EWI to Flush Flat Roof with Gutter

Author details

Original Author:Admin Organisation:Retrofit Pattern Book

Detail summary

Detail for external wall insulation up an existing external wall, up to an existing flat roof where no additional insulation is to be added to the existing roof buildup. To finish the EWI and address water run-off: a single piece stainless steel gutter is provided to cap the new EWI; and a new membrane lapped from the existing roof over the top of the EWI beneath the rendered finish.

Technical description

Section detail, EWI to flat roof with gutter (to be replaced). No insulation work to existing roof.

Suggested Installation Sequence:

  1. Fix EWI to wall over existing fascia board.
  2. Install breathable roofing membrane above.
  3. Fix gutter above, under existing roofing membrane; taking care to ensure continuity with existing roofing membrane.
  4. Lap existing roofing membrane into gutter and make water-tight.

Reference Specification:

All guttering to BS EN 12056-3, 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). 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 existing roof, to be agreed with contract administrator prior to work being undertaken. Prior to start on site inspect the form and condition of the roof structure; institute repairs and/ or additional works necessary to make the roof edge suitable to receive EWI system.

Parts list

  • Stainless Steel box Gutter [RF06g]

    Flashing at junction between flat roof verge and external wall insulation. To BS 460, and BS EN 12056-3, clauses 3–7 and National Annexes.

    • Manufacturer: Contractor's choice.
    • Profile: As drawing.
    • Gauge: 1.2mm min.
    • Jointing: Joints to be avoided where possible. If required must be fully welded and tested. Could be glued and blind riveted subject to approval.
    • Size: Contractor's choice- to suit existing roof dimensions and cover depth of external wall insulation. Ensure provides adequate capacity for rainwater discharge from roof.
    • Finish as delivered: Self finished Stainless Steel grade 304.
    • Setting out: To falls.
    • Fasteners: as manufacturers recommendations.
    • Accessories: As welded stop ends.
    • Testing: Test on completion.

    Contractor's choice

  • EWI (Woodfibre) System With 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/

  • Airtightness works to ceiling [DP03]

    Seal all ceilings and repair any cracks in plaster to ensure no air-leaks.

    • Location: All ceilings
    • Product: Standard decorators caulk

    Contractor's choice.

  • Breather Membrane [RF06g]

    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

  • Gutter support clip and timber support

    Clip/ support to provide support for box gutter and provide fixing back to existing wall. Timber Batten to support gutter.

    Contractor's choice or to gutter manufacturers recommendation.

  • EWI (Woodfibre) accessories: Corner bead [EW01]

    Corner reinforcement for render support at corners and junctions with gutter

    As EWI manufacturers recommendations.


  1. Admin - 2015-04-29 10:16:17 [Displayed version]

    DWG file uploaded. General formatting changes. PDF file updated to latest revision

  2. Admin - 2015-04-29 10:14:49

    DWG file uploaded. General formatting changes.

  3. Admin - 2015-03-27 16:23:29

    Preview image and .pdf file updated.

  4. Admin - 2015-03-27 12:34:33

    General formatting. Gutter clip, bretaher membrane, and Air tightness works added to parts list.

  5. Admin - 2015-03-23 16:17:09

    General re-formatting.

  6. Admin - 2015-03-23 15:19:25

    General re-formatting. Technical description updated with installation sequence. Parts list updated with suppliers links.

  7. Admin - 2015-03-12 12:01:07

    Version 5. Parts list updated and errors removed.

  8. Admin - 2015-03-11 17:26:32

    Parts list updated with codes

  9. Admin - 2015-03-11 15:09:46

    Parts list added, technical description and intro updated.

  10. Admin - 2015-02-27 12:22:07

    Version 2- .dwg file updated

  11. Admin - 2015-02-26 16:01:55

    First version

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