Cavity closers are an essential part of any cavity wall. A cavity closer’s main benefits are to prevent heat from being lost through the gap and to act as a seal to prevent external water and damp from getting into the cavity wall and the building.

Cavity closers can be alongside a range of different constructions, including masonry, timber frame and steel frame systems.

Now that we have a brief introduction of cavity closers and their function, let’s dive in and find out more information, including what they are, exactly, and how to fit a cavity closer.

Table of contents:

What is a cavity closer?

SuperCLOSE Insulated Cavity Closer

A cavity closer fits within a cavity wall, where windows and doors are fitted. Cavity closers are required for a number of reasons within a building to protect it from various factors, including water ingress, damp, heat loss and condensation.

The cavity closer acts as a seal, preventing external water vapour and damp from entering the cavity wall and the building, whilst also preventing heat from being lost through the gap. Cavity closers can be used in a range of different constructions, including masonry, timber frame and steel frame systems.

Diagram of an Arc cavity closer.

Insulated cavity closers

Insulated cavity closers have the same features as most cavity closers, meaning there is a damp proof membrane to help prevent the ingress of moisture (which causes damp and condensation issues), as well as PVC extrusions and a flexible seal.

However, an insulated cavity closer also features a layer of insulation, such as XPS insulation, to further increase the thermally insulating capabilities of the cavity closer. Insulated cavity closers are particularly useful in projects where sustainability, minimal energy consumption and insulation are key factors.

Which brands offer cavity closers?

Brands such as Timloc, Manthorpe and SuperFOIL offer cavity closers in a range of widths and specifications. Single flange cavity closers, double flange cavity closers, multi-width cavity closers and fire rated cavity closers all feature in Insulation Superstore’s comprehensive range.

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Why do you need a cavity closer?

Cavity closers have three main priorities when installed around a door frame or window frame within a cavity wall:

  • To prevent water ingress
  • To reduce heat loss
  • To improve fire safety

Water ingress diagram.

Prevent water ingress

Firstly, a cavity closer will prevent the ingress of water occurring around the edges of a window or door, acting as a damp proof course, reducing the potential for damp, condensation and mould from occurring. This is important to ensure the building complies with Building Regulations Part C (resistance to contaminants and moisture).

Thermometer diagram.

Reduce heat loss

Secondly, cold bridging commonly occurs around windows and doors, where heat transfer is much greater, significantly reducing thermal insulation.

The cavity closer prevents thermal loss from occurring within uninsulated cavity walls, which is important for Building Regulations Part L (conservation of fuel and power) because it helps to reduce the amount of energy used to keep the building warm. Part L building regulations are becoming increasingly important as the drive to become more sustainable and conserve more energy grows.

Fire safety diagram.

Improve fire safety

Thirdly, a cavity closer will help to improve the fire safety of the building, particularly when the cavity closer is specifically a fire-rated cavity closer – fire rated cavity closers can prevent the spread of fire for 30 minutes or an hour, depending on the fire-rated product you choose.

Fire-rated cavity closers can help to ensure your building is compliant with Building Regulations Part B (fire safety).

How to fit a cavity closer

Cavity closers can be fitted both before the brick wall has been built, known as the first fix, or after the wall has been built, known as the second fix.

Here’s a general overview of the process:

REDSHIELD Cavity Barrier Double Flange cavity closer

Step 1: Measure and prepare

Measure the width of the cavity to ensure you select the correct size of cavity closer. Cut the cavity closer to the appropriate length, leaving a small gap (usually around 10mm) to accommodate any potential movement or settling.

Step 2: Positioning

Place the cavity closer horizontally across the cavity opening, ensuring it sits flush against the inner and outer walls. If necessary, use spacers or wedges to hold it in place temporarily.

Step 3: Fixing

Secure the cavity closer in place by fixing it to the inner and outer walls using suitable fixings, such as screws or wall plugs. Ensure the fixings penetrate both the closer and the wall material adequately for stability.

Step 4: Sealing

Seal any gaps or joints around the cavity closer using appropriate sealant to prevent the ingress of water, drafts, or pests. Pay particular attention to the junctions between the cavity closer and the walls to maintain insulation integrity.

Step 5: Check and finish

Once installed, inspect the cavity closer to ensure it is securely fixed and adequately sealed. Trim any excess material, if necessary, and check for any remaining gaps or areas requiring additional sealing.

As with all products, each cavity closer installation process will vary slightly depending on the manufacturer, but a cavity closer installation guide should be found within the packaging of each product when purchased. Check out the video below for a guide to installing Kingspan Kooltherm Cavity Closers, and to see more about how the cavity closer installation process works.

Final thoughts

Cavity closers are components used in construction to fill the gap between the inner and outer walls of a building where a cavity wall exists. They are needed to ensure the energy efficiency of buildings by minimising heat loss and preventing moisture penetration.

What’s more, they help to maintain structural integrity and provide a barrier against drafts, noise, and pests.

Bottom line:

Overall, cavity closers play a crucial role in creating a well-insulated and comfortable indoor environment while enhancing the durability and performance of the building envelope.

Unsure of which cavity closers are best suited to your project? Call our team of experts on 01752 692 206 and we will be more than happy to offer product recommendations and advice.

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