Vernacular Materials

Introduction

This page covers some of the key building materials used in vernacular building in the UK, with particular reference to the county of Devon.

Vernacular architecture is often typified by the building of structures in materials which are locally available; difficulties with transport, lack of locally available skills, and the extra cost of building with materials that have to come from a distance tends to lead to grand houses and churches or other public buildings being built with (or at least to feature) "foreign" materials, with smaller, humbler, buildings using materials that are available either on the site or at a relatively short distance.

Crucial to Devon vernacular buildings are stone, timber, cob and thatch. These materials were used for many hundreds of years prior to the eighteenth century, creating a wide range of buildings which share a truly organic relationship with their surroundings.

Stone

Although the use of mortared joints in stone was fairly common in the twelfth and thirteenth centuries for churches and the houses of the nobility, ordinary houses built mostly of stone did not become common throughout the country until about 300 years later, and even then was largely restricted to houses of manorial status or similar.

Small early stone houses were only built in any number on and around Dartmoor in Devon, where plentiful supplies of easily accessible granite were available due to the erosion of the tors - the name given to granite outcrops with which the moor is dotted.

Possibly more important than the availability of the granite was the lack of availability of other materials and poor transport in the area.

Granite is an igneous rock and is immensely strong and durable; granite from Dartmoor was not quarried to any great extent until the nineteenth century, and then principally for building lighthouse, bridges, etc. rather than houses. Houses would have been built using the "moorstone" with some dressed blocks for corners and openings; the indestructible nature of the material has meant that many of the buildings remain in this area.

Larger numbers of granite buildings are to be found further west in Cornwall, where additional outcrops of the stone occur, and again transport difficulties have prevented other materials being used. The Dartmoor buildings are in general older than their Cornish counterparts.

Timber

Timber has probably been used as a building material since man first invented tools to manipulate the component parts of the tree. Many old vernacular buildings that were of timber frame construction have been subsequently clad in stone or brick, disguising the original structure. Timber has the advantage over stone in that long lengths - on occasion up to 50 feet (over 15 metres) - could be produced which were self supporting, making it the ideal material for enclosing a reasonable size open space, as a roof member. More sophisticated techniques allowed much greater span, as can be frequently found in churches and public buildings.

As a structural material, oak was the preferred wood, being extremely strong and durable, but most of the country's oak forests were depleted by the eighteenth century and other woods including imported softwoods were then used. The oak was not seasoned for very long, and generally used within a year of felling.

The types of jointing used in the roof timbers is a valuable aid to dating vernacular buildings, and is an interesting subject for study in itself! Iron bolts or nails were rarely used (the acid in the oak accelerates rusting), joints were pegged with oak pegs made from the heartwood of the tree, which gave an equally strong fixing. Joints would generally have been cut at the carpenter's yard, and the whole structure transported to the site in pieces for assembly. Joints were marked with a system based on Roman numerals for identification.

Most medieval timber-frame buildings have large rectangular panels with braces and infilled with wattle and daub, which was a woven panel of split sticks covered in a mixture of clay, straw, hair, lime and cow-dung, as available. This was allowed to dry and plastered or limewashed to make waterproof. As bricks became more readily available, they tended to replace the daub, and any other locally available materials were also sometimes used, although protected daub - like cob - generally gave the best results.

Cob

Cob is basically a mixture of earth, clay, stones, straw, water and cow-dung with a little lime added to make it set, applied without any form of 'shuttering', and hence giving a somewhat irregular wall thickness. (My own house has a cob wall which is about 12" (30 cm) out of vertical in about 7 feet (2.1 metres), and is not unusual.) It was the traditional walling material in much of Devon, and was common in other parts of the west country, and also Cumbria in the north of England. Cob structures in other parts of the country tend to be cottages and farm buildings; in Devon, substantial houses as well as garden walls use this material, and even chimney stacks were made of it.

