BigBlok Cavity Closer


With larger cavities being specified across new-build properties in order to meet stringent thermal efficiency regulations, BigBlok is meeting the demand for a simple slot-together system that quickly and cost-effectively closes off window and door openings of any size in any type of wall. Making it an essential component for low U-value construction, helping to achieve higher ratings in the Code for Sustainable Homes.

Features and benefits:

  • Creates rigid bricklaying template and seals walls with cavities up to 300 mm, helping in meeting stringent thermal efficiency regulations.
  • Manufactured from 100% post-consumer recycled UPVC – delivering a sustainable solution.
  • Closes opening with continuous CFC/HCFC-free insulation – reducing U-values to prevent thermal bridging.
  • Quick and easy to fabricate and fit, with straight cuts and slot-together fitting
  • Compatible with UPVC, timber, steel and composite doors and windows
  • Tough and robust to withstand demanding site conditions
  • Extensive range of fitting options to suit every building project


  • Meets Accredited Construction Details.
  • Meets Part L of Building Regulations.

General information

Uniclass 2015

Pr_35_90_50_64 Plastics cavity closersPrimary


F30/18 Cavity closers

F30/180 Cavity closers

Specification data - Plastics cavity closers

Product Reference

BigBlok Cavity closer

Cavity width

125 mm

140 mm

150 mm

170 mm

200 mm

250 mm

300 mm


Not required

Quick fit window retainer

Thermal barrier

Cavalok corners