binderholz to cut pockets into the edge of each CLT floor deck. The pockets were then filled with structural grout, into which the wall panels that sandwich each floor panel would nest, transferring the vertical load from the upper wall panel to the one below.
One of CLT’s biggest advantages is the speed with which it can be erected: Dalston Works was built in 18 months, opening in summer 2017. Timber construction also makes for a quieter, less busy project site, Lomax says. On-site deliveries were reduced by almost 80 percent from a conventional site, and Lomax estimates that Dalston Works uses 25 percent less CLT per square foot than Murray Grove due to an increased understanding of and trust in the engineered wood product.
If building with CLT has a downside, it’s the amount of upfront design work required. To prefabricate Dalston Works, every cut, every groove, every hole needed to be executed accurately. More often than not, the finesse is there though sometimes the project team has to be convinced, Lomax says. At Dalston Works, floor openings for plumbing were sized nearly 8 inches at the request of Regal Homes to account for any potential misalignment. “Funny enough, our pipe went in a dead-straight line and then we had these huge holes in the wood that we had to try to seal up,” Lomax says. “It actually became a big task.”
Despite not blatantly announcing itself as a wood building—or perhaps precisely because it doesn’t—Dalston Works represents another step on the evolutionary path of tall timber construction. It’s an evolution with significant implications for the world’s cities, not least because of CLT’s promise in supplying urban housing. “It’s important to us to demonstrate that all developers of large-scale housing should be considering timber,” Lomax says, “because there is absolutely no reason not to.”
