Above every window and door opening within the UK there is a beam for support known as a Lintel.
There are many different types of lintels that are available both natural and man made materials.
Despite the type, in the event the lintel isn’t correctly installed, or becomes damaged they can ‘fail’ which will result in structural problems within your property, including collapsing window and door openings!
What are Lintels?
Lintels are beams located above both doorway and window openings, and help to transfer the load of the wall above away from the window panes and into the surrounding wall.
What are Lintels made from?
Lintels can be made of a number of different materials, however the most common types of lintels are timber, stone or steel in older properties.
In more modern properties lintels are primarily made from reinforced concrete or prefabricated steel.
Each different lintel has its own advantages and disadvantages when used in construction.
Timber has been used as a construction material from when humans began to build houses. As a lintel it has a number of benefits that many other materials can’t match.
Timber is easy to cut, shape and fix to the wall, and is more thermally efficient than both stone and concrete. It also has the benefit of being cheap to buy and aesthetically pleasing in older properties with exposed lintels.
Lintels of this type have been found and used in properties from the 1500’s, with a number of houses from that period are still standing now, so they can certainly stand the test of time!
However, most of the problems with timber lintels centre around moisture and its subsequent effects on the structural integrity of the material.
Moisture within the lintel can cause the lintel to shrink as it dries out, this leads to cracking, and a ‘slumping’ of the wall above as it reduces in size as seen below.
If moisture is able to penetrate the timber, it can lead to a multitude of timber problems including pests and both dry and wet rot.
Timber lintels tend to also have a covering ‘flat arch’ of brickwork, which will be a common sight to any of you living in London.
The picture to the below shows remedial works that have been undertaken to a lintel as a result of the installation of new windows. As you can see the defective brickwork has been replaced where necessary.
Another natural material, stone has been in use as a construction material for as long, if not longer then timber has been.
In my opinion, the most aesthetically pleasing material, all different types of stone have been widely used for both decoration and structural support for as long as records began.
As a material for a lintel, stone is a sound choice. Most types can resist weathering from moisture and are generally very durable, as well as giving a grand look to a property.
The disadvantages of stone as a construction material are that like wood, it is a natural material. Because of this it can be hard to work out it’s exact structural capabilities, as natural flaws such as hollow pockets or internal damages can be present within that don’t show until a load is placed upon it.
Stone also tends to be expensive, both to source and shape, as well as being heavy and awkward to get into place.
Finally, different types of stone react differently to weathering, limestone and other sedimentary rocks will almost ‘melt’ over time due to the slight acidity of rain.
Man Made Materials
Now we come to the man made materials.
Concrete is one of the most versatile materials used within the construction industry. It is used for a multitude of structural components, including walls, floors, blocks and of course lintels.
Most, if not all modern concrete lintels have some type of reinforcing within them. This takes the form of steel bars or steel mesh to provide torsional (twisting) strength to the concrete.
These types of lintels are readily available direct from a factory, builders merchant or even made on site! They are versatile, available in a number of different lengths, cost effective and offer a high degree of structural support.
By being commercially produced, reinforced concrete lintels have to comply to a British Standard, meaning that it has a minimum strength and quality requirement.
This means that concrete lintels are generally uniform in strength when made in a factory, while the quality of site made lintels can vary drastically, from not enough, or wrongly placed reinforcing, to a poor quality of concrete, which will affect the final strength of the lintel.
Although the steel reinforcing provides more strength to the lintel, it does make the concrete vulnerable to moisture ingress.
If moisture can penetrate through the outer skin of the lintel and is able to reach the steel reinforcement, it leads to corrosion which means the steel expands, making the concrete spall and crack, ultimately contributing to the lintel’s failure.
Steel has been effectively used since the Victorian era, when large sections of steel were able to be mass produced.
Although more commonplace in modern construction, many steel lintels are still in situ in period properties today and are in much the same condition as when they were installed.
Steel is a material that is widely used today for structural framework in both residential and commercial construction, due to its high tensile strength and relatively low cost compared with other materials.
Steel can be treated with an impervious coating which both waterproofs and fireproofs the steel. Steel lintels are readily available in a range of lengths, and different structural strengths to suit the construction project.
Steel can span much larger distances than timber or concrete, making it the material of choice for new construction projects.
The main drawback to steel is that in marine environments or through prolonged exposure to water, if not protected properly it can corrode and lose strength very quickly, leading to serious structural problems.
What causes a Lintel’s failure?
Due to the varied nature of the materials, different stresses and strains on each type of lintel can cause failure, however the main causes are generally down to one of three things happening.
Structural movement within a building such as subsidence or heave can cause other elements the building, such as that of a lintel to move.
This is especially noticeable when one side of the lintel drops, putting more pressure on the other side of the lintel. The movement causing serious diagonal cracking around the opening, as well as cracking and damaging the lintel itself.
Changes in windows or doors
Lintels in houses constructed up to the 1930’s were designed to take a specific load, with the frames of the windows and doors below, which are usually of timber, providing a minor amount of support.
When these are changed for replacement PVCu or replaced with modern units, this support is lost putting more stress on the lintel. This can cause cracking and failure of a lintel, therefor if you are thinking of doing the same, look into whether you also need to change the lintels above the window openings too.
Damp and moisture ingress is a big problem for lintels. Three of the four lintels mentioned within this blog, are adversely affected by the ingress of moisture and as well as causing a failure of the lintel itself, it can also worsen other problems inside the property.
To conclude, all lintels have their advantages and disadvantages, however it is down to the individual project as to which is correct for your use.
By protecting the lintels from moisture ingress and other structural movement within the property you should never have to worry about the lintels above your windows and doors!