EWI to eaves, flush with window head [Version ID #412]

Author details

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Detail summary

Detail of external wall insulation to eaves; where existing overhanging eaves meet the head of an new replacement window fitted into depth of new EWI. Detail for insulation of space above the existing soffit, up to the underside of new phenolic eaves insulation. Designed to deal with potential cold bridge at eaves; where loft or roof insulation meets cavity or other wall insulation. New EWI to join to overhanging eaves insulation directly above window.

Technical description

Section detail. EWI to eaves with large overhang, existing eaves flush with head of window, new phenolic foam insulation above to join to EWI. Window replacement with triple glazed window with new timber frame.

Suggested Installation Sequence:

Preparation of roof and loft space: Remove any existing loose material and prepare in accordance with manufacturer's requirements.

Any alterations to cabling, existing ventilation, drainage, and other fixtures affected by work to be agreed with contract administrator prior to work being undertaken. Prior to start on site inspect the form and condition of the roof internally and externally, especially any structural timbers; institute repairs and/ or additional works necessary to make the structure suitable to receive works.


  1. Roll back existing loft insulation to reveal junction between ceiling and roof. Remove any debris. Ensure gap between rafters is clear to either eaves board or 200mm beyond outer edge of wall (where no eaves board), whichever is the smaller.
  2. Glue battens to upper surface of the eaves insulation boards (RF06c) 100mm in from each edge. On leading edge of the slab taper batten thickness to minimise risk of obstruction on installation.
  3. Once glue has set, push slabs into the gap over the top of the sole plate up to the eaves board or 200mm past whichever is the smaller.
  4. Fill gaps below eaves insulation to inside of soffit board with flexible eaves insulation. (FAB EW06c).
  5. Fit new window and window boards in place of existing. Seal all gaps for air-tightness around window reveal internally and externally. test for air-tightness.

Reference Specification:

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.

Tiling work: Clay tiles to BS EN 1304/ concrete (non interlocking) to BS EN 490. All battens/counterbattens and ridge/hip fixing battens to be timber species to BS 5534, Clause 4.12.1. All fasteners to BS 1202 as appropriate to fastener type

Existing guttering to be replaced/reinstated to BS EN 607, and BS EN 1462, Kitemark certified, clauses 3–7 and National Annexes. Collection and distribution of rainwater: Complete, and without leakage or noise nuisance.

For all works to existing roofs refer to Approved document C (resistance to contaminants and moisture), with reference to Section 2, and section 6.

Reference should be made to Document H (drainage and waste disposal). Approved Document F (ventilation) should be referred to with regards to ventilation to existing roofs and over eaves ventilation. Document L1b should be referred when working on existing dwellings, with particular attention to sections 5 and 6 regarding material alterations. Document L2b should be referred to with existing buildings other than dwellings.


Care should be taken to ensure air-tightness. Seal all service penetrations through EWI and existing wall. Lap and tape all membranes around edges of EWI system.

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 window to BS 644 [GD01]

    Triple glazed Softwood window.

    • Thermal Performance (overall u-value): 0.79W/m2K.
    • Air-tight installation: Install windows to achieve maximum air-tightness, using appropriate air-tight tape and sealants at all junctions and potential air-leakage points. (expanding PU foam will not be sufficient to achieve adequate air-tightness).
    • Size: As opening.
    • Opening Pattern/ Configuration: As existing (unless otherwise stated on detail).
    • 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.

    Green Building Store: Tel:+44 (0)1484 461705.
    Web: http://www.greenbuildingstore.co.uk
    Product Reference: Eco-Contract Ultra Outward Opening Casement Windows.

  • External Wall Insulation (Woodfibre), rendered finish [EW01]

    Composite woodfibre board for use on solid and hard to treat cavity walls.

