EWI Service duct within Insulation - Stepped face

Author details

Original Author:Admin Organisation:Retrofit Pattern Book

Detail summary

A detail for an insulated services run within an external wall insulation system, stepped in from the finished face of the wall. Used where service runs such as soil pipes or ventilation ducts are to be contained within the depth of the insulation, meaning an accessible service void should be created.

Prior to work carry out a visual inspection of the services to be enclosed within service void, to ensure in sound condition before constructing service void.

Technical description

Plan detail. EWI. Service duct detail, stepped face. recessed original pipework.

Reference Specification:

Fibreboard specification:

  • Hardboard: To BS EN 622-2.
  • Medium board: To BS EN 622-3.
  • Dry processed boards (Medium density fibre board): To BS EN 622-5.
  • Particleboards: To BS EN 312.


  • Appearance class, hardwood: To BS EN 635-2.
  • Appearance class, softwood: To BS EN 635-3.
  • Bond quality: To BS EN 314-2.

Plastics veneered board: To BS 4965.

  • Laminate grade: VG.


Care should be taken to ensure air-tightness. Seal all service penetrations. Lap and tape all membranes.

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: 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

  • Woodfibre External Wall insulation system [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/

  • Hardwood trim to edge of panel

    • Manufacturer: Contractors choice.
    • Type: as drawing
    • Finished size: as drawing.
    • Species: as drawing.
    • Class: Class 1 to BS 1186-3.
    • Preservative treatment: Boron as section Z12 and WPA Commodity Specification C10, service life 30 years.
    • Finish as delivered: Natural
    • Fixing: Countersunk screws and 400mm centres.
    • Certification: all timber to be FSC certified.

    Contractor's choice.

  • Treated softwood studding [EW03b]

    • Strength class: C16
    • Species: Contractors choice.
    • Size: as detail/ to suit depth of insulation.
    • Stud centres: As detail/to suit services to be boxed in.
    • Fasteners: Framing anchor.

    Contractor's choice.

  • Flexible woodfibre insulation to service void [EW03b]

    Woodfibre insulation, loose or batts, to provide insulation between new service runs to ensure continuous thermal envelope.

    • GWP: 0
    • Thickness: to full depth of insulation.
    • Installation: Friction fit between services to avoid thermal bypass and ensure high thermal performance.

    Unger-Diffutherm. Product Reference:Reference: UdiFLEX
    Supplied by: Back To Earth.
    Tel: 01392 861763
    Web: http://www.backtoearth.co.uk/

  • Render carrier board (to form access panel) [EW03b]

    GTEC render board. To form removable panel for access to existing pipework. Screw fixed to timber frame. Rendered over to match adjacent EWI.

    • Render board: Lafarge / Siniat. Product Reference: Aqua board
    • Render: As EWI manufacturers recommendations.
  • Insulation to access panel [EW03b]

    External insulation wall board. 50mm nominal thickness (to suit void depth). Adhesive fix to rear of render carrier board.

    Kingspan Insulation Ltd. Product reference: Kooltherm K5 External Wall Board.

  • EWI Accessories [EW01]

    Render Stop bead for adjacent EWI render to hardwood trim.

    As EWI manufacturers recommendations.


  1. Admin - 2015-04-30 12:03:56 [Displayed version]

    Formatting revisions. Preview image uploaded.

  2. Admin - 2015-04-30 12:03:12

    New detail created. Version 1.

  3. Admin - 2015-04-30 12:02:44

    New detail created. Version 1.

  4. Admin - 2015-04-30 12:00:08

    New detail created. Version 1.

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