Stand Alone External Floor insulation to Perimeter

Author details

Original Author:Admin Organisation:Retrofit Pattern Book

Detail summary

Detail for stand alone perimeter insulation to edge of ground floor on outer face of external wall. Designed to insulate an existing solid floor by providing sufficient perimeter insulation to footings in order to mitigate cold bridging through the external wall.

Technical description

Section detail. Perimeter floor insulation for solid floor with perimeter/plinth insulation. Excavation required to footings or 600mm below ground level with new drainage layer infill and flagstone over. External render to perimeter insulation and cill detail to allow water runoff.

Suggested Installation sequence:

  1. Dig trench to footings or 600mm.
  2. Adjust services as required.
  3. Fix insulation to external wall face.
  4. Render outer face of insulation above ground level.
  5. Fix cill.
  6. Backfill to create drainage layer.

Reference Specification:

Extruded polystyrene perimeter insulation, suitable for below ground use and drainage, layer; to BS EN 13164.

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.

Please refer to Document A (structural safety) as reference for the condition of existing floor joists or members. Ensure existing joists meet requirements in Approved document A (structural) before starting works.

Refer to approved document C (resistance to contaminants and moisture) with reference to below ground works. Refer to approved document H (drainage and waste disposal), section H3, rainwater drainage in addition.

Documents L1b of Part L (conservation of fuel and power) 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 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

  • External Perimeter Floor Insulation [FL04]

    Extruded Polystyrene (XPS) to BS EN 13164. 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.

  • Proprietary Render For EWI [FL04]

    To match render to external insulation if elsewhere on property.

    As EWI insulation system manufacturer.

  • Sill To External Insulation [FL04]

    Self-finished aluminium to suit 200mm insulation. Smooth finish. Colour to suit render finish.

    Contractors choice

  • Granular Backfill drainage layer [EW01]

    • Material: 20 mm washed and graded aggregate providing 30% voids.
    • Minimum Thickness: As drawing.

    Contractor's choice

  • Concrete Flag Paving (Optional) [FL04]

    Use reclaimed paving where possible. Natural finish to match existing where present. Smooth. Size: to cover drainage layer.

    Contractors choice


  1. Admin - 2015-04-30 13:57:50 [Displayed version]

    PDF updated to match dwg file

  2. Admin - 2015-04-30 11:15:04

    Reformatting of [FL04] contact details on parts list. DWG file uploaded.

  3. Admin - 2015-03-30 11:14:34

    Preview image and pdf detail file updated.

  4. Admin - 2015-03-26 13:59:20

    General re-formatting. Introduction updated. Technical description updated with approved document links and additional notes. Parts list updated with suppliers links.

  5. Admin - 2015-03-17 10:57:25

    Version 2. Introduction expanded. Technical description updated and expanded with BS codes and relevant approved docs. Parts list updated with relevant codes.

  6. Admin - 2015-03-04 16:29:27

    First version

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