Property Surveying Blog
In this blog post, I am going to be looking at roof coverings. The whole purpose of these as you know is to keep the inside of the property dry and in a good condition. A leaking or faulty roof covering is one of the easiest ways that water can penetrate your property.
A quick look at historic buildings tells us that a number of coverings were used prior to the introduction of modern construction materials.
However, some coverings, like the clay tile are still in use today, on a number of properties due to their versatility and effectiveness.
Less often seen are coverings such as Thatch or timber Shingles, which due to their relatively short lifespan and high cost to install, are most often saved for period construction projects, such as listed properties.
In this blog I will be discussing a couple of the most common roof coverings seen in London today, namely, Slate on period properties, Clay tiles on 1930’s properties and interlocking concrete tiles, which has been applied to many new builds, and retrospectively fitted on a number of period properties.
Slate tiles have been around for almost as long as we’ve been building houses. They gained popularity as a material through their use in Wales, and other communities located near large deposits of slate.
Slate was used in thick continuous slabs, before it was realised that it was a very suitable material for properties in other parts of the country.
The industrial revolution in the UK meant that slate tiles were made more available to the rest of the country due to the expansion of the canal network.
Although originally the slate would have been solely from Wales, now a large proportion of slate comes from countries such as Chile, China and Spain, which are cheaper than original Welsh slates.
This type of roof covering is long lasting, between 50-100 years if installed correctly and relatively easy to source from many building suppliers throughout the country.
The other benefit of slate tiles are the appearance, they can come in a wide range of colours, thicknesses and sizes, leading to a sophisticated or simple look, depending on the preferences of the homeowner or house builder.
In addition, when period properties were built, the roof timbers and walls were designed to support a certain amount of weight or “load”. A roof covering of slate tiles is typically around 800 to 1500 pounds per square meter, which is less than the equivalent interlocking concrete tile roof. This means that they are one of the tiles of choice for period properties and can avoid the roof from bowing or undulating, which is a common issue caused by heavier roof coverings.
However, as with any building material, slate tiles do haver a couple of disadvantages. Installation is key to having a slate roof. Due to their nature, slates need to be installed properly, even being “triple lapped” in places, meaning that there are three layers of slate in places to prevent water ingress. Without the tiles being installed professionally and by a roofer who knows their trade, you could find yourself with a very expensive roof, with a very short life span!
In addition slate tiles are fragile, they break easily if walked on, or if something falls onto them. This can lead to a higher chance of accidental cracking and therefore water ingress. In addition, as they are manufactured from a natural material, they are more prone to weathering and natural defects.
As a rock, slate is formed in layers, they are therefore most vulnerable to something called “Freeze-Thaw Weathering” This is the process where driving rain gets into the layers in the slate and then in cold temperatures freezes causing the water to expand and lift/spall the layers off one by one.
Slate Imitation Tiles
An alternative to traditional slate tiles are tiles made of composite materials such as plastics and fibres. Not only are these made to look just like the real thing, they are are actually lighter and generally cheaper to install, making them a good alternative choice to traditional slates whilst still maintaining the look of a slate roof.
A well known manufacturer of vacuum cleaners has even made a solar powered imitation slate tile so that you can power your home and keep your roof watertight at the same time!
Clay tiles were used as far back as the roman times. They are cheap and easy to produce and are a versatile covering, moving through curves and bends with ease.
In addition they also come in a number of glazes, shapes and profiles, which makes them perfect for every type of project.
Clay Tiles are a common sight in London and the surrounding areas, most notably from houses between 1700 and the 1930’s, where they were installed just after the Great Fire of London and just prior to the widespread use of Concrete tiles.
Clay Tiles have a shorter lifespan than a well installed slate roof of approximately, however due to their relative lower cost and ease of installation, they are still a popular choice for many homebuilding projects and refurbishments.
As with Slate, Clay Tiles are equally prone to Freeze Thaw Weathering, which tends to cause the top layer of the tile to break away, resulting in the soft porous interior of the tile being exposed to the elements, allowing water ingress and further deterioration.
In addition, on older properties such as those constructed around the 1700’s, clay “peg tiles’ were used, which as suggested were held in place with a wooden “ peg” or dowel. It is only natural that 300 years later, these wooden pegs are deteriorating, causing the tiles to slip, which can lead to not only the ingress of water but also the ingress of pests and other animals such as birds.
Interlocking Tiles/ Concrete Tiles
Concrete tiles are one of the most common and widely used materials used on roofs both on new builds and retrospectively fitted to older period properties.
They are generally profiled and interlock, thereby giving a double lap of tiles that are both watertight and durable to the elements.
Like Clay Tiles they come in a number of finishes and colours, as well as imitating different types of tiles.
The disadvantages to these types of tiles are their environmental impact, with them being the most carbon dioxide intensive to produce and use, as in addition to the cement which goes into the tile, they also have to be bedded in a cement fillet at the sides and ridge or hip of the roof.
The main disadvantage however is that they should not be used on period properties due to their weight. This extra weight can cause the walls of the property to bulge outwards in a process called roof spreading, which can lead to serious structural failure.
If you are planning on changing your roof covering, plan it carefully, selecting the wrong material can lead to structural load issue and could also see a high price paid for a very short useable roof life span.