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Providing a rigid bricklaying template, window acceptor, damp-proof course and thermal break all-in-one, the PVC-U Cavalok cavity closure range is designed to create window and door openings while sealing cavities between 50mm and 300mm wide. In addition, its built-in insulation delivers enhanced thermal efficiency and it's also manufactured entirely from post-consumer recycled PVC-U. Fire-rated cavity closers can also act as a barrier to enhance fire protection in your buildings.
Choose the right cavity closer for your project

Nationwide Windows offers a range of cavity closer products to fit cavities from 50mm to 300mm wide, catering for every type of building:

  • Cavalok cavity closer – insulated closer for 50mm-100mm cavity walls
  • FlameBlok – combined fire barrier and insulated cavity closer
  • BigBlok – insulated cavity closer for buildings with wider cavities, from 125mm to 300mm wide
cavity closers

Cavalok 50mm to 100mm Cavity Closers

The Cavalok cavity closure system is designed to create window and door openings while sealing cavities between 50mm and 100mm wide. The simple slot together system is easy to fit and fully compatible will all types of building, whether masonry, steel or timber-framed, and with PVC-U, wood, metal and composite windows and doors. With built-in insulation, the closer delivers enhanced thermal efficiency to meet current Building Regulations. It's also manufactured entirely from post-consumer recycled PVC-U for a complete sustainable solution, the system is also fully NHBC and BBA approved and complies with Building Regulations and ACDs.

thermal inserts

Cavalok BigBlok: 125mm to 300mm Cavity Closers

BigBlok cavity closers have been developed to meet the demand for closures in buildings with cavities from 125mm to 300mm wide. Larger cavities that can accommodate more insulation are increasingly being specified on new-build properties to meet stringent thermal efficiency regulations and the requirements of the Code for Sustainable Homes. BigBlok's solid block of insulation is ideal for low U-Value construction and compatible with all PVC-U, timber, steel and composite door and window types, it prevents thermal bridging while providing an accurate brick laying template. Like it's smaller sister, all BigBlok cavity closers are manufactured entirely from post-consumer recycled PVC-U waste plastic, often diverted from landfill. The integral insulation within BigBlok cavity closers provides continuous thermal insulation around the opening. It has a Global Warming Potential (GWP) of less than five and an Ozone Depleting Potential (ODP) of zero – meeting the requirements of the Code for Sustainable Homes.

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The FlameBlok cavity closer is the first fully tested fire-rated cavity closer available for cavities greater than 100mm, and the only fire-rated closer manufactured entirely from post-consumer recycled PVC-U. Wall cavities are a hidden danger area for fires, so cavity fire barriers that help to prevent fires spreading are a critical consideration.

Independently tested fire protection for up to 90 minutes
FlameBlok cavity closers create a continuous ring of fire protection around openings in cavity walls, combing cavity closer and cavity fire barrier in one product. They feature foil-encased fire insulation that reflects flames and heat and prevents moisture penetration. FlameBlok cavity closers have been independently and rigorously tested to BSE EN 1363-1:1999 by Chiltern International Fire, achieving 90-minute integrity in masonry walls and 60-minute integrity in timber-framed walls. The new FlameBlok cavity closer not only complies with current Accredited Construction Details (ACDs), it also meets anticipated tougher new ACDs and Part L regulations on thermal performance, as well as exceeding current Part B requirements for fire barriers in non-masonry construction.