A walk during the pandemic
12 May 2020
Image Credit: Bill Birdsell
Architectural Credit: Timber Framers Guild
My design work has slowed but fortunately not stopped. I’ve adapted to zoom and other tools but to keep my sanity and stay active I walk. It is one of the few things that is still safe to do and it uses up this idle time. Guelph is gifted with many trails and open spaces, without people, to explore on a cold day in the sun. One of my haunts, not far from where I live features the Guelph Bridge.
There is a long history of covered bridges in North America dating from the 19th century to current times. Wood was available and labour aplenty. It made sense to bring these two resources together to span small and mighty rivers. Like all wood structures, if you can manage the elements, particularly rain, they will last an extremely long time. By integrating an iron tension rod, the “Howe Truss” invented in 1840, solved the problem of longer spans. New Brunswick was home to the longest such bridge in the world with six spans combined to extend over 1,282 feet. Fortunately over fifty covered bridges remain in the province today.
The kissing bridges as they are often known are a pillar of New Brunswick tourism. Closer to my home there is a historic covered bridge near Kitchener-Waterloo. The West Montrose Bridge is the oldest in Canada dating from 1880. The bright red paint that covers the cladding, besides the span of 198 feet, adds to the visual impact it has on the built environment of the region. A designation by Ontario’s Archeological and Historic Sites Board adds to its tourism draw. Guelph discovered this additional attribute when it installed its covered pedestrian bridge in 1992. Guelph received the gift of this instant landmark when it was chosen as the site for a Timber Framers Guild conference. What better thing to do when you bring 400 timber framers together than to build a bridge spanning 132 feet in five days.
The conference organizers chose a pair of giant “town lattice trusses” as the primary structure. That truss is one of the quicker ones to fabricate. This also enabled each attendant to the conference to sign and drive a peg into one of the joints of the lumber forming a truss. The bridge contains over 50,000 board feet of lumber, approximately 30,000 in the trusses alone or enough for four or five houses. The trusses are constructed of Douglas Fir, except for two pieces of willow used as large posts. The willow was from a tree cut down and milled to make way for one of the bridge abutments. The posts stand in small part as a recognition that these behemoths were traditionally built from local trees. Now we earn environmental benefits from sourcing materials for our projects close to home.
Timber framing is a distinctive style of building construction in which heavy timbers frame the structure instead of the use of more slender dimensional lumber. One of the most defining elements of timber frame is its unique joinery. Like furniture, heavy timber is joined together via mortises and tenons, then secured by wooden pegs. Approximately forty years ago craftsman revived the timber framing tradition and ushered the design style into the modern vocabulary. Similar to 1840, hybrids have now formed and the inconvenient stresses on connections are now solved by steel concealed within the joint.
Unlike much of current construction, there is an opportunity for a social aspect to timber framing. All of the structural timbers of a building are prepared ahead of time. Then a community can come together to fit the pieces together and hand raise the structure using historically authentic frames, pike poles, ropes and people power. The construction of the Guelph Bridge required over 21,000 hours of labour and after it was done, I can attest that the celebration was worth being at.
Bill Birdsell, OAA, FRAIC, Architect, Guelph
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