A post-fi re rehabilitation included installation of a new metal roof on Bath-Haverhill Bridge. The New Hampshire bridge is the oldest authenticated surviving covered bridge in the U.S.
In the early 19th century, the U.S. was growing and rivers were a major obstacle to communication and land transportation. Bridges were needed for commerce, but deep water and spring floods made low, pile supported bridges impractical.
Bath-Haverhill Bridge, N.H.
At that time, wagons were stored away in winter and replaced by sleighs. Road-clearing vehicles that looked like oversized barrels were used to roll the snow fl at and hard. Th is caused a problem for wooden bridges that couldn’t support the packeddown weight of a long winter’s snow. Because of the beauty and historical mystique of the covered bridge, it’s easy to forget the practical reason 19th-century builders walled-up the sides and placed roofs over their bridges; they wanted to protect the bridges from the elements. Covered-bridge building was as much art as science. Builders were skilled craft smen with little formal education, oft en drawing on their experience in building barns.
North Hartland Covered Bridge
They knew the characteristics of the materials they worked with, including the load-bearing strength. Because a wooden-truss bridge’s strength comes from being under constant compression, every timber and joint in the frame must fi t precisely to distribute the load evenly. A typical 100-foot (30-m) lattice-type bridge could have almost 1,000 handcut, hand-pegged joints. Th e fact that wooden-covered bridges built more than a century ago still are in service is a tribute to the craft smanship with which they were built.
RESTORING A CLASSIC
The Bath-Haverhill Bridge in New Hampshire is the oldest authenticated surviving covered bridge in the U.S. Built in 1829, the bridge is 256-feet (78-m) long and has two spans of 104 and 121 feet (32 and 37 m). It has an overall width of 27 feet (8 m), a roadway width of 14 feet (4 m) and a maximum vertical clearance of 11 feet (3 m). There is a sidewalk on the north side of the structure. Th e bridge is posted for three tons (2.7 metric tons) and is limited to passenger cars only. In 1983, a fire damaged approximately 190 feet (58 m) of waterline housing on the bridge’s sidewalk.
Pittsfield Bridge, Pittsfield, Vt.
The damage to the structural portions of the bridge was very minor and included heavy soot on several members, as well as a slight charring of a few lattice members. The post-fire rehabilitation included replacement and repair of the deteriorated and damaged members, abutment and pier repairs, and a new metal roof. Metal was chosen for its durability and its snow-shedding capabilities. JEI Iron Horse Standing Seam Roofing, Tunbridge, Vt., installed the new roof and included 8,700 square feet (808 m2) of 24-gauge, charcoal-gray standing-seam roof panels. Wright Construction Co., Mt. Holly, Vt., supervised the restoration and constructed scaff olding on either side of the bridge, allowing JEI to rollform the metal on-site and install it from both sides of the river.
WHAT’S OLD IS NEW
Mill Bridge, Plainfield, N.H.
Not all covered bridges are a century old. In fact, the North Hartland Covered Bridge, North Hartland, Vt., was completed in October 2001. The bridge, constructed by Greensboro Bend, Vt.-based Restoration and Traditional Building Co., was assembled at a nearby recreation fi eld and moved to its place on the causeway of the North Hartland Dam. Twin covered bridges had served the causeway, crossing the Ottauquechee River at the North Hartland Dam, until the Great New England Hurricane of 1938 took out one of the bridges.
According to Jan Lewandowski, owner of Restoration and Traditional Building, the wiped-out span was replaced with a steel and concrete structure. It later failed, but the remaining covered bridge remained in great shape. Th e town decided to replace the failed span with a new covered wooden bridge. The two covered bridges are referred to asthe North Hartland twin bridges. Th e new bridge is similar in construction to the other covered bridge, which was built in 1919. Th e new standing-seam roof installed by JEI is 3,000 square feet (280 m2) of thinner, 26-gauge, mill-fi nish Galvalume, rollformed on-site. Like the Bath Haverhill span, the North Hartland Bridge is for passenger-car traffic only.
Fisher Concord Railroad Bridge, Wolcott, Vt.
Although many of New England’s covered bridges allow only passenger vehicles, some originally were designed as railroad bridges and still serve rail uses. Th e Fisher Concord Railroad Bridge, Wolcott, Vt., was built in 1908 and carried the engines and trains of the Boston & Maine Railroad. The live load of the Fisher Bridge, built of wood, was capable of handling up to 375,000 pounds (170100 kg) of train.
This bridge has a full-length cupola, which allowed the smoke from the steam locomotives to vent through the bridge’s roof. Nonetheless, water infi ltration, as well as ash and sparks from steam trains, damaged the roof and roadway. Seven years ago, Lewandowski worked with JEI to install a new roof, replacing an asphalt version and the cupola with 3,200 square feet (297 m2) of 24-gauge Galvalume. A steel pier was built in the river and now supports four steel girders that carry the railroad live load. Th e bridge is 109-feet (33-m) long and spans 103 feet (31 m) of water. Its width is 15 feet (4.5 m), and it has a single railroad track.
