A cavity wall is one of the most reliable and energy-efficient wall systems used in modern buildings. It has become very common in homes, offices and commercial structures because it offers good thermal comfort, long-term durability and strong protection from moisture. In simple terms, a cavity wall is made of two separate walls, known as leaves, built with a hollow space between them. This space is called the cavity, and it plays a major role in how the wall performs.
In this blog, you will learn the purpose of a cavity wall, its key advantages, the complete construction process, common materials used and practical tips for site work. Everything is explained in clear and easy English so that even beginners can understand it well.
What Is a Cavity Wall?
A cavity wall consists of two parallel walls built with a gap of around 50 mm to 100 mm between them. The outer wall is usually made of brickwork and the inner wall can be made of brick or blockwork. Metal wall ties connect the two walls so they act together structurally. The cavity itself may be left empty or filled with insulation materials.
Components of a Cavity Wall
A cavity wall is made up of four main parts. Each part has an important role in the overall performance of the wall.
Inner Wall
The inner wall is the internal part of the cavity wall that faces the inside of the building. It is usually constructed using concrete blocks or bricks. This wall carries most of the structural load and provides support for floors and roofs. The inner wall also helps maintain indoor comfort by working together with insulation.
Insulation
Insulation is placed inside the cavity to reduce heat transfer. It helps keep the building warm in winter and cool in summer. Common insulation materials include mineral wool, rigid foam boards and polystyrene. Proper insulation improves energy efficiency and reduces heating and cooling costs.
Cavity
The cavity is the hollow space between the inner wall and the outer wall. Its main purpose is to stop moisture from passing from the outside to the inside of the building. The cavity also improves thermal and sound insulation. It must be kept clean and free from mortar droppings to work effectively.
Outer Wall
The outer wall is the external face of the cavity wall. It is usually made of brickwork and is exposed to weather conditions such as rain, wind and sunlight. The outer wall protects the building from the elements and gives it a finished appearance. Any rainwater that enters this wall drains down into the cavity and exits through weep holes.
Purpose of a Cavity Wall
The design of a cavity wall serves several important purposes:
1. To Prevent Dampness
One of the biggest issues in buildings is dampness caused by rainwater. The cavity acts as a barrier so water cannot pass from the outer wall to the inner wall.
2. To Improve Thermal Performance
A cavity wall reduces heat transfer. When insulation is added to the cavity, indoor spaces stay cooler in summer and warmer in winter.
3. To Increase Sound Insulation
The air gap absorbs sound waves, which helps reduce outside noise and creates a quieter indoor environment.
4. To Make the Structure More Durable
Buildings last longer because moisture and temperature changes cause less damage over time.
Advantages of Cavity Walls
A cavity wall offers many benefits for both homeowners and builders. Some of the main advantages include:
1. Excellent Damp-Proofing
The cavity stops rainwater from reaching the inner wall. This prevents peeling paint, mould growth and structural weakening.
2. Better Energy Efficiency
Because heat transfer is reduced, buildings with cavity walls use less energy for heating and cooling. This can lower electricity bills throughout the year.
3. Thermal Comfort
A cavity wall keeps room temperature stable, which makes living and working spaces more comfortable.
4. Sound Reduction
The hollow space blocks noise from traffic, neighbours and outdoor activities.
5. Strong Structural Support
The two leaves support each other through metal wall ties, making the overall wall system stronger.
6. Cost-Effective in the Long Run
Although a cavity wall may cost slightly more to build initially, it saves money through reduced maintenance and energy bills.
Construction Process of a Cavity Wall
Building a cavity wall requires careful planning and proper workmanship. Below is the step-by-step process:
1. Foundation Preparation
Both leaves of the cavity wall must rest on the foundation. The foundation width should be enough to support the two walls and the cavity.
2. Building the Outer and Inner Leaves
Bricklayers start by building the outer and inner walls simultaneously. The height of both walls must be kept equal to ensure proper alignment.
3. Maintaining the Cavity
A uniform cavity width is very important. Wooden battens or spacers are used during construction to maintain the gap until the walls rise to the desired height.
4. Installing Wall Ties
Wall ties made of galvanised steel or stainless steel are fixed at regular intervals. They connect the two leaves and keep them stable. The ties are slightly sloped to prevent water from travelling inward.
5. Adding Insulation
If insulation is required, it is placed inside the cavity. Materials like mineral wool, foam boards or polystyrene can be used depending on the project requirements.
6. Providing Weep Holes and DPC
To drain out any moisture that enters the cavity, small openings called weep holes are provided at the bottom of the wall. A damp-proof course (DPC) is also installed to stop water rising through the walls.
7. Finishing Work
Once the wall is complete, plastering, pointing and surface treatments are done as per the design.
Materials Used in Cavity Wall Construction
- Bricks or concrete blocks
- Stainless steel or galvanised steel wall ties
- Insulation boards or mineral wool
- Mortar mix
- DPC sheets
- Cavity trays
- Weep holes and vents
Practical Tips for Good Cavity Wall Construction
- Always keep the cavity clear of mortar droppings.
- Use high-quality wall ties spaced properly.
- Provide correct insulation thickness as per building regulations.
- Check vertical alignment using a plumb line.
- Ensure weep holes are clean and open.
- Protect the wall during rain to prevent mortar washout.
FAQs on Cavity Walls
1. Is a cavity wall better than a solid wall?
Yes, a cavity wall performs better in terms of moisture control, thermal insulation and sound reduction compared to a solid wall.
2. Can cavity walls be insulated later?
Yes, cavity wall insulation can be added later by injecting insulation materials through drilled holes.
3. What is the ideal width of a cavity?
Most modern cavity walls have a width of 50 mm to 100 mm depending on insulation requirements.
4. Do cavity walls reduce electricity bills?
Yes, a cavity wall helps maintain indoor temperature, which reduces energy use for heating and cooling.
5. Are cavity walls suitable for all climates?
They work best in areas with moderate to heavy rainfall and regions where thermal insulation is important.
Conclusion
A cavity wall is an intelligent and durable wall system that offers excellent protection against dampness, improves energy efficiency and provides long-lasting comfort. With proper design, good workmanship and the right materials, cavity walls can significantly enhance the performance and lifespan of any building. For modern construction, a cavity wall remains one of the most practical and effective choices.