Depending on floor construction and materials, cold floors can be inefficient and floor insulation can reduce the amount of heat lost. Significant improvement to U-values (tested in-situ), to both solid floors and suspended timber floors can be achieved following insulation.  However, the potential for application and improvements are subject to the floor and condition. Floor insulation, such as adaption of skirting boards, door frames and architraves with solid floor insulation, can also be disruptive, with consideration of the detail and materials necessary to ensure there are no resultant performance issues.

Non-intrusive options include draughtproofing for timber floors. The use of fabrics such as rugs and floor coverings have been noted for increasing occupant comfort, particularly with cold solid floors, such as flagstone floors that generally should not be altered, or suspended timber floors that introduce cold air from below.

Suspended timber floors

Where appropriate, insulation to suspended timber floors can be achieved by installing insulation between joists. To minimise disruption, floor insulation should be installed from below, where this is achievable.  In some instances, insulation can be applied from the top, however this requires the floorboards carefully being removed and then re-laid. This can impact and damage the timber so cannot always be achievable, particularly where it is decorative.

Ventilation under the timbers is an important consideration. If there are any air bricks or vents that are located underneath the flooring that can be noted from the external elevations, these must not be covered as this would have a significant impact to the building’s performance and would result in an accumulation of condensation and moisture.

Non-permeable insulating materials and boards should not be used on top of a timber floor or between joists as this will affect the moisture movement and can trap water vapour leading to deterioration and decay. Natural materials, such as wood fibre boards, would mitigate some of the risk, but still require appropriate detailing and careful installation.

Solid floor

Solid flagstone floors, or similar, can be easily damaged when lifted so may be difficult to install insulation underneath. No insultation should be installed on top of the flooring as it would be likely to have a detrimental impact to the floor.

If the original floor has been lost and it is now a concrete floor, rigid insulation can be laid on top. If a concrete floor needs to be removed, particularly if it is resulting in damp issues and affecting the performance of the building, installing an insulated lime concrete, sometimes with a foam glass floor, could be considered. This can be installed with underfloor heating systems, which can be more energy efficient.

Materials

As with all insulation, materials are key to ensure there will be no deterioration of fabric. A vapour permeable material is required and natural materials such as hemp and wood fibre board, are often most appropriate to ensure there is no accumulation of moisture. As with most insulation, synthetic options with closed cell systems, are not vapour permeable and therefore, can adversely affect performance.

In difficult to reach areas, spray foams are often considered as they can be achieved mechanically by a robot. However, this has a detrimental effect to a building fabric and its qualities, and therefore is not compatible with traditional buildings. Spray foams are not reversible and highly chemical; there use could also lead to issues with air quality and occupant health.

Further information on insulating floors

Suspended timber floors

Historic England’s Insulation of suspended timber floors

The SPAB’s Suspended timber floor insulation

Department for Business, Energy & Industrial Strategy, Retrofit insulation for suspended timber floors: best practice

Simple Energy Advice, Suspended floor insulation

STBA, Floor insulation between/under floor joists

STBA, Floor void filled with insulation

STBA, Exposed soffits to upper floors: Insulation in between joists or under soffit

Solid floors

Historic England’s Insulating solid ground floors
Simple Energy Advice, Solid floor insulation

STBA, Replacement of existing ground floor with new concrete insulated solid ground floor

STBA, Floor Insulation on top of existing floor finish