Solid walls to cavity walls, a brief history

1 Introduction
2 Early History
3 Roman wall construction
4 Medieval wall construction
5 Tudor, Stuart and Georgian walls
6 Victorian, Edwardian to WW1
7 Walls after the 1920's
8 Walls after the Building Regulations
9 Related articles on Designing Buildings
10 External links

[edit] Introduction

Solid wall (sometimes a called a massive wall) refers to a construction of a single primary material in one layer, or different layered materials that make up a solid wall thickness. As opposed to a cavity wall which is built in layers with at least a central gap filled with air or an air entrained insulation material, to improve weathering resistance or thermal performance.

Solid wall construction might be described as a simpler type of wall construction than cavity, although some layered solid wall constructions may also be relatively complex in their own way. Solid walls are usually most common in historic buildings, or agricultural / out buildings that do not have thermal performance requirements. In general cavity wall systems as we know today were not common before the 1900's.

Historically all walls were solid wall construction, made with natural stones, blocks, bricks or rubble. Other construction methods, often found on very early vernacular buildings that are made up of a single consistent layer throughout are cob, adobe, rammed earth as well as straw (bale), reed and grass, these may also referred to as solid construction.

In 2015 the UK Government reported that of the 26 million existing homes in the United Kingdom, over 8 million had solid walls or around 30%, in 2020 the UK Governments "Household Energy Efficiency detailed release" reported that 9% of all properties with solid walls were insulated.

[edit] Early History

Whilst there are many fine line between what constitutes an earth, adobe, cob building, all variations are essentially all solid wall construction as well as the use of straw, reed and grass in combination as natural found materials. Some of the evidence suggests variations on these construction types to have existed as early as 10,000 BCE or before, during the Paleolithic period in parts of Africa. The earliest solid wall adobe buildings are indicated to have been built around 8500 BCE, whilst the oldest existing and standing adobe building is known as the Granaries of the Ramasseum in Egypt, built by Ramses II around 1,300 BC in Western Thebes.

In the UK the earliest dry stone solid wall buildings would have been built during the Neolithic period, and would have been made up of two layers of stone, facing each side and packed with smaller infill stones. Scottish blackhouses as an example, date from around 3000 BCE, built with dry stone solid walls of over half a metre thickness, and a timber turf roof. Built to house crofters and their livestock during harsh weathers, these buildings were built as solid walls without an earth or lime mortar.

Although variations on solid earth building that may constitute as cob (the term is from the 1300's) probably existed earlier across the globe, the earliest solid cobwork walls are said date from around 1100's. These were called tabya and built in Maghreb and al-Andalus (as described by Ibn Khaldun in the 1300's). Whilst other examples, perhaps from the 1200's such as the great Mosque of Djenné, in Timbuktu or the local Togo houses, constructed of solid walls made of packed mud and straw or as bricks dried in the sun, stacked and rendered.

[edit] Roman wall construction

Although there is some evidence that lime was used as a plaster by the Egyptians, it was the Romans who moved from creating dry stone walls (or Cyclopean) walls, onto to sun dried brick walls. These solid walls were built with a base or socle of massive stone upon which sun-dried mud bricks were placed and bonded together with mud, to create solid one or two layer brick walls. It was through the development of a mortared rubble construction called opus caementicium that the Romans moved towards solid walls with roman concrete construction, which was quicker to build with. By around 150 BCE the Romans commonly used lime as mortars to build solid stone walls. These walls were also solid but made up of two layers built concurrently for speed, firstly an inner core of small stones in mortar (caementa) and then a facing layer of stoneor brick. Different names were given to the different facing finishes through the different period; Opus incertum a small blockrandom pattern, Opus reticulatum a rectilinear horizontal pattern of stones, Opus testaceum a brick faced concrete and Opus mixtum rectilinear strips of stones and bricks.

A significant number of Roman remains from forts to amphitheatres and to gateways and temples can still be found around the UK, any of which highlight their use of solid stone construction, whilst some near complete buildings can also be found. The lighthouse at Dover Castle, of the old Roman port of Dubris is one of only 3 remaining and still standing Roman lighthouses in the world, and made of solid stone with mortar, as well as largest surviving gateway of Roman Britain at Colchester. It is worth noting that although many Roman walls may have been constructed as solid layered finished walls, in his monumental set of books, De architectura (On Architecture) Marcus Vitruvius Pollio, wrote possibly the first handbook for Roman architects and indeed possibly the first mention of the benefits of adding a cavity.

“…if a wall is in a state of dampness all over, construct a second thin wall a little way from it…at a distance suited to the circumstances…with vents to the open air…when the wall is brought up to the top, leave air holes there. For if the moisturehas no means of getting out by vents at the bottom and at the top, it will not fail to spread all over the new wall.”

Marcus Vitruvius Pollio, De Architectura; The Ten Books on Architecture, Book VII, Chapter IV, On Stucco Work in DampPlaces; Translated by Morris Hicky Morgan, Harvard University, Harvard University Press, 1914. Vitruvius wrote in the time of Augustus (63 BC – 14 AD) and it is believed that he wrote this around 15 BC.

“this we may learn from several monuments…in the course of time, the mortar has lost its strength…and so the monuments are tumbling down and going to pieces, with their joints loosened by the settling of the material that bound them together… He who wishes to avoid such a disaster should leave a cavity behind the facings, and on the inside build walls two feet thick, made of red dimension stone or burnt brick or lava in courses, and then bind them to the fronts by means of iron clamps and lead.”

Marcus Vitruvius Pollio, De Architectura; The Ten Books on Architecture, Book II, Chapter VII, Methods of Building Walls, 15 BC.