The oldest cob is thought to date from about 1300, although most cob buildings are thought to be of sixteenth- or seventeenth-century origin. Again, many cob buildings have been covered with plaster or cement rendering at a later date, disguising the original material.

The preparation of the cob inevitably took place close to the site of the building to be ercted. The materials were mixed with water into a workable consistency by animal or human feet before being applied to the wall; an initial layer was typically about 2 feet (60 cm) high, and subsequent layers were trodden in to the top of the wall, about 1 foot (30 cm) thick. The wall was allowed to dry for about a week before the next layer was applied. Walls built in this way were generally over 2 feet (60 cm) thick, and sometimes more than twice that. Considerable variation in drying time, thickness, etc. was caused by the weather and the quality of the local materials, and there is documentary evidence of building whole walls at one go, using both shuttered and unshuttered techniques.

The completed wall was frequently coated with lime plaster, which allowed rising damp (and the residual water from the construction) to dry out, and was coloured with white or pink limewash. Building such a wall was very labour-intensive, extemely hard physical work, and prone to be delayed by poor weather condition.

The Devon rural tradition is that cob "needs a good hat and a good pair of shoes" - i.e. protected from water at the base and top - and to this end was generally applied to a stone plinth and fitted with a thatch roof - even if it was only a garden wall. Protected in this way, cob remains a substantial part of many Devon buildings as it has for many hundreds of years.

Thatch

The word 'thatch' derives from the old English word 'thack', meaning any sort of roof covering; as the earliest materials were heather or reed or straw, the term now is restricted to a roof of vegetable material. This was the most common roofing material from the end of the Roman occupancy to the twelfth century, when more fire resistant materials became common. Thatch was prohibited from new buildings in London from the early thirteenth century, although this did not prevent the Great Fire in 1666.

The best material in terms of longevity is water reed, which may last up to 100 years, but this was rarely employed due to expense. Most commonly, wheat was and is used. Thatch forms an ideal covering for cob, as is light and flexible, ensuring that the roof load is evenly distributed on the walls. A typical thatch roof will last between about 10 to 20 years before being 'rethatched', but degrades fairly gracefully, and may be patched indefinitely. In this case, the appearance is marred by the presence of hazelwood strips which hold the repair in place.

Where access to corn is difficult - particularly the remote moorland districts of Scotland and Ireland - the thatch may be of heather or sedge, or occasionally flax, ferns rushes or bloom. Rye-straw, oats and barley were also used, rye-straw being the longest and strongest.

During the eighteenth century, thatch became considered an inferior roofing material and fell from favour to be replaced by slate and tile; this trend was reversed in the nineteenth century when it became fashionable again with the Art and Crafts and Art Nouveau movements, both of which emphasised traditional materials and craftsmanship.

Thatch remains a fairly common roofing material in Devon, offering - particularly in combination with cob - good insulation against extremes of weather; it is not common on new houses, largely because of high initial and maintenace costs. However, there are plenty of thatchers about, and plenty of business, and grants are available to aid maintenance.

Thatching was traditionally very much a local activity; even today, you will frequently find a thatcher working within a few miles of his home, and each village seems to have a thatcher or retired thatcher living in it. The craft was frequently passed on from father to son, and there is a Master Thatchers Association which aims to ensure a consistently high standard of work.

The traditional Devon style is very plain; occasionally a pattern of spars is applied to a ridge, or a straw 'dolly' in the shape of a bird is added to the ridge, but until the 'cottage orné' was introduced in the nineteenth century, decoration was not normally thought to be necessary, and tends to look 'twee'.

Bibliography

English Farmhouses by R.J. Brown
Published by Arrow Books 1982 ISBN 0 09 935380 6

Cob and Thatch by Pamela Egeland
Published by Devon Books 1988 ISBN 0 86114-816-9

Devon Building by Peter Beacham
Published by Devon Books 1990 ISBN 0 86114-852-5