EWI to slate roof verge with existing overhang

Author details

Original Author:Admin Organisation:Retrofit Pattern Book

Detail summary

Detail for EWI up to an existing overhanging verge with sufficient overhang to take depth of EWI. Installation of a new timber fascia board over EWI at junction with roof. Mastic seal at all edges, existing membrane below eaves to be re-dressed over insulation.

Technical description

Section Detail. EWI to Verge, existing overhanging. 200mm depth woodfibre insulation or less. Existing roof and membranes to remain. No change/alteration to existing excluding addition of new fascia board.

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 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.

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.

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

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

  • 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


  1. Admin - 2015-04-29 14:44:46 [Displayed version]

    DWG file uploaded. PArts list amendments.

  2. Admin - 2015-03-27 16:57:56

    Preview image and .pdf file updated.

  3. Admin - 2015-03-24 17:34:09

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

  4. Admin - 2015-03-24 17:32:28

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

  5. Admin - 2015-03-13 15:31:21

    Technical description updated. Parts list updated.

  6. Admin - 2015-03-06 12:53:49

    Parts list updated.

  7. Admin - 2015-03-06 12:29:11

    Version 1

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