EWI to pitched roof with extended verge

Author details

Original Author:Admin Organisation:Retrofit Pattern Book

Detail summary

Detail for external wall insulation to the underside of a pitched slate roof with an extended verge. Used to retain the character of the existing pitched roof and verge after installing EWI system. Where the existing pitched roof does not cover the additional depth of the EWI the existing roof is subsequently extended over the new insulation.

Technical description

Section detail. EWI verge detail, with extended slates, supported from existing roof. Slate roof.

Reference Specification:

Natural slates to BS EN 12326-1 and -2. Battens, counterbattens and ridge/ hip fixing battens Timber species: To BS 5534, clause 4.12.1. Fasteners to BS 1202. All breathable membranes under Slating to be Agrément certified. Bitumen sheet to BS8747 Annex B.

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

Existing services

Rainwater Pipes and Waste Water Drainage: Rainwater pipes and waste water pipes will be moved to the outer face of insulation as standard, and swan-necked back into gulleys where possible. Any work additional to this should be agreed in writing with the contract administrator.

Where windows are to be replaced in insulation please refer to contract/window schedules for details. Where windows are to be retained in insulation please refer to relevant detail drawings to show reveal insulation and cills.

Parts list

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

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

    • Insulation back board: 100mm UdiTherm SK.
    • Insulation top board: 100mm 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/

  • Breathable Membrane [RF06a]

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

    • Manufacturer: DuPont Tyvek
    • Roll Size: Contractor's choice.
    • Installation: Lapped and taped to existing membrane. New membrane over top edge of EWI edge tape sealed. Render over.
    • Accessories: Tyvek 2060B Tape.

    DuPont Tyvek.
    Product Reference: Tyvek Supro

  • Softwood battens [RF06a]

    To maintain air path.

    • Size as required on site/ as existing.
    • Grading: Fully factory pre-graded.
    • Preservative treatment required- contractor's choice.
    • Fasteners: Glued
    • Certification: All timber to be FSc certified (or reused from existing on site.)

    Contractor's choice.

  • Tiles and battens to match existing.

    • Natural slates to BS EN 12326-1 and -2.
    • Battens, counterbattens and ridge/ hip fixing battens:
    • Timber species: To BS 5534, clause 4.12.1.
    • Fasteners to BS 1202.

    Contractor's choice.


  1. Admin - 2015-04-29 14:25:55 [Displayed version]

    Technical description amended to remove references to soil pipes and doors.

  2. Admin - 2015-04-29 14:19:59

    DWG file updated. General formatting amendments.

  3. Admin - 2015-03-27 16:54:55

    Preview image and .pdf file updated.

  4. Admin - 2015-03-27 14:37:06

    Minor changes to remove errors.

  5. Admin - 2015-03-24 17:32:25

    General formatting. Technical description expanded with additional clauses and approved document links. Parts list updated with suppliers links. Tile and battens added parts list.

  6. Admin - 2015-03-13 14:52:13

    Parts list added. Technical description updated.

  7. Admin - 2015-03-05 15:26:54

    Title update. Category update.

  8. Admin - 2015-03-05 15:24:04

    Version 3: Category change

  9. Admin - 2015-03-05 15:23:26

    Title uodated

  10. Admin - 2015-03-05 14:08:27

    First version

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