    • Insulation back board: UdiTherm SK.
    • Insulation top board: Diffutherm NF (T&G, renderable).
    • Thermal conductivity: 0.045W/m2K. GWP 0.
    • 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.
    • Fixing: Fixed mechanically to substrate in accordance with manufacturers recommendations.
    • Render/carrier: to manufacturers standard.
    • Render: Udi Perl
    • Decorative finish: tbc
    • System guarantee: 25 years - ECO compliant insurances and guarantees.
    • System Certification : ETAG

    Unger. Product Reference: UdiFRONT.

  • Insulation to Eaves (rigid) [RF06c]

    • Manufacturer: Contractor's choice.
    • Phenolic foam.
    • Size: 50mm thickness
    • Width: cut to suit rafters.
    • Length: 750mm PLUS distance to eaves board or 200mm (whichever smallest).
    • Thermal conductivity: 0.023W/m2k.
    • Installation: Continuous with roof insulation, no gaps, to avoid cold bridging. Friction fit between rafters from inside loft, being careful not to damage existing roof membrane or structure or block existing ventilation paths.

    Contractor's choice

  • Insulation to Eaves (Flexible) [RF06c]

    • Woodfibre offcuts from external wall insulation.
    • Installation: Insert into gaps between wall plate/top of wall and rigid insulation to ensure continuity and avoid air movement.

    Back to Earth: Tel: 01392 861763. Web: http://www.backtoearth.co.uk/
    Product: Diffutherm

  • Double/Single-sided air seal tape [DP09b/a]

    Tape for junctions critical to air-tightness.

    • Location: see detail drawings - generally critical junctions for air-tightness. Size: 60mm (Single sided)/ 85mm (double sided).
    • Accessories: ORCON F sealant and TESCON PRIMER RP (for use on rough/old surfaces to assist adhesion)

    Back to Earth: Tel: 01392 861763. Web: http://www.backtoearth.co.uk/
    Product reference: TESCON VANA/ TESCON PROFIL - 2 release tapes (single sided) \ Contega SL (double sided)

  • Breathable Membrane [RF06c]

    Roof underlay. Sealed to phenolic foam insulation and dressed to drainage point at the end of each run of guttering to allow water to exit construction.

    Green Building Store. Tel: 01484 461705. Email: info@greenbuilding store. Web: http://www.greenbuildingstore.co.uk
    Product Reference: Solitex Plus

  • Intelligent air and vapour control layer [RF05b]

    Intelligent breather membrane.
    Fixing: Laps And Edges: Sealed with vapour-tight adhesive tape. At floor and ceiling junctions ensure is appropriately sealed.

    OPTION 1.) Pro-clima.
    Reference: Intello membrane
    OPTION 2.): Knauf.
    Thermoshell Vapour Control layer.


  1. Admin - 2015-04-29 09:59:16

    DWG uploaded. General formatting changes.

  2. Admin - 2015-03-27 16:20:50

    Preview image and .pdf file updated.

  3. Admin - 2015-03-27 12:15:54 [Displayed version]

    Codes updated. Intelligent vapour layer added to parts list.

  4. Admin - 2015-03-23 14:42:25

    General formatting. Technical description updated, links added and installation sequence updated. Parts list amended and codes added. Links to suppliers added.

  5. Admin - 2015-03-23 14:38:26

    General formatting. Technical description updated, links added and installation sequence updated. Parts list amended and codes added. Links to suppliers added.

  6. Admin - 2015-03-12 15:22:19

    Version 6. Triple glazed windows updated with FAB code

  7. Admin - 2015-03-12 15:21:20

    Intro/summary updated, technical description updated and expanded. BS and Approved doc information added. Parts list added.

  8. Admin - 2015-03-03 15:02:42

    Parts list added. Preview image updated.

  9. Admin - 2015-02-27 12:20:29

    Version 2- Title and .dwg file updated

  10. Admin - 2015-02-26 15:25:46

    Second version - Example image uploaded

  11. Admin - 2015-02-26 15:24:04

    First Version

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