Last edited 07 Nov 2016

Floor insulation

Contents

[edit] Introduction

In the average home, approximately 10% of the heat loss is through the ground floor. Therefore, insulation as a means of reducing heat loss is typically installed on the ground floor. However, it may also be provided in upper-floors between heated and unheated areas. In comparison with wall insulation or roof insulation, savings associated with floor insulation are more modest, but under some circumstances, installation costs can be lower.

The installed performance of an insulation product is dependent on:

Commonly-used floor insulation materials include:

[edit] Building Regulations

Legislation such as the building begulations part L has acted as a catalyst for insulation, along with advanced voluntary programmes such as the Code for Sustainable Homes and BREEAM.

The building regulations require that floors achieve minimum thermal performance values (U-values – a measure of how quickly heat will travel through the floor), and this affects the amount of insulation required. For example, achieving a U-value of 0.25 W/m2K or less. would require at least 70mm of high-performance foam insulation, or 150mm of mineral wool, (although this will vary depending on floor type, construction, shape and size).

Calculations by Kingspan have produced best starting point values that are thought to be suitable for common situations.

[edit] U-values for floors in domestic buildings

England – April 2014

  • New Build: Best starting point (fabric only) – 0.11
  • Existing buildings: Extension – 0.22
  • Existing buildings: Refurbishment – 0.25

Wales – 31st July 2014

  • New Build: Best starting point (fabric only) – 0.15
  • Existing buildings: Extension – 0.18
  • Existing buildings: Refurbishment – 0.25

Scotland – 1st October 2015

  • New Build: Best starting point (fabric only) – 0.13
  • Existing buildings: Refurbishment and extensions (where existing dwelling’s walls and roof U-values are worse than 0.70W/m.K in the walls and worse than 0.25 W/m.K in the ceiling) – 0.15
  • Existing buildings: Refurbishment and extensions (for other extensions, upgraded existing thermal elements, non-empty conservatories and conversion of unheated buildings) – 0.18
  • Existing buildings: Conversion of heated buildings – 0.25

[edit] U-values for floors in non-domestic buildings

England – April 2014

  • New Build: Best starting point (fabric only) – 0.18
  • Existing buildings: Extension – 0.22
  • Existing buildings: Refurbishment – 0.25

Wales – 31st July 2014

  • New Build: Best starting point (fabric only) – 0.22
  • Existing buildings: Extension – 0.18
  • Existing buildings: Refurbishment – 0.25

Scotland – 1st October 2015

  • New Build: Best starting point (fabric only) – 0.15
  • Existing buildings: Refurbishment, extensions and conversion of unheated buildings – 0.20
  • Existing buildings: Conversion of heated buildings – 0.25

NB See PA ratio for more information.

[edit] Insulation methods

[edit] New buildings

[edit] Insulation above the floor slab

Insulation is placed above the concrete slab, along with a separating/slip layer and then a rigid floor which is generally either screed or boarding. The damp proof membrane (DPM), which can be either above or below the slab, must be continuous with the damp proof course (DPC) in the surrounding walls. The insulation boards must be tightly butted and sealed to limit air leakage. Heating response time is improved by having the insulation above the slab, and the insulation zone can be used to run services and underfloor heating. However, when used together with timber-based flooring it may be unsuitable for use in rooms that may get wet such as kitchens or bathrooms.

[edit] Insulation below the floor slab

Insulation is placed below the concrete floor slab. There are fewer restrictions on the thickness of the insulation in comparison with above slab insulation, and there is less of an issue with point loading as the load is spread over the slab rather than the insulation. However, rooms are slower to heat by comparison with above slab insulation.

[edit] Timber floor

The installation process follows the same method as that detailed below, although the process is easier as there is no existing flooring to remove or gain access to.

[edit] Retrofitting existing buildings

Simple draught-proofing: Sealant or caulking can be used to fill the gaps between floorboards and between skirting boards and the floor.

Timber floors: Older homes are more likely to have suspended timber floors (with no ceiling below). These can be insulated by raising the floorboards and laying mineral wool insulation supported by netting between the joists. This process is relatively easy if there is a cellar or an access hatch allowing entry to the crawlspace (void) below the floorboards. If not, the floorboards will need to be taken up. It is important to consider the propensity of timber floors for air leakage. Attention is needed when relaying old floorboards or installing new ones, to ensure that all joints between boards are adequately sealed.

Upgrading an existing concrete floor slab: Newer homes are far more likely to have a ground floor made of solid concrete. The simplest method of installation is to add insulation and a new floor deck on top of the existing floor. However, raising the floor level will usually require floor coverings skirtings, radiators and electrical fittings are removed and re-fitted, as well as reducing the heights of doors.

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[edit] Related articles on Designing Buildings Wiki

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