Walls can be used to define the boundaries or different areas within the site. Retaining walls can be built to make changes of level within the site. Dry stone walls provide a valuable habitat for invertebrates, amphibians, reptiles and small mammals which shelter or hibernate in the crevices. Walls also create conditions of shelter and warmth, shade and damp, providing microhabitats for various organisms.
Walls can be built out of any suitable material on the site, including stone, brick and building rubble, or a combination of materials. Concrete rubble from hard standings can be broken up into pieces for use like stone, and weather to a reasonable appearance after a year or two.
Coping stones on dry stone walls are normally mortared in position, to prevent them being dislodged or removed. On sites where vandalism or theft is possible, the wall itself may have to be mortared. To retain some habitat value, leave some crevices unmortared, leading into the centre of the wall.
The dimensions of a free standing dry stone wall will depend on the available stone, and the purpose of the wall. A bottom width of about 600mm should be sufficient for a wall 1m high, increasing to a width of 900mm for a wall 1.3m high. Start by marking out the base of the wall, and digging out a footing deep enough to take the largest stones, which will form the foundation. Stones or rubble are then built up in layers, the largest at the bottom, trying to fit each stone so that it is solid and crosses a gap. The middle of the wall is carefully packed with small stones as work progresses. Occasional large stones or ‘throughs’ can be placed across to tie the outer faces together.
Retaining walls are built in a similar way, backfilling as work progresses. High retaining walls holding back a large amount of backfill may be a hazard to safety, so a maximum of about 600mm height is probably suitable, especially where the walling material is variable or vandalism likely.
For further information see Dry Stone Walling. Mortared walls, built of stone, brick, block or a variety of materials, may be preferable to dry stone walls to discourage vandalism or for safety reasons. The construction of garden walls is well described in the many books available on garden construction, for example The Small Garden, Brooks, John (1977).
Effective retaining walls can be built out of old tyres, stacked either to make a near vertical wall, or as a sloping bank. The latter makes an irresistible play feature for children, and planting in the pockets is almost certainly doomed. Painting the tyres is a more reliable method of brightening them.
Wall building is best done near paths, site entrances or prominent parts of the site, where they will either have a function to mark a boundary, improve the site appearance or to direct users, and where the walls are overlooked to deter vandalism. Using piles of existing stone or rubble to build walls with no particular purpose other than habitat improvement may be self-defeating, as the pile of stone is likely to be a more valuable habitat than a wall, and is also less likely to be vandalised.
Mortared walls in community gardens and other supervised sites can incorporate handmade tiles, mosaics, sculptures and so on, and their building can be linked with local arts projects. Crevices or specially-made bricks can be incorporated for animal homes.
As historical features containing interesting geological examples, walls in urban areas have great potential for study and interpretation. The Geologists Association has promoted ‘The Wall Game’, to encourage the use of walls for education. new walls can also be built out of a variety of local stones and reclaimed building material. This may be a good way of preserving fragments from derelict buildings which have to be demolished for safety or other reasons, thus keeping a link with the past.
Native or introduced climbing plants can be grown up walls in almost any situation, to provide the benefits of greenery and flowers for people and wildlife. Of the native plants, ivy is self-clinging and common everywhere, and is of great value for invertebrates, birds and other animals. Consult a gardening reference book, for example Gardening on Walls, Grey-Wilson, Christopher and Matthews, Victoria (1983) for information on introduced climbing plants.