[edit] Medieval wall construction

After the fall of the Roman Empire around 500 CE and into the Middle Ages, solid stone wall construction continued as a prevelant building material throughout Britain. Medieval builders had a good understanding of engineering and of solid wall construction, often building large temporary timber structures to keep stone walls in place as the lime mortars set, creating increasingly sophisticated Medieval Architecture. A large number of churches were built prior to the battle of Hastings in 1066, many of which stand today, are some of the oldest buildings in England and most are solid wall construction of stonewith lime mortar. The oldest is likely to be Beehive cells a monastic centre Eileach an Naoimh, Argyll, Scotland or St Martin's Church, Canterbury which is the oldest church building in England, and still being used.

During and after the Norman conquest, William the Conqueror ordered the construction of a vast number of castles, towers, cathedrals and churches across his realm, almost all of which were solid wall stone and most made from Caen stone brought from France. The best known examples of these are Norwich, Lincoln and Richmond Castles, Canterbury Cathedral,, Westminster Abbey and the Tower of London. In general the stone in most Medieval castle walls was built within a wooden frame designed to hold it in place while the mortar dried, in some cases for thicker walls, a cavity may have been introduced though it would usually have then been completely filled with rubble. In some examples very wide cavities were created between two single stones walls to house a thin stair case or rampart.

[edit] Tudor, Stuart and Georgian walls

One construction method that stems from the Medieval period and flourished in Tudor times is the half-timber framed housewith a wattle and daub infill. Whilst one might not necessarily describe this type of wall build-up as solid, because of its lightweight nature compared to stone, and despite being made up of different layered materials it is a full depth, through or solid construction. It was usually employed as part of a timber frame building as the infill between the framing elements. Wattle was substrate for the infill, usually wooden strips or thin branches, reeds, grasses or vines woven to form a plate spanning between and fixed to the frame. The wattle substrate was then covered with daub, made up of a combination of binders, clay, lime, chalk dust, etc, aggregates, subsoil, sand, crushed stone etc and reinforcement such as straw, hay and other fibrous materials creating a solid build-up between structural members also full depth, or covered internally.

Cob buildings, a single material solid wall construction method started to appear in parts of Devon, Cornwall and Walesaround the 1400's, at the tail end of Medieval Britain into the Tudor period. This mixture of sandy sub-soil, clay and straw was often shuttered in place creating walls of half to one meter thick, wide enough to create a raised trail for livestock to walk over, thus stamping down the mixture to compact it. It was finished with a lime render and then a lime wash externally as wellas in some cases a lime plaster internally creating a breathable hygroscopic massive solid wall build up.

In terms of stone, rubble, flint and brick constructions these generally remained solid throughout this period, although two layers of construction was relatively common, such as stone rubble externally and brick internally, the cavity between was normally filled with a rubble and lime mix and the occasional bonding stones joining both layers.

[edit] Victorian, Edwardian to WW1

It was not until some time into the Victorian period that walls with two wythes (or vertical layers) and a gap as found in cavity wall construction started to appear. Whilst the book An encyclopaedia of architecture: historical, theoretical, and practical written by Joseph Gwilt was first published in 1842, indication seems to be that it only included an illustration of a cavity wall in the later edition of 1899, describing different brick ties.

It is likely that the brick tax which was only repealed in 1850 would have impacted any earlier developments, particularly as in its later years maximum brick sizes were stipulated to control tax avoidance through the manufacture of larger bricks. There is some evidence to suggest that a few early Victorian buildings used longer stones to tie across the two wythes of early cavity walls, though qiite quickly bespoke tiles, bricks, wrought and cast iron ties developed as early as 1890. The book on Building Construction by Professor Henry Adams published in 1906 illustrates a number alternatives to the early glazed brick tiles which included metal ties more akin to modern cavity ties.

[edit] Walls after the 1920's

Familiarity with cavity walls increased by the 1920's, however anomalies exisited that prevented their uptake across the building stock for another 10 years or so, as described here by Historic England.

"In early cavity walls both the masonry leaves and the cavity can vary considerably in width, from 100mm wide to less than 50mm wide. In cheaper buildings, two single skins of brickwork would often be separated by only a 50mm cavity but it was nevertheless recognised that the thicker the masonry and the wider the gap between the leaves, the more effective the protection against driving rain and the warmer the enclosed air space. The London Building Byelaws of the early 1920s made it compulsory for one leaf to be a full brick wide and this may be part of the reason why relatively few cavity walls were built in London at this time. Where the outer skin is stonework, the cavity width will often vary considerably due to the inherent variability of this material."

There are differing estimated periods from when buildings were likely to have included a cavity for example the Energy Savings Trust points out "If your house was built after the 1920s, it is likely to have cavity walls. A cavity wall is made up of two walls with a gap in between, known as the cavity; the outer leaf is usually made of brick, and the inner layer of brick or concrete block. Pre-1920 older houses are more likely to have solid walls." Where as others put the date more specifcally 1929 and others yet later in the 1940's, mainly because uptake dramatically across the UK, with for example Wales later still. UCL and BRE reported in 2021 that half of the cavity wall dwellings in England were constructed between 1945 and 1980, with only approximately one third constructed after the 1980's.

[edit] Walls after the Building Regulations

The first set of national building standards were introduced in the Building Regulations 1965. These were a set of prescriptive standards that had to be followed. In the 1970's cavity walls construction with around 25mm of insulation was common practice and almost standard. The Building Act 1984 brought fundamental changes to the building regulations regime and it was not until the 1990's that cavity walls and cavity wall insulation were compulsory, with the level of insulation gradually increasing every few years to todays standards.