Small CLT is Beautiful: A different model for mass timber

Timber Age goes to the forest and harvests trees that might otherwise burn.

Timber Age Cross Laminated Timber

The session at the Passive House Network conference in Denver was titled “Passive House, Embodied Carbon & Environmental Sustainability,” all my favourite buzzwords, and included personal hero Chris Magwood of RMI, so of course I had to go. I didn’t pay much attention to the other panellists, Kyle Hanson and Christopher Hamm of Timber Age Systems; a quick look at their website indicated that it made modular homes out of cross-laminated timber, which I have thought was one of the dumbest ideas in the construction industry.

Kyle Hanson, Chistopher Hamm, Chris Magwood, Moderator Lindsey Love

I had my questions for them prepared in advance:

1. Why would you use CLT for low-rise construction when it uses 4.8 times as much wood fibre as a frame wall?

2. Why would you build modular out of CLT and use even more wood with the doubling up of walls and floors, be limited in your designs, and ship air instead of panels?

But it turns out that I had much to learn on both counts. While the modular industry (and I) consider modules to be boxes, Timber Age provides “panelized modular buildings,” which can be flat-packed. They call themselves “a modular home builder” but are providing a panel system, not a complete building.

And what an interesting panel system it is. It turns out that using 4.8 times as much wood is a feature, not a bug. All over the western United States, there are “hot spots” where forests of second-growth Ponderosa Pine need thinning to prevent them from going up in flames. In this case, the more wood used, the merrier.

Conventional CLT plants make giant panels with lamstock (laminating stock) made from graded dimension lumber (usually 2x6) squeezed in huge, expensive presses. Katerra spent $150 million building its ill-fated CLT plant in Spokane. Timber Age will set up 5,000-square-foot flying factories at about $2 million a pop to make “small” CLT.

photo Timber Age

Timber Age goes to where the pine is with its own sawmill, and cuts up thinner lamstock at 5/4 inches thick. (that’s why the Ponderosa Pines are still standing- they are too small to make regular dimension lumber efficiently)

Spreading the glue/ Timber Age

Timber Age lays it up in smaller panels, so it doesn’t need the expensive finger-jointing machine required to make longer lamstock. They spread the glue by hand and then use a homemade vacuum press, where you suck out the air and let the atmosphere, at 8.5 tonnes per square meter, do the work.

So, the panel isn’t as big or strong or thick as a conventional CLT panel and doesn’t yet meet standards like PRG 320. Who cares? They are not building timber towers, and the panels are more than strong enough for one and two-storey buildings.

Timber Age

They take their home-baked CLT and add a breathable air barrier (Wrapshield IT- I have this on my own home; see Help, my house is covered in sticky orange frogs). I-joists are added to provide a space for insulation (and stiffen the wall even further) Add some battens to hold the future exterior siding, fill with cellulose insulation. and more Wrapshield to hold it all together. Truck them to the site, tilt them up, drop the roof on, and voila: a building that should hit the Passive House standard.

Interior of Accessory Dwelling Unit

Even Chris Magwood, a notable skeptic about CLT, is impressed with the way they are using wood that would otherwise likely burn, and turning mass timber into a local business with limited transport distances. It’s an instant wall that doesn’t need drywall or other finishes and looks and smells great.

There were some lessons learned here. My mantra, learned from engineer Will Arnold, is always “use less stuff,” but these guys show that it isn’t always true, and my preconceived notions are not always right. And as E. F. Schumacher noted, small is beautiful.