Walls (External) - Parts of a Building
This post is part of a series of notes and guidance about Buildings.
Walls. You might imagine this to be one of the simpler elements of building, that everyone will understand. And you would be right, but here we are not going to define 'wall', but we are introducing the two main types of traditional masonry walls that you are likely to have in a house you purchase, depending on the respective age.
Please Note: other types of wall including framed structures (timber, metal, concrete); stone (flint, rubble, dressed); earth (cob; witchert or wychett) and a host of other non-traditional construction methods will be covered in separate posts.
In most buildings locally we encounter masonry walls, either 'Solid' masonry walls or 'Cavity' walls. Solid walls for main house building in our area will generally date the building back to pre-1930 and Cavity walls pretty much for every main wall built after 1930; although there can be a few years of cross-over between the two.
So what are the differences between Solid and Cavity walls? After all a cavity wall still feels and looks pretty solid!
By a Solid wall we mean that it was built as a 'single skin', normally of brickwork although that might be covered with render or tiles externally and more often than not plastered internally. The bricks will tend to be laid with a brick bond that forms a 9 inch thickness.
By a Cavity wall we mean that it has two skins of masonry, each being about 4 inches (100mm) thick, and the two spaced apart with a gap between. With the first cavity walls each skin was more likely to be brickwork, again the external skin could be rendered or have tile hanging or other cladding; and internally plaster finishes are the norm. However relatively quickly the inner skins started to use concrete blockwork and these too soon became more sophisticated with thermal improvements. However, whatever the material, the two skins need to be tied together to give overall stability, the ties are normally metal and known as 'wall ties'. The gap between the skins gives the name : 'cavity' : and the cavity can vary in width. Sometimes as little as 1 inch (25mm) cavity, but more commonly 2 inches (50mm), 3 inches (75mm) or 4 inches (100mm)... the width of the cavity tended to increase as requirements for better thermal insulation requirements arrive with more modern buildings. So we tend to find an overall wall thickness of 10 inches (250mm), 11 inches (275mm) or 12 inches (300mm).
We will look at brick bonding at another time, as that is worthy of a post on its own. Also to note, the wall thickness suggested above excludes the thickness of any external finishes and internal plastering so when physically measured the overall thickness will be more than the figures stated.
A pre-1930s house with Solid Walls
So what are the advantages, disadvantages and risks of the two types?
The advantages of Solid walls are limited, which is why they stopped being used around the 1930s, so in general cavity walls are going to be regarded as 'improvements', and the nature of cavity walls hasn't remained unchanged so we see more 'improvement' over the years.
The one advantage that of a solid wall, that was lost with the introduction of cavities, was that they do not rely on the separate ties to make them stable. This flags the first disadvantage of older cavity wall construction, as the ties used were metal there is the risk of these corroding (rusting) and so then the strength is lost and the two skins are no longer tied together effectively and so may have a loss of stability. As time moved forward the quality control of wall ties has improved, such as using galvanised metals that are less prone to rusting, and then improving on that further with better galvanisation processes and then a move to stainless steel.
We can next consider the key advantages gained with the progress of cavity walls:
less chance of water ingress - a separation between the outside skin and the inside skin means that water should not be able to travel across (although it doesn't resolve the problem completely, as water can still find a path to soak across where cavities are 'bridged' with debris or wall ties or insulation).
thermally better - a separation between the outside skin and inside skin also means better thermal properties from having the cavity. Even the air space of an uninsulated cavity provides an improvement over a solid wall, but of course that improves further by adding thermal insulation materials into the cavity, and then as the thickness of the cavity gap increases, more and more insulation can be added. The benefits of thermal insulation are further exploited with developments in the modern insulation materials, which have become evermore efficient.
A modern house with Brick-faced Cavity Walls