A covered bridge is defined by its roof, but it is built around its truss. The truss is the frame that turns a pile of timber into a structure able to carry its own weight and a load across a gap. Three named systems account for most of the surviving Canadian examples: the Town lattice, the Howe truss and the Long truss. Each solves the same problem with a different arrangement of members.
The Town lattice
Patented by Ithiel Town in the 1820s, the lattice truss uses a dense web of crisscrossing planks pinned together at their intersections. Its appeal was practical: it could be built from light, sawn lumber and ordinary fasteners rather than heavy hewn timbers and complex joinery. A crew did not need master framing skills to assemble one.
- Light, interchangeable planks instead of large timbers.
- Loads spread across many small members rather than a few large ones.
- Forgiving to build, which suited rural crossings.
The Howe truss
The Howe truss, patented in the 1840s, combined timber diagonals with iron vertical rods. The iron members are in tension and can be tightened, which let builders adjust the frame as the wood moved. This hybrid of wood and metal made the Howe truss durable and maintainable, and it became one of the most common choices for covered bridges in eastern Canada — including the Hartland and Wakefield spans discussed elsewhere on this site.
In a Howe truss, the parts that pull (the verticals) are iron and adjustable, while the parts that push (the diagonals) are timber. That division let crews re-tension the bridge instead of rebuilding it.
The Long truss
Stephen Long's truss, from the 1830s, used timber for both diagonals and verticals, with paired counter-braced diagonals in each panel. It predates the Howe design and influenced it. Where the Howe truss reached for iron, the Long truss kept everything in wood, relying on the geometry of crossed braces to handle loads moving in either direction across the span.
| Town lattice | Crisscrossed planks, pinned; easy to build from light lumber. |
|---|---|
| Howe truss | Timber diagonals plus adjustable iron verticals; durable and maintainable. |
| Long truss | All-timber panels with counter-braced diagonals; an earlier wooden system. |
Reading a bridge from inside
Standing inside a covered bridge, you can often identify the system by looking at the walls. A dense diagonal mesh of planks points to a Town lattice. Heavy timber diagonals paired with slim metal rods point to a Howe truss. Crossed timber braces with no significant ironwork suggest a Long truss or a related all-timber design. The roof overhead is the same in each case; the frame behind the siding is what differs.
These systems were not unique to Canada — they spread across northeastern North America — but the surviving Canadian spans, from West Montrose in Ontario to the Quebec and New Brunswick crossings, keep these nineteenth-century engineering ideas standing and in view.