Public House have been experimenting with timber truss designs for a number of years now. They're a very engineering way to span long distances or support heavy loads. By taking a typical beam, distributing the area away from each other with connecting diagonal members, the structural capacity of the same amount of material increases exponentially. Almost all lightweight, long-span structures you see are trusses - bridges, stadiums, concert halls.
For obvious reasons, they're also difficult to introduce into our (slightly smaller) projects: trusses require depth in order to function; the triangles and diagonals that make up the truss are often tricky to accommodate into architecture; and they need to be assembled from lots of individual elements.
But often, trusses could make a big difference when we're asked to span long distances or transfer heavy building loads over a new open space below. Normally, we use a heavy steel beam or a glulam timber beam to carry the heavy load within an efficient structural depth, to maximise ceiling height. The drawback of this approach is the weight of the structural beam and associated material and manufacturing cost. Since deep down we are engineers, we've always been chewing on ways to replace these heavy, expensive and highly engineered solutions with something more simple and cheap.
So we started investigating how to design truss systems that could be constructed from basic raw timber sections and assembled using simple connections that kept the overall cost below that of an equivalent steel or glulam beam.
For long spans where a heavy steel beam or engineered glulam beam is required, using a truss dramatically reduces the material quantities required. So much less, that where we've developed a truss solution, we've been able to reduce material weight by 50% (vs. steel or glulam) and use only basic small raw timber sections, the ones you can buy from your local timber merchant.
But the truss connections were the key to making this idea viable. Limiting ourselves to cheap and readily available standard timber sections, it was important that the connections and the carpentry to fabricate the truss were also simple (heavy steel/glulam beams still benefit from how quickly they can be brought from the supplier and installed on site).
With small truss members, the connections at the nodes between the elements can require a lot of bolts spread along the member length. Typically, custom bolted steel plates or shoes are used. We developed a cheap and simple bolted plywood plate connection alternative: a full-timber solution, easy to fabricate using standard CNC machines, and the whole thing can be assembled in the workshop or on site.
On projects we've worked on, this system is a viable alternative to heavy steel beams and engineered glulam beams. The cost is around 50% lower, the weight is around 50% lower, its easy to assemble and lift into place.
The embodied carbon is also 80% lower than the steel beam and 50% lower than the glulam equivalent. As with all the design work that Public House does, it follows a careful logic around sustainability: Do less and retain more; Use fewer materials by thinking more and making them work harder; try to re-use materials, or standard section sizes that can be re-used; and use materials that are not so energy-intensive. The truss follows this logic - where the structure is required, we've developed an innovative system that uses simple and standard-sized materials that work hard. The embodied carbon calculations are reflective of this approach.
Kala Festival - Unit 38 / Public House
Self-build project - Public House
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