How to Choose the Right Cavity Closer for Your Project
Cavity closers, also known as cavity closures or wall cavity closers, are key components in any building project. They create a barrier in the cavity wall that keeps out damp and maintains contiguous insulation across the opening around window and door reveals. With numerous options available to suit different construction types, installation stages and performance needs, choosing the correct cavity closer means understanding the specific requirements of your project. Overlooking details like cavity width, fire safety or material compatibility can lead to compliance problems or costly rework down the line.
So, what do you need to look for to make sure your build is up to standard and built to last?
What to consider when selecting a cavity closer
Are the closers being installed at first or second fix?
The type of cavity closer you need depends on the installation stage. First fix refers to the primary construction phase, when the building’s structure is still going up and the windows have not been installed. For this stage, pre-formed cavity closers are well suited, as they integrate directly into the wall, bonding with the brickwork and mortar to create a lasting, secure seal. Pre-formed options help guide bricklayers, keeping window and door openings consistent and accurate, which can speed up construction.
In second fix installations, where the building work is already complete and the openings are being prepared for final fittings, pre-formed closers are not suitable. Instead, multi-width cavity closers or cut lengths work better, as they can be trimmed to fit the specific cavity width and inserted into the cavity. These are secured with grab adhesive or tacks, giving a solid seal that keeps the finished wall intact.
What is the size of the cavity?
Determining the cavity width, the measurement from the inner to the outer leaf of masonry, is the starting point for selecting a properly fitting cavity closer. Cavity widths vary with the building’s design and insulation requirements, so an accurate measurement matters for a snug fit. The wrong cavity closer size can lead to poor insulation and dampness, which affects both the building’s durability and its energy efficiency.
For standard cavity sizes between 50mm and 300mm, pre-sized closers in fixed dimensions simplify installation with no need for adjustments on site. For unusual or unique dimensions, multi-width cavity closers with pre-cut grooves can be trimmed to the exact size needed on site. Alternatively, for non-standard sizes or mixed size cavity closers, we are able to manufacture bespoke made up frames to suit your requirements.
What materials are used in the building structure?
The materials used in your building’s structure are an important factor when choosing a cavity closer. Different construction types, like brick and block, timber frame or steel frame, may need specific cavity closers for a secure fit and reliable performance.
Brick and block walls work well with a wide range of cavity closers, as they give a stable, solid base that lets the closer fit securely and form an effective barrier against moisture and draughts.
Timber frame constructions benefit from insulated cavity closers, as timber is more vulnerable to moisture. These closers help keep damp away from the timber, improving the structure’s longevity and energy efficiency.
Steel frame builds need cavity closers that address thermal bridging, as steel conducts heat. Closers designed for these builds help manage that heat transfer, reducing the risk of condensation and maintaining the structure’s energy efficiency.
How much insulation does the cavity closer provide?
The insulation inside the closer is what keeps the cavity thermally continuous where the wall is broken for a window or door. Every cavity closer Subframes supplies has an insulated core that runs the full depth of the cavity, so heat is not lost around the opening and the inner face stays warm enough to keep condensation and mould off the reveal.
The amount of insulation matters most on high performance builds and on constructions prone to thermal bridging, such as steel frame. A closer with a thicker insulated core holds more of the thermal line, which helps the opening meet the fabric standards set out in Building Regulations Part L (Conservation of Fuel and Power). If you are unsure how much cavity closer insulation a detail needs, the closer should at least match the thermal performance of the surrounding wall insulation.
Does the project require fire-rated cavity closers?
Fire-rated cavity closers are designed to slow the spread of fire and smoke through cavity walls for at least 30 minutes, which adds an important layer of protection in multi-storey buildings and certain higher risk structures. This type of cavity closer is typically required under Building Regulations Part B (Fire Safety), which sets out the fire safety standards for residential and commercial buildings.
These regulations specify that buildings over 18 metres tall, or those with higher occupancy and fire risk, should use fire-rated materials in cavity barriers to seal the cavities around window and door openings. Choosing a cavity closer with a certified fire rating that meets the architect’s specification means you meet these standards and keep the build compliant.
Explore our range of cavity closers
Subframes UK is the largest trade supplier of welded and mechanically jointed cavity closers in the UK, with products to meet the needs of modern construction projects, from small renovations to large scale commercial builds. That range is reflected in the trusted brands we work with, including Cavalok, Dacatie, Kingspan and Timloc.
We manufacture our own cavity closers at our Midlands factory. Every product we make meets current building regulations and gives strong thermal efficiency, across both commercial and domestic work. You can see the full range of cavity closers we supply, or contact the team on 01773 590100 or at [email protected].
