Decking Ideas – Adding a Bridge
ADDING A BRIDGE
As well as being used for its traditional purpose of crossing water, a bridge can also be installed as a link between two decks or could even create a short cut across a flower bed.
A simple bridge can be built using straight timbers, but why not be more adventurous and build a visually more exciting arched construction to make a real focal point? Building a bridge is the same as building a narrow deck and providing that the span to cross is short, joists can be used in the construction. The obvious disadvantage of decking joists is the lack of a curve to produce the small humpback bridge look; these shaped joists are available from specialist timber merchants who can be found in your local directory.
The design should allow for the width of the crossing and an overhang either side for the starting point.
The smallest joists should be at least 150mm by 50mm for a 2m span, with ideally a 90cm overlap onto the land either side of the stream. A larger overlap will be required if the soil is sandy or subject to erosion. Joist spacing should be closer than on a deck — 30cm on centre as a maximum will be strong enough. The treads should be wide enough for people to walk across without the feeling of a tightrope — 60cm is the minimum width, but 90cm will feel more comfortable to walk on. All grooves must go side-to-side across the bridge to ensure a non-slip surface. Extra maintenance to keep the treads clean will be necessary to avoid accidents. Any cleaning compounds used must be safe as they will fall into the waterway
1. Measure out the first side of the deck by laying the joist across the stream to ensure the correct length is cut. This will also give the position of the footings.
2. As you would with a deck, build a frame that is the width required for the bridge, ideally no less than 60cm. Use a central joist to add strength to the frame.
3. With the frame complete addto prevent wobble — they will also increase the ridgidity of the frame. A bridge that moves as you walk across it is not desirable.
4. With help lift the frame into position and level both ways. Install two posts as on the decking by digging in and concreting in place. Bolt the posts to the frame with twoor per post for added strength. Check for level as you go. The bridge must be level to create a safe walkway. Drainage is not a problem as it is with a deck as the boards are so short that the water will drain away immediately anyway. As in other decks use preservative on all cut surfaces.
5. With the other end secured to the posts fix the bridge to the deck by toe-nailing the frame to the surface, using longto go through the deck boards into the joists.
6. Fixing the first tread, use a small block to create an even overhang at the front of the bridge. Space each board 5mm apart to allow for movement in the timber
7. Use self-drilling screws on all treads to stop the boards splitting. The last tread may have to be cut to fit. If its width is reduced too much swap it with the next tread in.