Written by Michael Carr
The need for understanding lateral stability in the residential sector has been introduced by the age of the UK housing stock, with the changing wants and needs of homeowners, and the increased capacity to design and build more complex structures in the residential sector. The current UK housing stock is built on the backbone of Victorian construction, 22.9% of current private sector housing was built before 1919 with an additional 16.5% built prior to 1944. With nearly 40% of current homes in the UK being at least 80 years old and 75% being built before 1980, there is a need to update and renovate these properties to meet the requirements of the 21st century. (Ministry of Housing, Communities and Local Government, 2020)
Today, homeowners want larger, open plan living spaces and larger windows or openings to allow more natural light in. We work on a lot of projects with these design features here at Blue. If you are looking to remove the front, rear, or central walls of your home this article will explain the importance these walls have in not just supporting the structure above, but how these changes will impact the overall stability of the structure, and in particular lateral stability.
Lateral stability is the property of an element or structure, which resists the lateral forces applied to it. In residential properties, the external walls and the roof are the elements subjected to lateral loads, such as wind loading, and these elements need to be sufficiently supported or tied together to create lateral stability. If an element of the structure can twist, buckle, or potentially collapse due to the lateral forces applied, it is laterally unstable.
Lateral forces, in all structures, are resisted by the elements that move in the same direction as the force applied. For example, in Figure 1 a force applied on the side wall of a property, such as wind, is resisted by the front, rear and central walls of the house. This force is then transferred down to the foundations of the building and into the ground. Walls that resist these forces are known as buttressing walls. The floor joists, ceiling joists and the floorboards in your property tie the structure together allowing for the transfer of wind load acting on the side wall to the front, rear and central wall of the property. The combination of the floor joists and the walls acting together creates a lateral stability system and provides overall lateral stability to your residential property. If you are looking to remove or alter any of the structural elements mentioned above you are most likely altering the lateral stability of your property.
Are you planning on altering any of the structural elements mentioned above in your property? You will need a structural engineer to check whether the existing structure can cope with these alterations, and if not, you will need a structural engineer to design the superstructure to withstand these lateral forces. You can email us with your project at firstname.lastname@example.org.
To remove any of the elements described above, which create the lateral stability systems, you will need to introduce an additional piece of structure in its place to support the structure above, as well as maintain the lateral stability of your home. For example, if you are looking to remove a small part of the rear wall of your property, to create a wider doorway, you will likely only require a steel beam or lintel to bridge over the opening. This is because the rear wall still has the capacity to resist the lateral forces applied. This can be seen in Figure 1 where only the areas without the openings are highlighted to resist the lateral force applied.
If you are looking to remove much larger areas of the rear wall of your property you will likely need to install either a steel goalpost frame or box frame to your structure to support the rest of your existing home above and provide lateral stability. See Figure 2 for an example of a box frame. A goalpost frame or box frame goes in place of the buttressing wall in question and provides lateral stability in place of the masonry wall.
Figure 2 – Standard Box Frame Detail
Read more about goalpost frames and box frames here.
It is important to note that the size of the opening created will impact the amount of steelwork required to form it. The greater the area of the wall removed, provided it is a loadbearing wall, the more likely you will require not just a steel beam to support the wall above, but columns on either side to support the top beam, prevent the overloading of the existing wall, and the foundation underneath this wall.
Learn more about structural steelwork in our article, here.
To conclude, the walls, roof and floors of your property all combine to form a lateral stability system, which provides lateral stability to your property, if any one of these elements is removed or altered, you have the potential for lateral instability to occur. In the absolute worst case, the removal of one of these elements can cause the twisting and collapse of your property, if not adequately supported. Signs of lateral instability in a property will include cracking in the wall. The location of the cracking will likely appear at the midpoint along the supporting side wall, between buttressing walls or the structure installed to replace these walls, however, the positioning can be slightly more random as it will occur at the structural weaker points of your wall, i.e. the mortar bonding the bricks together has weakened. The bowing of walls can also occur in instances where the wall in question is not adequately supported.
If you see any of the above occurring at your property, reach out by emailing us at email@example.com with pictures of your concerns, and we will be happy to answer and arrange a site visit to inspect if necessary.