EWI Perimeter insulation to footings

Author details

Original Author:Admin Organisation:Retrofit Pattern Book

Detail summary

Perimeter insulation detail for external wall insulation down to below ground level. Detail for junction between EWI and XPS perimeter insulation for below ground use, providing 600mm maximum insulation below the depth of the internal floor level.

Technical description

Section detail. EWI detail junction at ground level. Continuous to avoid thermal bridging.

Suggested Installation Sequence:

  1. Excavate perimeter channel
  2. Remove existing airbricks
  3. Fix woodfibre wall insulation insulation
  4. Install air vents and perimeter insulation
  5. Render
  6. Back fill perimeter channel.

Reference Specification

Perimeter insulation suitable for below ground use and drainage layer. To BS EN 13164

Rainwater drainage: please refer to Document H (drainage and waste disposal); and Approved document C (resistance to contaminants and moisture), with reference to Section 2, and section 6; for guidance.

Drainage layer: Granular infill free from excessive dust, well graded, all pieces less than 75mm in any direction, minimum 10% fines value of 50 kN when tested in a soaked condition to BS 812-111. In one layer no more than one of the following:

  • Crushed rock (other than argillaceous rock) or quarry waste with not more binding material than is required to help hold the stone together
  • Crushed concrete, crushed brick or tile, free from plaster, timber and metal.
  • Crushed non-expansive slag
  • Gravel or hoggin with not more clay content than is required to bind the material together, and with no large lumps of clay.
  • Well-burned non-plastic colliery shale.
  • Natural gravel. /Natural sand.


Care should be taken to ensure air-tightness. Seal all service penetrations through EWI and existing wall. Lap and tape all membranes around edges of EWI system.

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

  • Woodfibre EWI adhesive [EW01]

    Adhesive for use at joint between perimeter/ plinth insulation and external wall insulation.

    Back to Earth. Tel: 01392 861763
    Web: http://www.backtoearth.co.uk/
    Product Reference: UdiSpecial Adhesive.

  • External Wall Insulation (Woodfibre), 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-Diffutherm. Product Reference: UdiFRONT.
    Supplied by: Back To Earth. Tel: 01392 861763
    Web: http://www.backtoearth.co.uk/

  • External Perimeter Floor Insulation [FL03]

    Extruded Polystyrene (XPS) suitable for below ground conditions and for application of render.

    • Thickness: as EWI.
    • Depth: Minimum 600mm below internal floor level.
    • Thermal conductivity: 0.033W/m2k. GWP: <5.
    • Joints: Tight butt joints

    BASF. Product Reference: Styrodur 2800C insulation.

  • Lightweight Aggregate Insulation bounding layer [FL03]

    Lightweight recycled glass aggregate.

    • Thermal conductivity: 0.08W/mk
    • Depth: As perimeter insulation. (min 200mm)
    • Width: 200mm.

    Available recycled glass aggregate (or similar) products

  • Proprietary Render For XPS Insulation System [FL03]

    To match render to external insulation above

    Render: to match render of external insulation above.


  1. Admin - 2015-04-29 11:32:33 [Displayed version]

    General formatting changes and DWG file uploaded.

  2. Admin - 2015-03-27 16:25:51

    Preview image and .pdf file updated.

  3. Admin - 2015-03-23 16:35:09

    General re-formatting. Parts list updated with links and suppliers details.

  4. Admin - 2015-03-12 16:51:53

    Version 4. Parts list updated

  5. Admin - 2015-03-12 16:50:25

    Version 4. Parts list updated

  6. Admin - 2015-03-12 16:42:04

    Technical description updated and expanded. BS and Approved doc information added. Parts list added.

  7. Admin - 2015-02-27 15:14:59

    version 1

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