Retained window to EWI, thin jamb (Plan)

Author details

Original Author:Admin Organisation:Retrofit Pattern Book

Detail summary

Detail for external wall insulation to an existing window to be retained, where the existing window sits up against the inside edge of existing window jamb. This detail proposes Aerogel insulation to be used where the existing window jamb and head is too narrow for standard 40mm woodfibre reveal boards.

Technical description

Plan detail. EWI to existing retained window, perpendicular cill profile.

Reference Specification

Where the existing position of windows is to be retained when EWI is installed, window reveals must be insulated to prevent cold bridge. Phenolic foam to be used in foam based EWI systems or in woodfibre systems where existing window jamb and head is too narrow for standard 40mm woodfibre reveal boards. All phenolic foam (PF): To BS EN 13166.


Care should be taken during the installation to ensure the continuity of insulation and air-tightness at the junction between window, existing wall and external wall insulation.

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 the 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

  • Aerogel matting [DP01b]

    Aerogel thermal insulation. Thermal conductivity 0.013 W/mK.

    Thermablok. Tel: 01622 840289

  • 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. Product Reference: UdiFRONT.

  • EWI (Woodfibre) accessories [EW01]

    • Adhesive Render Edging Strip to achieve air-tight seal around window.
    • Corner reinforcement strip.

    As EWI manufacturers recommendations.

  • Single-sided air seal tape [DP09a]

    Tape for junctions critical to air-tightness.

    • Location: see detail drawings - generally critical junctions for air-tightness. Size: 60mm (Single sided).
    • Accessories: ORCON F sealant and TESCON PRIMER RP (for use on rough/old surfaces to assist adhesion)

    Back to Earth: Tel: 01392 861763. Web:
    Product reference: TESCON VANA/ TESCON PROFIL single sided tape


  1. Admin - 2015-04-29 16:31:11 [Displayed version]

    DWG file uploaded.

  2. Admin - 2015-03-30 12:18:25

    Preview image and detail pdf updated.

  3. Admin - 2015-03-30 12:18:05

    Preview image and detail pdf updated.

  4. Admin - 2015-03-27 15:40:08

    EWI accessories and Air seal tape added.

  5. Admin - 2015-03-25 13:21:06

    General re-formatting. Introduction revised. Technical description updated and additional notes added. Parts list updated with suppliers links,

  6. Admin - 2015-03-10 11:58:57

    Version 2. - Intro/summary changed

  7. Admin - 2015-03-10 11:57:57

    First version

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