The Town Lattice Covered Bridge

The Town Lattice Covered Bridge

Ithiel Town, an architect by education, obtained his first patent for a unique type of timber truss in 1820. All the other trusses principally rely on large and heavy timbers that require skilled artisans to properly craft the rather elaborate joinery between the various components. Town sought a means of constructing bridges that would rely on an easily adapted design and would require less skilled labor. His patented truss developed a configuration that could be extended to a wide range of span lengths with relatively little modification of the configuration. In the opinion of many informed bridge aficionados, his patented truss represents arguably the most important development in the history of covered bridges, and one that remains a popular and enduring style.

Town's lattice configuration relies on assembling relatively short and light planks that were available and easy to handle. He connected the overlapping intersection of members with round timber dowels or pegs, termed treenails, pronounced trunnels. The plank intersections in the web may have from one to three trunnels. Where chord members intersect with web or lattice members, the overlapping zone may contain as many as four trunnels. The dowels are often 38 to 51 millimeters (mm) (1.5 to 2 inches) in diameter. The parallel and closely spaced web members are joined to chords along both the top and bottom of the trusses. Two levels of chords commonly are used as the bottom chords. The top chords may have one or two levels of members. The lowest bottom chord provides the seat for the transverse floor beams.

Town, or lattice, trusses are most commonly comprised of thin members with pairs of chords on each side of the lattice webs. In this case, the truss is sometimes termed a plank lattice. The chord members generally are not spliced to abutting pieces at their ends, but the terminations are staggered so that any panel of chord has at least one unspliced member. A few Town lattice trusses were fabricated of heavier components using single chord members on each side of the lattice. In this case, the truss is termed a timber lattice. The chord members require splices at their ends.

The Town Lattice truss has been described as an uninterrupted series of crisscrossed diagonals forming overlapped triangles. These web members were fastened at their points of intersection so that independent action of any one triangle was impossible. This was the secret of the strength of the Town truss. Pine or spruce plank was the usual material used in the Town truss and holes were bored into the planks at every lattice intersection and at the places where the lattices were secured to the upper and lower chords. Wooden connecting pins called treenails or "trunnels" made of oak were soaked in oil and driven into these holes with a long-handled mallet called a Beetle (pronounced "biddle"). There were approximately 2,592 holes in a 100' lattice highway bridge requiring 912 trunnels to pin it together. These lattice trusses were laid out in a field adjacent to the bridge site and assembled and then the truss was jockeyed out over the river on falsework. The Town Lattice truss was very popular for both highway and railroad use. For railroad use, the lattice trusses were doubled for extra strength. This truss type was built in all the New England States, most of the Southern States and the Mid-West.

There remain about 135 bridges supported by Town lattice trusses. Town lattice trusses support varying span lengths, from relatively short (only 7.6 m (25 ft)), up to some of the longest covered bridge spans in the world. Individual Town lattice trusses span up to 49.4 m (162 ft). The oldest surviving Town lattice bridge (the Halpin Bridge in Middlebury, VT) was purportedly built about 1824. New examples of Town lattice covered bridges are still being built.

