Wetland Trail Design and Construction: 2007 Edition
Finishing Details, Cont.
Pedestrian Railing Types
Safety must be the first consideration in selecting a railing system. Safety requirements are primarily determined by the relative accessibility of the trail. Railing types must fit the appropriate Recreational Opportunity Spectrum class. Railings are of three basic types:
Railings attached to buildings (visitor centers, for example), must meet building code requirements such as those listed in the International Building Code (IBC). This code requires a railing at least 42 inches high that a 4-inch sphere will not pass through.
Handrails on bridges need to meet the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges. Although most of the structures described in this book are not bridges, we offer these specifications for information. AASHTO requires 42-inch-high guardrails on all pedestrian highway bridges. Bridges on fully accessible trails usually need this type of railing. This code requires handrail at least 42 inches high for pedestrian traffic and at least 54 inches high for bicycle or equestrian traffic. A 6-inch sphere must not pass through the railing in the bottom 27 inches, and an 8-inch sphere must not pass through the area above 27 inches.
Handrails for more remote trail bridges must be at least 42 inches high for pedestrian traffic and at least 54 inches high for bicycle or equestrian traffic. These handrail systems must also have at least one intermediate rail so that vertical distances between rails do not exceed 15 inches. Three-fourths of all Forest Service trail bridges fall in this category.
Not all wetland trail structures need railings. If the trail itself has more hazardous drops than the trail bridge would have without a handrail, a handrail is probably not required. Other considerations, such as convenience, may justify installing a handrail. Although IBC requirements and AASHTO specifications do not govern trail construction, they can serve as guidelines. As a general rule, any fully accessible trail with a drop of 3 feet or more, or a more remote trail with a drop of 8 feet or more, should have a pedestrian railing system. All accessible trails require a curb. A wheelchair handrail is required for any accessible trail bridge on a grade of 5 percent or steeper. Document your decisions with a design warrant retained in your files.
Railing Installation
Install the railings after the posts and deck are complete. Most railings consist of a top and bottom rail, usually 2 by 6s, although 3 by 6s make a better splice and a stronger rail. The stronger rail permits posts to be spaced more widely than if 2 by 6s were used for rails. The rail can also be cut and drilled in a shop where the splices can be cut accurately and more efficiently.
Often there is no clear direction regarding splicing the railings if the span exceeds 16 feet, the longest lumber that is readily available. It is difficult to butt splice a railing to the surface of a post that is less than 6 inches wide without an awkward splice or a maintenance problem (figure 61).
Walking on the top rail is a potential problem. Round logs or poles have been used to discourage visitors from walking on them, as well as 4 by 4s and 6 by 6s laid diagonally with one corner up. Another technique is to cut the tops of all posts at an angle and place a 2 by 6, or 2 by 8, on the cut surface. This helps to shed water and prevent decay.
Figure 61--Four methods of splicing rails. It is best to cut the rails in
the shop. Use carriage bolts with the round end on the inside of the
railing to prevent users from snagging themselves.
The edges of all rails should be "edges eased." Edges eased is a trade term indicating that the corners along the edges of the piece of wood are rounded. To reduce splinters, the radius of the handrail edge should be ½ inch or more.
Installing a handrail on a curved bog bridge or angled boardwalk can be a challenge. One way to do this is to use steel angles. Measure the distance between posts and cut the rail to that length. Nail or screw the angles at the ends and to the outside of a 2- by 4-inch or 2- by 6-inch rail. The angles will have to be bent slightly to conform to the different alignment of the posts. Hold the rail in place and nail or screw the angle to the side of the post with the inside face of the board flush with the inside face of the post. Measure the distance between the centerline of the two posts and cut a 2 by 6 to that length. Round the ends slightly and bolt the 2 by 6 to the 2 by 4. The result will be a stronger rail than a single piece of material. This technique may also be used for straight sections of railing to avoid nailing or screwing into the face of the post (figure 62).
Figure 62--One method of installing rails on curving
boardwalks using steel angles bent to accommodate
the curvature of the structure.
For rails on curved trails, short wedge-shaped pieces of lumber can be used as shims between the posts and the rails. The wedges should be oak or cedar. Wedges are difficult to cut in the field. You could notch posts to the correct angle to accept the rails, but this is also difficult.
Cable or wire rope can be used as a railing system in some specialized applications (figure 63). Often the posts are close, 4 to 6 feet, and the cable is strung through holes drilled in the posts or through screw eyes. A single piece of cable may be strung through all the holes in the upper part of the posts, down the last post to the next lower hole and continuing this process back to the beginning through the lower holes, reducing the need for many splices. Use cable tensioners as needed.
Figure 63--Wire rope is used here as part
of the railing system.
Curbs (Bull Rails)
Curb and bull rail are two names for the same thing. If the drop from a boardwalk is about 36 inches or less, a curb is usually installed. A curb is required for accessible trails. Curbs help to delineate the trail tread (figure 64).
Figure 64--Typically, curbs (bull rails) are used when the deck is no
more than 36 inches off the ground.
Curbs placed directly on the surface of a wood deck can cause the deck planking to decay. Leaves, needles, and dirt accumulate against the curb, absorb water, and cause additional decay. During the winter, ice and snow will build up on the deck, causing a hazardous condition.
To keep the deck from decaying, place the curbs on blocks. A finished block of 2 by 4 lumber is only 1½ inches thick. Leaves and dirt can still build up against the curb and under it. With just 1½ inches of space between the curb and the deck, it is difficult to get a shovel under the curb, making this area almost impossible to clean. A better solution is to use two blocks of 2 by 4 lumber, one on top of the other, or one block of 4 by 4 lumber (figure 65) to eliminate the opening under the curb. Litter will not be trapped, and melting ice and snow will run off more quickly. These openings underneath the curbs sometimes are called scuppers, an old nautical term.
Figure 65--Having at least 4 inches of
clearance under the curb is best.
Bulkheads (Backwalls, End Dams, Faceplates)
Bulkheads must be installed where wood construction meets the earth trail at each end of a puncheon, bog bridge, or boardwalk. They function as retaining walls to support the earth. They also protect the end grain of the stringers from decay and insect damage (figure 66). Bulkheads should always be treated timber.
Install the top of the bulkhead level with the top of the stringers, covering the gap with a piece of deck plank. This is the best way to keep moisture away from the stringer.
Extend the backwall 1 to 2 feet on each side of the structure to keep wet soil away from the sides of the stringers.
Figure 66--Bulkheads serve as retaining walls to support the earth,
and they protect the stringers from decay and insect damage.
