Ground floor ventilation to insulated floor [Version ID #273]

Author details

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Detail summary

Detail for ventilation of an insulated suspended timber floor. Required where existing air-bricks to sub-floor void will be blocked by floor insulation works. Periscopic vent should ensure continued clear air-path to sub-floor, to ensure adequate ventilation.

Technical description

Section detail. Ventilation to perimeter of floor insulation. Existing air-bricks blocked.


Before start of works:

Inspect any structural timbers, particularly those which enter external walls (e.g. floor joists); Inspect sub-floor, and timbers within for signs of damp and rot. Report immediately if any found. If possible record current condition of timbers and moisture content for future reference. Remove any organic matter from sub-floor and floor void. Ensure all existing air-bricks are unobstructed with clear ventilation path

Suggested Installation Sequence

  • Inspect floor void for signs of rot/damp and report immediately if found.
  • Carefully remove obstructions from below floor.
  • Seal between floor boards and fill gaps.
  • Friction fit insulation between between floor joists and fix in place.
  • Install webbing to hold insulation in place.

Reference Specification:

  • Air bricks in external walling to BS 493-1995, Class 1.
  • Gratings/ Ventilators in internal walling to BS 493, Class 2.
  • Pipe sleeves: Extend through full thickness of wall or floor, position accurately.
  • Generally: clearance around pipes: should be 20 mm (maximum) or diameter of service, whichever is the lesser.
    • Care should be taken to ensure air-tightness. Seal all service penetrations through existing wall. Lap and tape all membranes around edges of ventilation system. All insulation to be continuous to avoid thermal bridging. Please refer to Approved documents: B (fire safety): B1 section 1 (material alterations)/ B2 section 3 (internal fire spread), and Appendix A (material properties). Document A (structural safety) should be referred to when fixing/applying loads to existing floor joists or members. Ensure existing joists meet requirements in Approved document A (structural) before starting works. Refer to Doc L: L1B for dwellings; including all relevant amendments and L2b for works to all existing buildings that are not dwellings.

Parts list

  • Wall Ventilator [FL11c]

    Plastics air brick, colour to match existing finishes, cranked sleeve to suit and wall ventilator. Re-use existing airbricks where possible. As existing brick/blockwork. Outer face flush with wall face. \ Spaced at max. 2m centres to provide 1500mm2 of clear opening per 1m run of external wall.

    Contractors choice.

  • Skirtings and Wall/Floor Junctions [DP04]

    Standard decorators caulk between skirting and wall. Draughtex neoprene strips or timber fillet/ mastic seal between skirting and floor. Seal all junctions

    Draughtex. \ Reference: Draughtex Neoprene Strips

  • Woodfibre Insulation Between Floor Joists [FL01]

    Woodfibre Insulation. \ Thickness 200mm. \ Friction fit between joists to ensure air-tightness- cut batts approx 20mm wider than opening between joists. Supported by Polyester webbing drawn underneath insulation at approx 600mm centres, fixed to joists.

    Unger. \ Reference: UdiFLEX

  • Single-sided air seal tape [DP09a]

    Tape for junctions critical to air-tightness. 60mm (typical). \ Accesssories: ORCON F sealant and TESCON PRIMER RP (for use on rough/old surfaces to assist adhesion)

    Pro Clima \ TESCON VANA/ TESCON PROFIL (2 release tapes)


  1. Admin - 2015-04-30 11:18:14

    DWG file uploaded. General re-formatting.

  2. Admin - 2015-03-30 11:07:00

    Preview image and pdf detail file updated.

  3. Admin - 2015-03-26 12:50:20

    Parts list updated. General re-formatting.

  4. Admin - 2015-03-17 13:53:16

    Text formatted to lists where required and supplier links added.

  5. Admin - 2015-03-17 13:52:45

    Text formatted to lists where required and supplier links added.

  6. Admin - 2015-03-17 13:51:49 [Displayed version]

    Text formatted to lists where required and supplier links added.

  7. Admin - 2015-03-17 12:07:50

    Technical description updated.

  8. Admin - 2015-03-17 12:06:32

    Technical description updated.

  9. Admin - 2015-03-17 11:09:11

    Introduction updated. Technical description revised and updated with BS information and approved docs. Parts list updated with codes and additional parts added to specification.

  10. Admin - 2015-03-04 16:41:25

    First Version

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