Batter
Most walls are essentially ‘A’ shaped to aid stability, with their base equal to half their height, and the top width half that of their base. Walls within an area may be built to an almost identical pattern, following the local specification made during the enclosure period. However, walls in very different areas can be remarkably similar, possibly because experience has led to a fairly universal wisdom.
The basic ‘A’ shape can vary either due to the function of the wall, or because of stone type. A wall built of large stone is necessarily wider than a wall built for the same purpose in an area of small stone.
Concave faces
Cornish hedges are normally built with concave faces, as are many of the dry stone walls in the area. It seems likely that the hedge pattern has simply been copied in the local walling style. A concave batter aids stability, and may also be more of a deterrent to stock.
In the Rhossili area of the Gower peninsular, South Wales, many walls have a batter so concave that the top can be overhanging. This is achieved by careful selection of long stone, frequently with angled faces, set upside down compared to normal practice.
A spectacular retaining wall with a concave batter can be found in the disused slate quarry at the head of Cwm Ystradllyn, near Porthmadog, North Wales. The wall was built to support a waste heap and stop slates falling onto the tramway, used to transport slate from the quarry.
The concavity is achieved through the use of sloping faces, as on the Gower. Strength is achieved through the use of large stone, with the wall built of only 10-11 almost coursed layers. The capping stones are all about 6′ (1.8m) in length, and the corner stones over 5′ (1.5m) in length. Not a single stone appears to have moved since the wall was built.
Near-vertical batters
Walls of large stone frequently have a near-vertical batter, in order to fit the stone together without creating steps. If a stepped face is unavoidable, the step should be no more than a finger width, or only enough “to allow a mouse to creep along” (E. Hart, 1980). Many of the coursed granite walls of Aberdeenshire have stepped faces, but elsewhere it’s often frowned upon as giving access to stock. Alternatively, large stones can be tilted to fit the batter.
Walls occasionally have one face more vertical than the other. Stones with flatter, larger faces are used on the vertical side, and smaller irregular rubble on the other. Such walls may be built where only the vertical side needs to be stockproof, or on roadside estate walls where the better stone is used for show on the outer face.
Technically these lopsided walls are likely to be weaker than symmetrical walls. Empirical evidence suggests that the walls are more likely to collapse towards the face with the smaller, less regular stone, probably due to uneven settlement between the two faces.
Width
Large stone
The usual reason for walls being wider than normal is the size of building stone. If large boulders are being used, then the footings will often need to be wider than half the height of the wall. Many walls in North Wales, for example, are 30-36″ (750-900mm) wide at the base, but under 5′ (1.5m) high. In order to then maintain the correct batter, the top has to be wider than normal, that is, more than half the base width. The result is that the top is too wide to be crossed with top stones in the normal way, and a number of other coping styles are used. Normally the top cannot be narrowed because the batter would fail to be stock proof, and larger stones would create steps in the wall face. This example shows how differences in style are directly related to the available stone.
Excess of stone
Other wide walls are the result of an excess of stone generated during field clearance, and are known as consumption walls. The example below is one of many in the coastal area south of Harlech, in North Wales.
Perhaps the most massive and famous of these walls is the Kingswell West Dyke at Monymusk, Aberdeenshire. This wall is 27′ (8.2m) wide at the top, 6′ (1.8m) high and 500 yards (457m) long. Consumption walls generally have little more than a rough rubble top, although some care is taken with the stonework nearest the wall faces. Note that the Kingswell West Dyke has a line of carefully laid slabs which form a path along the top.
Clearance walls can be found in many areas, and are sometimes accompanied by the filling up and rounding off of corners, and the piling up of ‘clearance cairns’ in the middle of fields. A spectacular example of this practice can be seen at Wasdale Head in the Lake District. As you drive along the valley approaching the village you are confronted by what appears to be a sea of stone, and it is only as you get closer that individual walls can be identified. Many of the ‘standard’ field walls are about 6′ (1.8m) high, and about 5′ (1.5m) wide at the base, tapering to 3′ (900mm) at the top. Large walls are over 8′ (2.4m) high and wide, with other walls incorporating massive bulges. There are lozenge shaped mounds alongside tracks, and round consumption mounds in the middle of fields. These are perhaps 30′ (10m) across, and built as a circular wall about 3′ (1m) high, with the stone mounded inside.
Height
Walls can theoretically be any height, provided their bases are wide enough. As a general rule, the higher the wall, the longer and thicker the stone must be to build it. This is because with height, there is greater pressure on the lower stones, which are more likely to fracture or be forced out. However, some tall slate walls are built out of surprisingly thin stone, with walls taller than 20′ (6m) built with few stones exceeding 6″ (150mm) in thickness.
Low walls
Low walls, around 39″ (1m) high, are common in areas where cattle or lowland sheep breeds predominate. Areas include the Cotswolds, and the parts of North Wales where lower cloddiau reflect the local tradition of cattle farming. The lower height of some internal boundaries within farms reflects the lower grazing pressures of earlier times. In many areas the boundary walls of farms, known as ‘march dykes’ in Scotland, are 12″ (300mm) or more higher than the internal boundaries.
