Cavity Formers for New Build & Extension Projects
When you are building a new home or adding an extension, getting the windows and doors right is incredibly important. At Allwood, we supply high-quality cavity formers. These are simple frames placed into the walls while they are being built. They create the perfect, exact opening for your new timber windows and doors to fit into. By using them, you ensure your home is completely weatherproof, warm, and built to last.
Precision Cavity Formers for Faster, More Accurate Construction
Building a new home or extension requires absolute accuracy. If the gaps left for your windows and doors are even slightly off-size or out of shape, fitting the actual frames becomes a major headache. At Allwood, our precision cavity formers solve this problem completely. By acting as a solid, perfectly square template right inside the wall, they help your builder work faster, cut down on mistakes, and ensure your premium timber windows and doors fit beautifully.
What Are Cavity Formers?
A cavity former (sometimes called a cavity closer) is a ready-made, insulated frame placed into the gap between your walls while a new home or extension is being built. In the UK, modern properties are built with “cavity walls”-meaning there is an outer layer of brick, an inner layer of block, and a hollow gap filled with insulation in between. When you cut a hole in that wall for a window or a door, you expose that open, hollow gap.
How Do Cavity Formers Work?
Instead of building the brick walls first and measuring the openings later, a cavity former streamlines the sequence:
- The On-site Template: During construction, the cavity former is fixed exactly where a window or door will go. It acts as a rigid, perfectly square guide. Instead of measuring by eye, bricklayers simply build the outer brick and inner block walls tightly around it, ensuring the opening is perfectly straight and accurate.
- The Permanent Wall Seal: Once the walls are up, the former stays hidden inside the wall to permanently seal the open cavity gap. Its insulated core acts as a barrier that stops outside cold from travelling to your inside walls, completely eliminating the cold spots that cause heat loss. By keeping these wall edges warm, it prevents the condensation that naturally leads to damp and mould growth. Additionally, it creates a tough, weatherproof seal that blocks out driving rain and cold draughts, keeping your home warm, dry, and energy-efficient.
- The Perfect Fit: Because the opening is perfectly square and standardised, your premium Allwood timber windows and doors slide straight into place. This ensures a fast, airtight, and flush installation with a high-end finish.
Why Are Cavity Formers Used in Modern Construction?
In modern construction, cavity formers are a necessity because they help new builds and extensions meet strict British building regulations for warmth and energy efficiency. In the past, builders closed the open gaps in walls by simply turning the bricks inward or using temporary wooden boxes. These old methods caused major problems, as the wood would warp in the rain-leading to wonky openings-and the brickwork allowed outside cold to escape straight into the home, causing draughts, high heating bills, and black mould.
Today, pre-made cavity formers solve these issues completely by giving bricklayers an instant, perfectly straight template to build around. This speeds up the construction process and removes any guesswork on site. Because these formers stay inside the wall permanently, they keep the home’s insulation completely unbroken right up to the window frame. For your project, this means every single opening is perfectly square and standardised, allowing your premium Allwood timber windows and doors to slide straight into place with a flawless, airtight fit that keeps your home warm and dry for decades.
Who Are Cavity Formers Suitable For?
Cavity formers are a vital addition for anyone building new walls using a traditional brick-and-block cavity system. Because these formers must be put in place while the walls are actively being built, they are perfect for specific types of building projects.
Homeowners Planning Extensions or New Builds
If you are extending your home with a new kitchen diner or building a brand-new property from scratch, you want the structural shell to be perfect. These formers are ideal for ensuring your new rooms are highly energy-efficient from day one, protecting your home from the damp British weather and keeping your heating bills down.
Self-Builders & Architects Aiming for a High-End Finish
When you invest in bespoke architectural joinery, the structural preparation needs to match that quality. These formers are perfect for projects featuring our premium Allwood timber windows or wide bi-fold doors. They guarantee that every opening is square and accurate, so your handmade glazing fits flush and works smoothly without relying on ugly foam fillers.
Contractors and Bricklayers Looking to Save Time
For the tradespeople managing your building site, these pre-made frames remove all the guesswork. Instead of spending hours measuring openings by hand or making temporary timber boxes that twist and warp in the rain, builders get an instant, solid guide to lay bricks against, which speeds up the entire build process.
How Our Cavity Former Ordering Process Works
We make it easy to coordinate your building schedules with the delivery of your windows and doors. Because cavity formers are needed on-site long before your handmade timber frames are finished, we have designed a simple, stress-free process to keep your project moving smoothly.
- Send Us Your Architectural Drawings
Share your building plans and architectural drawings with us. Our team will review the measurements to determine the exact sizes and cavity depths needed for your specific wall structures.
- Custom manufacturing
Once you approve the details, we produce your specialised cavity formers. We build them to the exact dimensions of your ordered Allwood timber windows and doors, ensuring a standardised, perfect fit.
- Early Site Delivery
We deliver the completed formers directly to your building site before your bricklayers start.This means your building team has the rigid templates ready the moment they begin laying the walls.
- Brickwork Construction
Your builders install the formers directly into the wall gaps, laying the bricks and blocks tightly around them. This creates a beautifully straight, square opening that stays permanently insulated.
- Flawless Joinery Fitting
While the walls are going up, we finish crafting your premium timber windows and doors. When they arrive on-site, they slide straight into the prepared openings with absolute precision, giving you a beautiful, airtight finish.
Why Choose Allwood Cavity Formers?
When you buy beautiful, handmade timber windows and doors from Allwood, you want the walls around them to be built to the same high standard. Our cavity formers are strong, high-specification frames designed to protect your home and make your build easier.
- Better Insulation: Cheap alternatives often let the cold sneak in. Our formers use high-density insulation to completely block out cold spots, keeping your rooms warm and helping you pass building regulations easily.
- Made for Strong Timber: Premium timber windows are heavy and solid. Our formers are made from heavy-duty materials that will not twist, bend, or crush, giving your new glazing a perfectly stable, rigid frame to sit in.
- Zero Measuring Mistakes: Buying parts from different places often leads to errors on site. Because we manage your entire window and former package together, we guarantee a flawless fit down to the final millimetre.
Frequently Asked Questions
Cavity formers are used to establish accurate openings for windows and doors while the walls are being built. They act as a physical template, helping builders maintain the correct size and shape so that the final timber windows and doors can be installed cleanly and accurately later on.
Yes, they can be used across a wide variety of construction types, including traditional brick-and-block masonry and timber-frame structures. They are commonly used in new build homes, domestic extensions, and commercial developments.
Yes. By providing bricklayers with a rigid guide to build against, cavity formers ensure the structural opening is square and true. This reduces the risk of alignment errors, making the eventual installation of your windows and doors much more straightforward.
Most modern cavity formers feature an integrated, insulated core that serves as a cavity closer. This insulation fills the gap between the inner and outer walls, which helps eliminate thermal bridging (cold paths), reduces draughts, and protects against internal dampness and mould.
Yes. Because the cavity former sets an exact, dependable measurement for the opening from day one, you do not need to wait for the brickwork to finish before ordering your windows and doors. They can be manufactured simultaneously, helping to keep your project moving forward smoothly.
