Boardwalk designs

Split timber

The boardwalk shown below, made in chestnut, lasted at least 10 years without major repair at Slapton Ley, South Devon, where it is used to cross an area of reedswamp. The split timber gives a rough, non-slip surface.

Half logs are not recommended for the decking as they need notching to sit steady, which entails a lot of work.

Railway sleepers

These have been extensively used in the past, but are now becoming very expensive in some parts of the country as supplies dwindle. Check local supplies before deciding on this method of construction.

This construction has been used at Risley Moss, Warrington. Whole sleepers were laid direct on the moss as stringers, with half sleepers used for the decking. Spacers of 10mm thick pieces of wood were used to make drainage gaps. Spacers were nailed to the side of the sleeper, and then each sleeper knocked tight against the previous one using a sledgehammer. The deck sleepers were not nailed to the stringers, as the weight is sufficient to hold them in place.

Finally, galvanised fencing wire was pulled taut along the decking and stapled to each sleeper, to discourage vandals from dislodging the decking.

Corners were turned in either of the two ways shown below.

Sleepers can be more economically used as longitudinal decking , but boardwalks of only two sleepers width are not recommended except for short obligatory sections. Longer sections inevitably develop paths alongside and look ugly in proportion, being much too narrow for the depth of timber. Three sleeper width boardwalks are sufficient for two-way traffic, and appear to ‘sit’ more attractively in the landscape.

Boardwalks made entirely of sleepers are relatively quick and simple to construct, provided that the sleepers do not have to be carried too far.

Sleeper and sawn timber

1. This takes longer to construct than the preceding design, but saves on sleepers and is less obtrusive in short vegetation. The stobs and cross-beams are 100mm x 100mm which minimises wastage. A boardwalk of this type has received moderate two-way use at Ben Lawers, Perthshire, for many years. The thick growth of vegetation at the side and under the edges of the boardwalk are testimony to its success.
   
2. The design below is suitable for softer ground. In very wet sections the sleeper bearers are turned to give extra height.
   
3. The following design has been in use for many years at Hothfield Bog, Kent, where the wet conditions and possible flooding require the boardwalk to be raised up to 500mm above the ground. The design incorporates a handrail on one side.
   
4. A very substantial boardwalk has been constructed at Castle Espie, a Wildfowl and Wetlands Trust reserve in County Down, Northern Ireland. The boardwalk links a series of small islands in a flooded former quarry on the shores of Strangford Lough. The boardwalk has telegraph pole stringers, resting on bearers of railway sleepers. The design includes handrails, and is similar in construction to the bridge superstructure shown here.

Sawn timber

The spacing of the decking and the dimensions of the timber give these boardwalks a ‘lighter ’ appearance in the landscape, than those involving the use of railway sleepers. They can be very durable if good quality, properly preserved timber is used, and the construction is sound and level. Designs which have two stobs supporting each stringer are easier to construct than those with three stobs for each stringer, as careful levelling is needed to spread the weight evenly between three stobs. Sections can either be joined, with stringers joining at a stob, or in independent sections. In general, joined sections with shorter stringers are stronger and easier to build than longer stringers in independent sections. Stringers over 2m in length need either three stobs, or a central stringer is needed to give extra rigidity.

Many designs have been used, some of which are given below.

Chesil Beach, Dorset

Several short boardwalks of this design are used to provide routes from carpark to beach across a stable, vegetated dune. This is a simple design, with no joints required to be cut on site. A possible weak point is that the weight is taken by the cross-beams which are nailed to the stobs, rather than by resting the stringers on the stobs, as in other designs below. In practice, this does not seem to be a problem and the boardwalks are wearing well. The cross-beams could be bolted to the stobs for extra strength.

River Avon, Salisbury

This design is used for a boardwalk on a popular route through water meadows beside the River Avon, in Salisbury, Wiltshire. The central stringer is necessary to compensate for the long spacing between stobs.

The procedure used was as follows:

1. Clear vegetation as necessary. Dig holes for stobs 200-250mm deep, and then mell stob in to the required depth. Use a cross-beam and level to check that the pair of stobs are level. Attach cross-beam. Dig next pair of holes 3m along path, levelling back to previous ones.
2. Attach stringers, angling nails for extra strength.
3. Nail on decking, leaving a 20mm gap. A template of the correct thickness is useful for spacing.
4. Staple on chicken wire, tucking the ends over neatly. Nail on the toe board, at every other decking board.

SNH design

This design is recommended by Scottish Natural Heritage (CCS, revised 1989). A wooden bracket is used to join stringer to stob. Larch is specified instead of pressure-treated timber on sites where leaching of preservative may cause damage to surrounding habitat .

Gateshead

This substantial boardwalk was built to provide access to a wetland site with ponds and reed beds. Round fencing posts, cut to 500mm lengths, were used for stobs. To get the levels accurate, the stobs were set in dug holes, rather than being melled into the ground. This was a slow process, but resulted in a strong, stable structure.

Boulder bearers

Instead of stobs, this boardwalk is supported by boulders. Cross-beams are necessary to give the structure rigidity. The frame of stringers and cross-beams can be quickly constructed on a jig.

Sommerfeld Flexboard

This is a wooden and steel trackway designed for temporary roadways, which has been successfully used for footpaths in the Yorkshire Dales and elsewhere. A standard section is 900mm wide by 2.8m long, made of 38mm hardwood decking joined with two mild steel bars, and weighs 101kg. Sections are looped at each end for joining with a hinge pin, with metal pickets to secure in the ground. The trackway can be supplied with a non-slip tar and grit coating. A helicopter is needed to airlift the sections to remote sites, where they can be rapidly laid and joined. The price per section is £60 (1995 price).