EWI to pitched roof, extended verge (existing roof supported)

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. Designed to retain the character of the existing verge. In this case,where a pitched roof needs to be extends beyond 200mm to provide enough shelter for insulation. New fascia board fixed to front face of EWI to match existing.

Technical description

Section detail. EWI verge detail, with extended slates. 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, to be agreed with contract administrator prior to work being undertaken. Prior to start on site inspect: form and condition of the existing 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.

Parts list

  • EWI (Woodfibre) System, 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. Product Reference: UdiFRONT.

  • Breather Membrane/ Roof-underlay [RF06c]

    Roof underlay. Installation: Sealed to insulation to eaves 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.
    Web: http://www.greenbuildingstore.co.uk
    Product Reference: Solitex Plus

  • Softwood Eaves Fascia Board [RF09b]

    • Species:European White wood to appearance class BS EN 942, clas J30.
    • Size: to suit existing.
    • Treatment: required.
    • Fasteners: Stainless steel nails at fixing centres determined by contractor.

    Contractor's choice.

  • Softwood battens [RF06a]

    • Size: as drawn. ,li>Grading: Fully factory pre-graded.
    • Preservative treatment required: contractor's choice.
    • Fasteners: Glue fixings.
    • Certification: All timber to be FSc certified (or reused where possible)

    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 14:23:16 [Displayed version]

    Title amendment. Technical description amended to remove notes on soil pipes and existing gas meters. DWG file uploaded.

  2. Admin - 2015-03-27 16:56:42

    Preview image and .pdf file updated.

  3. Admin - 2015-03-24 17:32:26

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

  4. Admin - 2015-03-13 15:27:02

    Parts list updated. technical description expanded with BS EN detail and approved docs.

  5. Admin - 2015-03-06 12:25:55

    Technical description updated

  6. Admin - 2015-03-05 15:28:36

    Title update

  7. Admin - 2015-03-05 15:27:58

    First version

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