JEI also replaced the roof on the Mill Bridge—a railroad span also known as the Meriden Bridge—in Plainfield, N.H. Built in 1880, the bridge is 80-feet (24-m) long with clear spans of 37 and 29 feet (11 and 9 m). It has an overall width of 17 feet (5 m) with a roadway width of 13 feet (4 m) and a maximum vertical clearance of 13 feet (4 m). Th e bridge is posted for six tons (5.4 metric tons). Th e original roof of the building was composed of shake shingles but a new 2,200-squarefoot (204-m2) forest-green, standing-seam roof was chosen for its durability and because metal is a historically acceptable substitute for shakes in bridge restorations.
Some covered bridges can be found on private land. Joe DeSena is managing director of equity trading at New York-based Col-lins-Stewart, an independent investment bank. In 2005, he bought several acres in Pittsfi eld, Vt., with the intent of restoring a covered bridge on the property. Th e 55-foot- (17-m-) long Pittsfi eld Bridge at one time had a corrugated metal roof and before that was covered in cedar shakes. JEI again did the new roofi ng, putting up 26-gauge Galvalume to replace an old corrugated roof with a new standing-seam roof that DeSena, a private owner already noted for other local building restorations, chose with the intent of saving and preserving a local area landmark.
METAL ON TOP
Most covered bridges that undergo restoration are candidates for a variety of roofi ng materials. During the past decade, metal has emerged as a preferred choice. Robert H. Durfee is a licensed engineer with 30 years’ professional experience in transportation and structural engineering. He also is a nationally recognized expert on covered bridges and a noted author of technical papers, publications and presentations about bridge and structural engineering. Having considered a number of diff erent roofi ng materials, including cedar shakes, asphalt and metal, he believes standing seam is the best solution.
“Cedar shakes are a historically accurate roof system for existing and new covered bridges,” Durfee recently told members of a covered-bridge preservation organization. He further notes, however, that it is one of the most expensive systems and poses a number of maintenance issues. “The shakes are subject to drying, warping, splitting and eventual leaking, and tend to collect mold and fungus in shady areas. A cedar-shake roof will last about 20 to 25 years,” he says. Asphalt shingles, Durfee observes, are less expensive and easier to install than cedar shakes. But like cedar shakes, they are prone to collect mold and fungus in shady areas. “Asphalt shingles last about 20 to 30 years before wearing out and needing replacement,” Durfee says. “Th ey need to be installed over a substrate [such as plywood sheathing or solid boarding], which adds a lot of dead-load weight to the bridge. When replacing an asphalt roof, disposal of the old asphalt shingles can be problematic and expensive; they are considered hazardous-waste material, requiring special disposal methods.
This adds to the cost of roof replacement.” Metal roofs, he notes, are the least expensive of the three roofi ng materials. “Metal roofi ng was fi rst manufactured and became available in the 1890s as corrugated metal sheeting,” Durfee points out. “It was used on barns, homes and probably new coveredbridge construction at the time.” Durfee emphasizes the longevity of a metal roof on preservation projects. “Metal roofs can last 50 years or more,” he says. “Many covered bridges that had shake roofs were replaced with metal roofs beginning in the 1890s up to the present day. Th ese older applications of metal roofs have achieved some historical signifi cance. Several state historical-preservation offices recognize and approve of a metal roof as a historically accurate and acceptable roof system for a covered bridge.”
Philip Pierce is a professional engineer in Treadwell, N.Y. He established a consulting practice in 1999 with primary focus on covered- bridge engineering. His recent assignments include work on six covered bridges. He echoes Durfee’s sentiments and adds another thought about standing-seam roofs. “Wood shingles were the available material at the time of initial construction of historic covered bridges. Hence, according to the degree of concern for that historic precedent, replacement shingles over the years oft en were wood shingles. In my experience, the installation of wood shingles may still lead to leaks in the roof, regardless of the degree of care with the installation, and they are prone to breakage. Needless to say, a leaking roof is the bane of covered bridges.” Pierce suggests standing seam as the logical alternative.
“The use of metal roofi ng has provided a great improvement in the ability of the roof to shed heavy snow loading. Such loading can be deadly to covered bridges—so much so that some covered-bridge owners have regularly shoveled snow off the roof of a covered bridge. I am a strong advocate of using metal in areas where snow load can be signifi cant,” he says. “In my experience, historic- preservation interests oft en accept the use of metal as a prudent means of prolonging the life of covered bridges and recognize the prominence and long-time use.” Like many engineers, these New Englanders are hopeful that standing-seam roofs will bring another 50 years or more of life and protection for a signifi cant part of our country’s history, culture and development.
Kevin Corcoran is vice president of sales at Englert Inc., Perth Amboy, N.J. Corcoran is a 29-year veteran of the metal roofing industry. He can be reached at k.corcoran@englertinc. com.
PANEL DISCUSSION
The roof panels used in the covered-bridge projects discussed in this article are from the A 1300 roofi ng panel series from Englert Inc., Perth Amboy, N.J., www. englertinc.com.
The narrow-seam panels feature a mechanical seam and are UL-90 tested. They have been ASTM water- and air-infi ltration tested, as well as tested under ASTM E-1592, “Standard Test Method for Structural Performance of Sheet Metal Roof and Siding Systems by Uniform Static Air Pressure Difference.”
The profi le is compliant to Energy Star and LEED standards for energy savings, recyclability and reuse. The panels carry a weathertightness warranty, as well as a 35-year finish warranty.