Tallhouse is a New Urban Housing Model for 21st Century Cities

Building professionals have struggled for years with the fact that building housing takes too long, costs too much money, and uses too much energy, both operating and embodied. Today we have a housing crisis, a carbon crisis, and a health crisis, yet the building industry has barely changed. It seems that every building is a one-off with a different team starting from scratch.

Tallhouse aims to change all that; it is described as a "new urban housing model for 21st-century cities." It is not prefab as much as predesigned by a team led by John Klein of Generate. The firm writes that "Tallhouse, a catalog of systems, is intended to accelerate and de-risk the adoption of easily digitized and sustainable materials," addressing some of the fundamental problems of building design and construction:

"Current design processes lack the pre-rationalization of manufacturing and assembly, leading to a pressing housing affordability crisis, and to the non-usability of innovative materials in actual constructions. The Tallhouse, comprising a catalog of four mass timber structural solutions, illustrates a range of mass timber design options, all digitally engineered to address the need to build more quickly, sustainably and cost-effectively."

A benefit of designing a catalog of systems instead of a one-off building is that you can put together a terrific team. John Klein certainly has done that, and set up a conference for Treehugger to meet a few of them: Julie Janiski and Aurora Jensen of Buro Happold, doing the structural engineering and the embodied carbon analysis, and Nicole St. Clair Knobloch of Olifant Ecological Market Development, consulting on carbon and forestry.

Ever since cross-laminated timber (CLT) first hit the scene with the Waugh Thistleton timber tower in London in 2007, it has been seen as a faster, simpler way to build. John Klein told Treehugger that it created "a potential for mid-rise, high-density housing and commercial urban development, and thinking about it as a replicable system rather than a one-off."

Since then, the importance of eliminating the embodied carbon of concrete and steel has made it the best choice for low-carbon mid-rise buildings, but there are still, as John Klein described them, "challenges, problems, and misconceptions." For example, we show a lot of all-wood buildings, but Klein notes:

If you look at the embodied carbon chart, you see that steel beams and columns are quite carbon friendly. It's the concrete in the floors and cores that are carbon-intensive. We see an incredible value in a hybrid steel-timber building, and having the steel and timber industries unit in these high-density systems.

I used the opportunity to ask Nicole St. Clair Knobloch some of the questions that readers often ask me, such as: Does using CLT in low buildings make sense compared to stick framing? She tells Treehugger that the intent is not to compete with stick framing on low buildings, but with steel and concrete on midrise. Then, about the use of wood in general and the state of the forests. She tells Treehugger:

"So many of our forests are growing far more than we are harvesting, or could even imagine harvesting. We are bringing value to the forests, which keeps them from being lost to development. Also, we are losing trees standing in the forest which are eventually dying because of climate change and just age, and when we lose trees in the forest, the carbon is lost straight to the atmosphere. When we harvest trees in a long-lived product you are taking the carbon out of the forest and storing it in the building, and you then you grow more trees. It is a giant carbon pump. So you are drawing carbon down out of the atmosphere, you are moving it into a long-lived product, and you are offsetting the use of very climate-damaging materials."

Another point that is often made is that so much of the tree, from the leaves to the roots, is left to rot, and only about half of the tree (and its carbon) is actually used.

"There are two ways to look at that issue. It's true that the 'throughput' of a log, the amount that is turned into lamstock, (wood good enough to laminate) is less than 50% maybe only 30%, but the forestry industry is using much of the rest of the log for other products; now there is a real movement to turn it into insulation, they don't leave valuable stuff around. But another point is that if it wasn't harvested, the tree would be rotting and releasing its carbon anyway."

A concern was raised by architect Michael Eliason about flanking noise transmission around the ends of CLT panels; John Klein noted that this can be a problem but they have acoustic consultants, sound-absorbing mats, and gypcrete topping to exceed the code requirement. "It is an issue in timber buildings, and design teams have to be considerate of it."

A CLT slab is not cheaper than a concrete slab, but it gets installed much more quickly and time is money. Savings really start to accrue when you combine it with other systems. From the Tallhouse brief:

"To reduce costs, these structural bays are driven by the use of 5-ply cross-laminated timber in the floor systems, additionally offering a reduced construction schedule from rapid assembly. To maximize savings, the four systems were approached from an integrated design standpoint, with a prefabricated panelized exterior wall system, modular bathroom and modular kitchens, and prefabricated mechanical, electrical and plumbing assemblies."

The images are all of one particular building, the first Tallhouse, but the big idea here is that it is again, not a building but a catalog of existing proven components:

"The Tallhouse is a catalog of pre-engineered systems, customizable to the needs of a wide range of projects. Generate partners with architects and developers to digitally integrate these systems into their residential and commercial projects. Working with pre-vetted, replicable systems, enables significant acceleration in project delivery, while permitting architects to spend more time on the creative process of design, resulting in the delivery of at once higher-quality and cost-effective projects."

There is much that is groundbreaking here. Figuring out how everything goes together with a new material like CLT is hard and time-consuming for architects, and prices from contractors come in high because they have not dealt with it before. Architects have always picked parts out of catalogs, so it is not a stretch to look at this as a wonderful new tool for making selections that are tested and proven by consultants with worldwide experience, like Arup and Buro Happold.

The promise of prefabrication was not just that it was built in a factory, but that it was built better, and that there is enough repetition that practice makes perfect. What Generate has done here is a mix of predesign and prefabrication, all selected to minimize the operating and embodied carbon footprint. It "aims to revolutionize the construction industry by bringing down CO2 emissions while streamlining the construction of cost-effective, urban housing." But they may also revolutionize the profession of architecture in the process.