New window to EWI, for single brick reveal (section) [Version ID #214]

Author details

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Detail summary

New window fitted into EWI with a timber frame for mounting of window into external wall insulation. Used where single brick reveal means original window was originally sat behind and larger than structural opening in outer face of existing masonry wall.

This detail is designed to reduce thermal bridging and improve air-tightness whilst spreading structural load of new window and maximising glazed area. The timber box also acts as self-finished internal reveal. (May be painted/ varnished as required).

Technical description

Section detail. EWI to new replacement window, on box into former window location. New triple glazed window to replace existing. SUGGESTED INSTALLATION SEQUENCE:

Windows and window boxes should be fitted prior to installation of external wall insulation wherever possible. Ideally installed from outside, with insulation fitted tight up to box and appropriate air-tightness work undertaken as shown on detail drawings. Where this is not possible, windows and boxes can be fitted from inside, with temporary boxing acting as place-holder within the insulation until installation can take place.


All new replacement timber windows to BS 644, operation and strength characteristics to BS 6375-2. All timber members in windows to BS EN 942. Glazing beads clear finish to Class J2.

Care should be taken during the installation to ensure the continuity of insulation and air-tightness at the junction between window, existing wall and external wall insulation.

All insulation to be continuous to avoid thermal bridging.

Preparation of external wall: Remove any existing loose material and prepare in accordance with manufacturer's requirements.

Any alterations to drainage and other fixtures, or work to prepare the substrate, to be agreed with contract administrator prior to work being undertaken. Prior to start on site inspect the form and condition of the structural substrate; institute repairs and/ or additional works necessary to make the substrate suitable to receive EWI system.

Parts list

  • New Timber frame, triple-glazed windows [GD01]

    Eco-Contract Ultra Outward Opening Casement Windows.\ Thermal Performance (overall u-value) : 0.79W/m2K.\ Air-tight. Size: As schematic.\ Opening Pattern/ Configuration : As existing (unless otherwise stated on schematic).\ Sash/Frame Material: FSC 100% Redwood.\ Drip Rail : Aluminium. \ Finish - Interior: Factory finished paint/varnish system.\ Finish - Exterior: Factory finished paint/varnish system. \ Glazing Unit : Triple, Argon Fill, 44mm. \ Glazing Type: as standard triple glazed unless stated: Light transmission : 72%. \ Solar factor (g): 52%. \ Handle Type: Manufacturer's standard, factory fitted. \ Security: Secured by Design.\ Accessories: Egress Hinges and Child Safety Restrictors. \ Guarantees: Manufacturer's standard.

    Manufacturer: Green Building Store. \ \ Tel: +44 (0)1484 461705. \ Reference: Eco-Contract Ultra Outward Opening Casement Windows

  • EWI (Woodfibre) System With Rendered Finish [EW01]

    For use on solid and hard to treat cavity walls. Composite woodfibre board. UdiTherm SK back board, Diffutherm NF (T&G, renderable) top board. \ Fixed mechanically to substrate in accordance with manufacturers recommendations. \ Base Coat - levelling on substrate: 90% contact required around edge of boards between board and substrate to prevent thermal bypass. If substrate is very uneven, use base-coat material around edge of board to achieve contact. \ Thermal conductivity: 0.045W/m2K. GWP 0.

    Unger \ \ Reference: UdiFRONT. \ Render: UDI Perl

  • Self-finished softwood box to mount into EWI [EW04a]

    To fit existing structural opening. Box to be constructed to same outside dimension as window opening. Window box depth as detail drawing. \ Inner edge of reveal to protrude 20mm inside the room, beyond the existing plaster face. \ Species: European Redwood. \ Section Sizes: As detail drawing. \ Adhesive to contractor’s specification. Mechanically pre-fixed and glued to window frame to existing masonry : Window reveals to be fixed back to outer leaf of masonry with frame fixings countersunk and plugged, at between 450mm - 600mm centres to suit window size. Also fixed back to timber studwork on inner face of wall- located in position of original sash box - and so spreading load of new window across the wall.\ Certification: All timber to be FSC certified.

    Contractors choice

  • Single-sided air seal tape [DP09a/]

    Tape for junctions critical to air-tightness. 60mm (typical). \ Accessories: ORCON F sealant and TESCON PRIMER RP (for use on rough/old surfaces to assist adhesion)

    Pro Clima \ \ TESCON VANA/ TESCON PROFIL (2 release tapes)

  • External Extended Cill [EW01]

    Replacement aluminium cill

    Manufacturer: Green Building Store. \ or as window manufacturer \ \ Tel: +44 (0)1484 461705. \ Reference: Manufacturer's standard - aluminimum

  • M20a Repairing Plaster [EW04a]

    To replace defective plaster removed or damaged during window installation. \ Remove existing plaster and finish before installing new plaster. \ Finish as existing.

    Contractors choice.


  1. Admin - 2015-04-29 15:32:52

    DWG file updated. General amendments to formatting.

  2. Admin - 2015-03-27 17:40:34

    Preview image and .pdf file updated.

  3. Admin - 2015-03-25 12:37:08

    General re-formatting. Introduction text revised. Technical description updated with links to approved docs and additional specification notes. Parts list updated with suppliers links.

  4. Admin - 2015-03-13 16:57:26

    Errors removed. Parts list updated with Compac foam.

  5. Admin - 2015-03-13 16:56:38

    Errors removed

  6. Admin - 2015-03-13 16:49:34 [Displayed version]

    Technical description updated. Parts list updated.

  7. Admin - 2015-03-10 10:19:40

    Version 2 - title update

  8. Admin - 2015-03-10 10:18:14

    First version

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