Cavity Closers

Why do I need to consider a cavity closer?

When a cavity isn’t correctly closed around the window, water ingress is likely to occur, over a short period of time; damp and mould will seep around the frame. Most homeowners are sure to blame the window as they cannot see the cavity closer from within the house, even the best-constructed windows will receive this criticism if the cavity isn’t efficiently closed.

In compliance with Building Regulations Part C, cavity closers surrounding both doors and windows are necessary for the prevention of water penetration. The window frame requires a minimum set back of 30mm within the cavity, it will then need sealing around the frame. For further efficiency and prevention of water ingress, ensure there are ridges on the cavity closer you use.

However, water penetration is only one of the contributing reasons. Heat loss and the entrance of cold draughts are another concept that draws the attention of home-buyers and builders. Building Regulation Part L recognizes issues of cold bridging, this is the state at which a building has a heat transfer that is significantly higher than that of the materials of the surroundings. Insulated closers overcome heat loss that takes place around the cavities. Failing to insulate the closing may cause problems of mould growth, staining and condensation. This will likely cause deterioration of the paintwork and internal plaster after a prolonged period.

Fire rated cavity closers can be used in order to comply with Building Regulation Part B. This closer can prevent the spreading of fire for up to one hour. Insulated cavity closer without fire rating will not comply with regulations.

Sustainability is a huge factor in every building project as recognized in Building Regulation Part L The regulation here states that the cavity closers’ thermal resistance path has to be a minimum of 0.45m2k/W. The higher this number the less heat loss.

Which cavity closer should I be using?

There are a number of questions you will need to ask yourself when selecting the closers needed for your project.

1. Is this a new project or are the windows being replaced?

For new projects you will need a 1st fix product, when replacing windows a product of 2nd fix should be selected.

2. What is the size of the cavity?

Very simply, if the space between the brick and block, the cavity width, is 60mm you will require a 60mm wide closer.

3. Will you comply with the Building Regulations?

There are 3 parts of regulations you need to comply with; B, C and L. To comply with all three, choose a fire rated closer that will provide sufficient cavity insulation, ensure the thermal resistance path is a minimum of the R-Value which is 0.45m2k/W.

Would you like an easier, quicker and more cost-effective cavity closer solution?

Allform is your solution; bespoke, pre-formed, insulated cavity closers prepared to your exact requirements. Cavity sizes can vary from 70 to 130mm and we make them all. Window formers can be constructed within 48 hours from sign-off and delivered direct to your site*. Our window formers are made from a solid white plastic section, with internal insulation and a keyed plastic face making it easy to plaster to.

Each window former frame has a corner support strut, 2 if the former is wider than 1.5mtrs. They also have a wooden brace holding both sides together, but if the window former is higher than 1.5mtrs then a 2nd brace is fitted for stability. Each corner joint is screwed with double fixing.


*subject to stock availability & workload