The Cornish-Windsor Bridge crosses the Connecticut River between the east end of Bridge Street, Windsor, Vermont and N.H. 12-A, Cornish, New Hampshire. As the Connecticut River forms the boundary between New Hampshire and Vermont, the low water mark on the west (Vermont) side, the bridge is being nominated concurrently by both states.
The bridge consists of two spans supported by two flanking timber lattice trusses adapted from the Town patent design. The trusses are built of six-by-eight inch spruce timbers which are bolted together at intervals of four feet into the diagonal Town lattice pattern. Each truss has two upper and two lower multi-segmented chords bolted to the lattice members. Some joints in the chords have been reinforced with steel plates. Iron rods extend from the tops of the trusses to the abutments and pier to anchor tile bridge.
Two sets of upper lateral bracing extend between the trusses. One set forms crosses within the top beams; the other set connects the top chords, with iron reinforcing rods extending through the apexes formed by adjoining crosses. Wood struts provide additional reinforcement between the upper intermediate chords and the top beams. The lower lateral bracing forms crosses between the bottom chords, with iron reinforcing rods extending through the apexes of adjoining crosses.
The massive west abutment and central pier of the bridge are built of stone blocks mortared together. The east abutment is completely faced with concrete. The west abutment has some concrete facing on the north side at water level. The extreme ends of the trusses rest on secondary abutments which are recessed behind the primary abutments and built of irregular stone slabs laid dry. Wing walls also built of stone blocks extend upstream from both abutments. The central pier is rounded on the north (upstream) side and flares outward toward the river bed to deflect floating debris and ice.
The bridge is 450.5 feet long at floor level. The gable ends overhang the roadway six feet at the east portal and eight feet at the west portal. Hence along the ridge the bridge is about 465 feet long. The pier stands nearly under the midpoint of the bridge: the two clear spans measure 204.6 feet and 203.7 feet respectively east and west. The wood floor begins 1.5 feet inside the east portal and 3.5 feet inside the west portal; the approaches are paved. The floor (and road surface) consists of planks laid flat and parallel to the trusses. The overall width of the bridge is 23.5 feet. The roadway is 19.5 feet wide, which allows two-way vehicular traffic through the bridge. The posted legal load limit is six tons.
On the exterior, the trusses (and sidewalls) of the bridge are sheathed with matched are hung vertically and painted grey. Eighteen small square windows with hoods are cut at regular intervals in each side wall of the bridge. The windows in one wall are spaced diagonally opposite those in the other wall. Vertical matched boards, which are painted white for increased visibility, protect the ends of the trusses immediately inside the portals. The gable ends, which are also painted white, are sheathed with horizontal clapboards. The portal openings are framed with semi-elliptical arches.
A medium-pitch gable roof covers the entire bridge; it does not overhang the gable ends. The roof is framed with light rafters, which extend from the top chords to abut at the ridge. There is no internal bracing connected to the roof structure. The roof is covered with corrugated metal sheeting.
The Cornish-Windsor Bridge has the numbers (New Hampshire) 29-10-09 and (Vermont) 45-14-14 in the World Guide to Covered Bridges published by the National Society for the Preservation of Covered Bridges. The number assigned to the bridge by the New Hampshire Department of Public Works and Highways is 064-108; the number assigned by the New Hampshire Department of Resources and Economic Development is 20.
The original physical appearance of the bridge is known to have differed somewhat from its present appearance. The roof was covered originally with wood shingles, which were replaced with the metal sheeting in 1924. The matched boards applied to the bridge and painted in 1954-55 probably replaced flush plain boards which were likely to have been left unpainted. The east abutment was built originally of irregular stone blocks; it was faced with concrete in 1921 after it had begun to settle.