High walls
Walls may have been built higher than normal for enclosing deer, to form impressive estate boundaries, or to consume stone as described above. Some areas such as Glencoe had high walls reputedly to keep wolves at bay.
Sheep pens and smaller enclosures where stock are held in number need to have higher walls, of 6′ (1.8m) height or more, to prevent stock escaping. Many animals will jump or scramble over a surprising height when trapped, and sheep can clamber over the backs of other sheep to escape.
Fields to enclose bulls may have higher than normal walls, but most have fallen into disuse. One such enclosure has recently been restored in the Piethorne Valley, Saddleworth Moor, Lancashire. Most of the wall is about 6′ (1.8m) high including the top stones, reaching up to 8′ (2.4m) in places, especially on sections at the base of slopes. The large coverband below the top stones protrudes about 6″ (150mm) from either side of the wall, and is secured by sizeable top stones. On the inner side this prevents the bull seeing out, or climbing over the wall. The size and weight of the coverstones, and the top stones, prevents the bull from nosing them off the wall.
Other rarer agricultural uses are also possible. For example at Rhoscolyn on Anglesey, there is a wall on the cliff top which is over 7′ (2.1m) high, which was once part of a University experiment into crop protection. Sometimes high walls are found for which there is apparently no rhyme or reason.
Some of the most impressive dry stone structures are found around slate quarries. Almost certainly the largest free standing dry stone structure in Britain is Cei Mawr, which is located 1.25 miles east of Penrhyn Station on the Ffestiniog Railway in North Wales. This embankment supports the railway, and is effectively a dry stone wall with a railway on top. The embankment is 62′ (18.6m) high, around 60′ (18m) wide at the base, 16′ (4.8m) wide on top, and runs for 110 yards (100m). The original structure was narrower with a very steep batter, but with increased loads on the railway it was buttressed in the 1880s to its existing dimensions, which has a batter of about 1:4.
Foundations
Scarcement
A scarcement results when the wall is set in from the outside edge of the foundation. The resultant ledge can be any size, although it is usually 2-3″ (50-75mm). This practice is most commonly seen in parts of Scotland. What appears to be a scarcement may not always be one. Large blocky stone may need to be set in slightly, in order to maintain the batter of the wall.
There are two main arguments for using a scarcement.
- It provides good weight distribution, spreading the load of the wall over a larger area, and reducing the potential for settlement.
This will hold true so long as the scarcement stones are large enough that they meet, or nearly meet, in the middle. If the gap is greater than for standard footings, there is more chance of the heartings being forced down by the weight of the wall above, resulting in the centre of the wall settling and possibly collapsing. - It ensures that stones do not slip off the footing as the wall settles.
This is difficult to evaluate, but seems unlikely, as the second layer of stones could still slip off the first.
The advantages probably outweigh the disadvantages on wet ground, where the scarcement helps spread the load.
Extended scarcements, of footings plus one or more layers of stone, are used in the Highlands of Scotland to even out undulations in the ground. In parts of Aberdeenshire, where the large footing stones are irregular in shape, a type of scarcement is built to even out the footings with smaller stones, creating a level foundation for the walling stones.
Shiners
Normally foundation stones are set with their largest face on the ground, but in some areas they are set upright. This is common practice in granite walls and stone hedges in South West England, where the stones are known as ‘shiners’.
This method is not necessarily as unstable as it might appear, provided that the stone type used is heavy, and the stone sits on a good surface.
When rebuilding, it’s usually best to re-use shiners in the same way, as they are often difficult to use horizontally or ‘dropped’. They may be too long if set across the wall, making a step. If not quite long enough, insufficient space is left to build a good foundation for the opposite face. They can occasionally be used higher up as throughs, but usually they are too heavy to lift this high. ‘Dropping’ a shiner also means finding enough extra face stones to replace that part of the face which the shiner would have filled. You may be able to use larger hearting as face stones, but the hearting isn’t always suitable.
Away from South West England, shiners are rarer, although the bouldery walls and cloddiau of the Caernarfon-Bangor area of North Wales have sections containing shiners. Around Golan near Porthmadog there are several walls with extensive lengths of shiners, but generally thinner, ‘slabbier’ and less stable than the ideal.
Thinner shiners inevitably sit on a small surface, and are a potential weakness. However, if their use is unavoidable due to lack of other stone, or because this maintains a tradition, they can be used succesfully by building securely around them, as shown below. These techniques can be used to help secure any shiner, whatever its thickness, although blockier shiners with a good base need only be buried about 4″ (100mm) deeper than normal foundations.
Siting two thin shiners opposite each other is not recommended, as the hearting between will have nothing to bind to and will collapse, forcing the two shiners apart, unless very carefully constructed. If unavoidable, use large hearting, carefully placed.
