Cavity formers – also known as cavity closers, window formers, or frame formers – are vital components in new build construction. Whether you're working with masonry, timber frame, or steel frame systems, these elements help future-proof your development and streamline the installation of windows and doors.
While we’ve previously discussed the role of cavity closers in general construction, this article focuses on how they can significantly enhance project efficiency – particularly for developers, architects, and builders.
Cavity closers deliver two key advantages:
- They protect the property against water ingress, damp, condensation, and thermal bridging.
- They act as a built-in template for window and door installation, ensuring correct sizing and simplifying future fit-outs.
Why Are Cavity Closers So Important in New Build Developments?
Beyond keeping your project on track, cavity closers bring several high-impact benefits:
Exceptional Thermal Performance
Cavity closers offer excellent thermal insulation around openings, reducing heat loss and making them the most reliable method for sealing cavities. This ensures long-term energy efficiency.
Part L Compliance Made Simple
To meet Part L Building Regulations, new builds must achieve high energy efficiency standards – and using insulated cavity formers is a straightforward way to comply.
Modern properties must also be designed to prevent issues such as condensation, cold spots, and mould. Incorporating cavity closers early on plays a key role in minimising those risks.
Meeting Tight Deadlines
At Mumford & Wood, we work closely with developers, contractors, and architects to deliver exceptional outcomes within strict timelines. Our cavity closers help speed up construction schedules by reducing on-site errors, allowing windows and doors to be fitted precisely and quickly – even at a later stage.
Additional Benefits of Insulated Cavity Closers
Cavity closers (also referred to as window formers) provide enhanced project outcomes, including:
- Quick and simple installation
- Reduced risk of mould and condensation
- Green Guide A+ rated
- Low GWP (<5), zero ODP
- Prevention of cold bridging
Key Functional Benefits
Reduce Heat Loss
To meet Part L energy standards, cavity closers must achieve a minimum thermal resistance of 0.45 m² K/W. Cavity formers prevent heat from escaping through uninsulated wall cavities, helping the building retain warmth and reduce energy bills.
Prevent Water Ingress
Water can seep in around the edges of the window and door without proper sealing. Cavity closers provide a built-in damp-proof course, reducing the risk of internal damp and condensation.
Flexible to Your Build
Our cavity closers can be manufactured as 2-, 3-, or 4-sided frame kits, tailored to your specific window or door requirements, and are available in a wide range of cavity width options.
Faster Window Installation
By forming the aperture early on, cavity closers allow window installation to be completed later in the build. This speeds up the overall installation process and creates less disruption on site.
Enhanced Fire Safety
We offer both standard and fire-rated cavity closers, which can resist fire for up to 30 or 60 minutes, helping you meet Part B Building Regulations on fire safety.
Why Choose Mumford & Wood?
At Mumford & Wood, we supply BBA-certified, bespoke cavity formers tailored to your exact specifications and priced competitively. We understand that planning ahead is critical, and our formers are designed to integrate seamlessly with your development plans – reducing error, cutting waste, and maintaining compliance.
How to Order
To request a quote for cavity closers, contact our team and share the following:
- Project drawings with overall height and width
- Fire-rated requirement (if applicable)
- Check the reveal requirement
- Cavity width
You can also visit our showroom to speak to our specialists in person and explore our full range of timber products.
