Cavity Formers
Precision Cavity Formersfor Openings That Needa Clean, Consistent Detail
A repeatable, accurate opening detail saves rework at glazing stage, and rework at glazing stage is the most expensive kind, because it happens last.
Manufactured in-house · supplied factory-direct
- Manufactured in our own factory
- Installed by our own teams
- Made to measure, never off the shelf
- FENSA-certified installation
The service
What this covers andwhen it is the right call
What the service covers
We supply cavity formers used to create accurate, consistent openings in cavity wall construction: components that define the reveal, close the cavity and give the following trades a square, predictable opening to work into.
Who it is for
Builders, contractors, developers and self-builders working across London who want the openings on a job to come out the same size, square and ready for glazing, rather than varying plot by plot or bricklayer by bricklayer.
When it is needed
At the point openings are formed in cavity walls, new build, extensions, structural alterations and knock-throughs. The specification decision is made before the wall goes up, because that is the only point at which it is cheap.
Why the detail matters
Every millimetre of variation at opening stage is paid for later: in packers, in oversized trims, in remedial sealing, or in a glazing unit that has to be remade. A consistent former gives an opening the glazing package can be manufactured against with confidence.
What it costs to wait
The problem does notstay the same size
Openings are formed early and glazed late, so mistakes stay hidden until the most expensive moment.
Openings that vary across a site
When each opening is set out by hand, no two plots match. The glazing schedule then needs individual survey and individual manufacture where it should have been repeatable.
Out-of-square reveals
A reveal that is not square shows up in the finished internal detail and forces the installer to choose between a level frame and an even margin.
Cold bridging and condensation at the reveal
A poorly closed cavity at the opening is a thermal weak point. It appears as cold reveals and condensation once the building is occupied and heated.
The common mistake: resolving the detail on site
Improvised closing and packing at opening stage is invisible until the glazing arrives, at which point the programme has no slack left to absorb it.
Our process
Five stages, one company,no handovers in between
Review the drawings and openings
We look at the opening schedule, the wall build-up and the intended glazing to establish what the former has to achieve.
Specification and confirmation
Sizes, quantities and details are confirmed in writing against the schedule before anything is produced.
Manufacture and supply
Components are produced to the agreed specification on our own production line, factory-direct with no distributor in between.
Scheduled delivery to site
Deliveries are scheduled against your build programme so components arrive when the openings are being formed, not weeks either side.
Glazing to the formed openings
Where we are also supplying the windows and doors, the units are surveyed to the formed openings and manufactured to that survey.
What you get
Specific outcomes,not general assurances
Repeatable openings across a site
Consistent formers mean consistent openings, which makes the glazing package repeatable rather than bespoke plot by plot.
Less rework at glazing stage
Square, accurate openings reduce packing, oversized trims and remedial sealing at the end of the programme.
A cleaner reveal detail
The finished internal reveal is defined by the former rather than by however the opening was closed on the day.
Programme protection
Scheduled delivery keeps the opening-forming stage moving instead of waiting on a merchant's stock.
Factory-direct pricing
You are buying from the manufacturer, with no distributor margin added between the factory and the site.
One supplier through to glazing
Where we also supply the windows and doors, the opening detail and the glazing are specified together.
In detail
Materials, methods andthe situations they suit
What a cavity former does
In cavity wall construction, an opening has to be formed, the cavity has to be closed, and the reveal has to be defined for the frame that will eventually sit in it. Doing this with a manufactured component instead of an improvised arrangement gives a straight, square, dimensionally predictable opening.
That predictability is the whole value: the glazing package can be manufactured against known dimensions, and the following trades work into a detail that is the same in every opening.
Thermal and moisture considerations
The junction between the frame and the wall is a recognised weak point for heat loss and for moisture. Closing the cavity properly at the opening reduces cold bridging, which reduces the risk of cold internal reveals and the surface condensation and mould that follow.
Moisture management matters equally: the detail has to keep water crossing the cavity out of the inner leaf, and it has to keep working after the frame is installed and sealed.
Coordinating formers with the glazing package
The most efficient sequence is to specify the opening detail and the glazing together. When the same manufacturer supplies both, the tolerance the frame needs is designed into the opening rather than discovered later.
Where we also install, our surveyor measures the formed openings before manufacture, so even where site variation exists, the units are made to what was built.
New build, extension and refurbishment
On new build and multi-plot developments the benefit is repeatability across many identical openings. On single extensions the benefit is a clean detail at the one or two openings that will define how the finished room looks.
In refurbishment, forming a new opening in an existing cavity wall introduces its own conditions, existing wall build-up, structural support and the state of the cavity, which are assessed against the drawings before specification.
Supply to trade across London
Trade supply is a core part of the business. Builders, contractors and developers get factory-direct pricing and deliveries scheduled against the build programme rather than a merchant's stock position.
Because we also manufacture windows and doors, a site can take the opening components and the glazing package from one supplier, on one schedule, with one point of contact.
Straight answers
Questions we are askedabout cavity formers
- What do cavity formers cost?
- Pricing depends on sizes and quantities and is quoted against your opening schedule. Supply is factory-direct, so there is no distributor margin in the figure.
- What lead time should I allow?
- We confirm a production and delivery date in writing against your programme once the schedule is agreed.
- Can you deliver to a live site?
- Yes, deliveries are scheduled with the site manager so components arrive when the openings are being formed.
- Do you supply formers without the glazing?
- Yes, as a supply-only trade order. Many sites take both, but the components can be supplied on their own.
- Will this help with cold bridging at the reveal?
- A properly closed cavity at the opening is one of the recognised measures for reducing heat loss and cold reveals at the frame junction.
- Can you work from architect's drawings?
- Yes. We review the opening schedule and wall build-up and confirm the specification in writing before manufacture.
- Do you supply to developers running multiple plots?
- Yes, repeatable openings across plots is one of the main reasons developers use manufactured formers.
- Can the same order include windows and doors?
- It can, and it is the most efficient way to run it: one supplier, one schedule, opening detail and glazing specified together.
- Do you cover sites outside South West London?
- Trade supply and scheduled deliveries cover builders, contractors and developers working across London.
- Who measures the openings for the glazing?
- Where we install, we survey the formed openings ourselves before manufacture. On supply-only orders, measurement responsibility is agreed in writing up front.
Related services
Where we work
Cavity Formers supplied and installed across South West London and the surrounding postcodes.
Next step
Send us your opening scheduleand we will price it
Give us the drawings and the programme. We will confirm specification, quantities and delivery dates in writing before production starts.
- Manufactured in our own factory, then installed by our own teams
- FENSA-certified installation on qualifying replacement work
- Office open Mon – Fri, 8am – 4pm
Tell us about your project
One short form. We will confirm the next step by phone or email.
We reply during opening hours: Mon – Fri, 8am – 4pm. Prefer to talk? Call 01483 968616.