Alabama

Shushan Covered Bridge, Shushan New York

Kymulga Mill And Covered Bridge, Childersburg Alabama

Swann Covered Bridge, Cleveland Alabama

Clarkson Covered Bridge - Legg Bridge, Cullman Alabama

Nectar Covered Bridge, Nectar Alabama

Easley Covered Bridge, Oneonta Alabama

Horton Mill Covered Bridge, Oneonta Alabama

Bull's Bridge Covered Bridge, Kent Connecticut

West Cornwall Bridge, Cornwall Connecticut

Kilgore Mill Covered Bridge and Mill Site, Bethlehem Georgia

Cromer's Mill Covered Bridge, Carnesville Georgia

Pool's Mill Covered Bridge, Cumming Georgia

Steele's Covered Bridge, Dawsonville Georgia

Howard's Covered Bridge, Smithsonia Georgia

Auchumpkee Creek Covered Bridge - Hootenville Covered Bridge, Thomaston Georgia

Elder's Mill Covered Bridge and Elder Mill, Watkinsville Georgia

Red Oak Creek Covered Bridge, Woodbury Georgia

Imes Covered Bridge - Wilkins Mill Bridge, Saint Charles Iowa

Cedar Covered Bridge, Winterset, Madison County Iowa

Cutler-Donahoe Covered Bridge, Winterset, Madison County, Iowa

Hogback Covered Bridge, Winterset Iowa

Holliwell Covered Bridge, Winterset Iowa

McBride Covered Bridge, Winterset, Madison County Iowa

Roseman Covered Bridge - Oak Grove Bridge, Winterset Iowa

Ware-Hardwick Covered Bridge, Gilbertville Massachusetts

Old Covered Bridge - Upper Sheffield Covered Bridge, Sheffield Massachusetts

Fallasburg Covered Bridge, Vergennes Michigan

Skeen's Mill Covered Bridge, Flint Hill North Carolina

Bog Covered Bridge - Cilleyville Bridge, Andover New Hampshire

Keniston Bridge, Andover New Hampshire

Ashuelot Covered Bridge, Ashuelot New Hampshire

Wrights Covered Bridge, Claremont New Hampshire

Cornish-Windsor Covered Bridge, Cornish New Hampshire

Contoocook Covered Railroad Bridge, Hopkinton New Hampshire

Prentiss Covered Bridge - Drewsville Bridge, Langdon New Hampshire

Corbin Covered Bridge, Newport New Hampshire

Sawyers Crossing Covered Bridge, Swanzey New Hampshire

West Swanzey Covered Bridge, Swanzey New Hampshire

Waterloo Covered Bridge, Waterloo New Hampshire

Slate Covered Bridge, Westport New Hampshire

Coombs Covered Bridge, Winchester New Hampshire

Haverhill-Bath Covered Bridge, Woodsville New Hampshire

Beaverkill Covered Bridge, Beaverkill New York

Fitches Covered Bridge, East Delhi New York

Eagleville Covered Bridge, Eagleville New York

Grant Mills Covered Bridge, Hardenbergh New York

Lower Shavertown Covered Bridge, Methol New York

Newfield Covered Bridge, Newfield New York

Ashokan-Turnwood Covered Bridge, Olivebridge New York

Shushan Covered Bridge, Shushan New York

Mull Covered Bridge, East of Burgoon Ohio

Bartonsville Covered Bridge, Bartonsville Vermont

Hall Covered Bridge - Osgood Bridge, Bellows Falls Vermont

Bennington Falls Covered Bridge, Bennington Vermont

Henry Covered Bridge, Bennington Vermont

Silk Covered Bridge - Robinson Bridge, Bennington Vermont

Dean Covered Bridge, Brandon Vermont

Creamery Covered Bridge, Brattleboro Vermont

Kingsley Covered Bridge, East Clarendon Vermont

West Dummerston Covered Bridge, Dummerston Vermont

Hopkins Covered Bridge, Enosburg Vermont

Fairfax Covered Bridge, Fairfax Vermont

Green River Covered Bridge, Green River Village Vermont

Martin's Mill Covered Bridge, Hartland Vermont

Willard Covered Bridge, Hartland Vermont

Halpin Covered Bridge, Middlebury Vermont

Comstock Covered Bridge, Montgomery Vermont

Fuller Covered Bridge, Montgomery Vermont

Longley Covered Bridge, Montgomery Vermont

West Hill Covered Bridge, Montgomery Vermont

Hectorville Covered Bridge, Montgomery Center Vermont

Hutchins Covered Bridge, Montgomery Center Vermont

Williamsville Covered Bridge, Newfane Vermont

Brown Covered Bridge, North Clarendon Vermont

River Road Covered Bridge, North Troy Vermont

Northfield Falls Covered Bridge, Northfield Vermont

Upper Falls Covered Bridge, Perkinsville Vermont

Cooley Covered Bridge, Pittsford Vermont

Depot Covered Bridge, Pittsford Vermont

Hammond Covered Bridge, Pittsford Vermont

Gorham Covered Bridge, Proctor Vermont