EWI to soffit eaves by room-in-roof

Author details

Original Author:Admin Organisation:Retrofit Pattern Book

Detail summary

Detail for external wall insulation up to existing soffit eaves, including new loft insulation to an existing room-in-roof. This detail is designed to prevent a potential cold bridge at eaves where the loft or roof insulation meets external wall insulation at a soffit deep enough to accommodate new EWI beneath it. Loft and external wall insulation to be installed from outside.

Technical description

Section detail. EWI to existing wall. Up to eaves soffit, with new phenolic foam insulation to join to EWI. Installed from outside.

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 the 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 substrate suitable to receive insulation.


  1. Lift bottom three/four rows of slates/tiles and associated battens as required. Roll back any existing roofing membrane.
  2. Insert rigid insulation piece between the rafters, leaving a minimum of 25mm between the top face and top side of rafter. Notch rigid insulation over sole plate to ensure no gap between top of ceiling and underside of rigid insulation.
  3. Fill gaps between the outer face of the sole plate, the top of the brickwork and the inside face of the external wall insulation to minimise air gaps within construction.
  4. Dress rigid insulation board against the inside face of the eaves fascia board.
  5. Glue battens to upper surface of the cut slabs 100mm in from each edge.
  6. Fit over fascia eaves ventilator.
  7. Re-fix roofing membrane and tape to new membrane. Re-fix existing battens and slates/tiles.

Reference Specification:

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 roof or eaves, to be agreed with contract administrator prior to work being undertaken. Prior to start on site inspect the form and condition of the roof and eaves structure; institute repairs and/ or additional works necessary to make the existing condition suitable to receive EWI system.

Parts list

  • EWI (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-Diffutherm. Product Reference: UdiFRONT.
    Supplied by: Back To Earth. Tel: 01392 861763
    Web: http://www.backtoearth.co.uk/

  • Insulation to Eaves (rigid) [RF06a]

    • Manufacturer: Contractor's choice.
    • Phenolic foam.
    • Size: 50mm thickness (25mm vent gap must be maintained)
    • Width: cut to suit rafters.
    • Length: 600mm minimum - to ensure overlap with loft/roof insulation and any wall insulation and avoid thermal bridge.
    • 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 Reference: Diffutherm

  • Breathable Membrane [RF06a]

    Flexible damp proofing sheet. To Packaging and Industrial Films Association (PIFA) Standard 6/83A, or Agrément certified.

    • Manufacturer: DuPont Tyvek
    • Roll Size: Contractor's choice.
    • Installation: Sealed to phenolic foam insulation and dressed to drainage point at the end of each run of guttering.
    • Accessories: Tyvek 2060B Tape.

    DuPont Tyvek.
    Product Reference: Tyvek Supro

  • 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)

  • Softwood battens (for replacment slating) [RF06c]

    • Size: 50x25mm timber battens.
    • Grading: Fully factory Pre-graded.
    • Preservative treatment: Required- contractor's choice.
    • Certification: All timber to be FSC certified \ Preservative treatment required.
    • Fastening: Galvanized steel nails, sized to penetrate 40 mm (minimum) into rafters.

    Contractor's choice.

  • Over fascia Eaves ventilator [RF06a]

    Ventilator strip to allow airflow under roof whilst preventing ingress of insects and small birds.

    Hambleside Danelaw Ltd: Tel:+44 (0) 1327 701 900.
    Email: sales@hambleside-danelaw.co.uk
    Web: http://www.hambleside-danelaw.co.uk
    Product Referance: HD12000U Universal Over Fascia Ventilator or equivalent.


  1. Admin - 2015-04-29 09:37:37 [Displayed version]

    DWG uploaded. Back To Earth added to contacts list for EW01.

  2. Admin - 2015-04-22 14:26:02

    Pdf file updated to match parts list codes

  3. Admin - 2015-03-27 16:18:26

    Preview image and .pdf file updated.

  4. Admin - 2015-03-27 11:30:53

    Codes updated, concurrent with drawing.

  5. Admin - 2015-03-23 16:02:27

    Parts list formatting

  6. Admin - 2015-03-23 13:06:44

    General formatting. Intro updated and expanded. Technical description updated with Approved doc links, and revised installation sequence. Parts list updated with codes and Links to suppliers/manufacturers.

  7. Admin - 2015-03-13 18:06:59

    Technical description updated. Suggested installation sequence added. Parts list updated.

  8. Admin - 2015-03-12 13:39:06

    Version 4. Title and intro summary updated. Technical description updated and expanded. BS and Approved doc information added. Parts list updated. Preview image and pdf file updated with revised linetype colours /line-weights

  9. Admin - 2015-03-03 12:19:17

    Parts list updated

  10. Admin - 2015-02-27 12:17:32

    Version 2 - .dwg file updated

  11. Admin - 2015-02-26 14:51:53

    First Version

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