Thermal Cavity Closers


The G240 cavity closer suits standard vertical cavity and sill details providing a thermal break to the cavity and an effective vertical DPC barrier.

  • Description & Key Features

    Product Description

    The G240 Cavity Closer has a double flange feature for use in standard in-line cavity wall details. It is also used in sill details by simply cutting a length to suit the width of the window and placed in the cavity at the sill. A DPC is still recommended in horizontal applications.

    The lightweight closers are available in sizes to suit all cavity widths and are simply installed, requiring no special tools. Lengths can be simply cut with a saw, with no loss of thermal efficiency, and with some specific products, PVC flanges provide a secure method of fixing.

    The closer can be used in individual lengths, or some may be preformed into frames or fixed directly on to window and door frames.

    G245 and G246 Plastic Fixing Clips enable the closer to be mortared securely to the brickwork. They also allow shorter lengths of closer to be joined together, thus reducing wastage.

    The Manthorpe G240 Cavity Closer can be used around timber doors and windows. When tested as a whole detail including timber window/door frames and plasterboard, it can be used as a part of a detail to satisfy the requirements of a cavity barrier as described in Part B of the building regulations.

    The cavity closer is non-load bearing and should not be used as replacement for traditional methods of fixing window and door frames to the masonry.

    Key Features

    • Lengths easily joined together without loss of thermal efficiency
    • Double flange feature
    • Insulation providing GWP rating of less than 5
    • Exceptionally secure
    • Available in varying cavity widths
  • Technical

    Fitting Requirements

    Brick up to sill height, cut and fit the sill closer. Cut the jamb lengths 75mm oversize and trim the flanges back to allow them to overlap the sill closer once fitted.

    Continue to brick up the wall, using the fixing clips to tie the closer into the masonry leaves as you go.

    In refurbishment situations, the closer can be screwed and plugged into the masonry through the fixing holes provided.


    Manthorpe Thermal Cavity Closers - BBA Certificate - 96-3226.pdf

    Regulations & Standards

    BS 5250:2011 Control of condensation in buildings.

    Approved Document L1 & L2:
    Conservation of fuel and power.

    NHBC Technical Guidance 6.7:
    Doors, Windows & Glazing

    BRE Digest Report 262: Thermal Insulation: Avoiding Risks.

    BRE Information Paper IP 1/06: Thermal Bridging at Junctions & Openings

  • Specifications

    Size Information

    Length 2.5m

    Cavity width from 50mm to 150mm

    Wider cavity sizes are available to order as specials up to 350mm.


    Extrusion: UPVC

    Styrofoam: CFC free


    Extrusion: White

    Styrofoam: Black

    Quantity Information

    6 lengths per pack