Neil Turner, UK Technical Manager at Ecological Building Systems, looks at how suspended timber floors can be upgraded with more natural insulation to enhance the thermal performance of a home.

“When a home has a suspended timber floor, very often there is no insulation, which can lead to 10-15% energy loss. One of the most effective first steps to improve comfort and warmth is to add insulation beneath the suspended timber floor.

The rise of suspended timber floors

At the turn of the 18th century, construction methods evolved from laying timber floors directly on the ground, to building suspended timber floors above a ventilated chamber. This marked a significant innovation, as timber floors had previously been vulnerable to damp and rot due to direct contact with moist ground.

Now, built with an underfloor void that allows air to circulate freely, timbers remain dry and the structural integrity of the floor is preserved for longer.

Improving thermal efficiency

The most effective way to reduce heat loss in suspended timber floors is by insulating between the floor joists. Using a high-performance natural insulation, such as IndiBreathe Flex made from UK grown hemp and recycled jute fibres, is recommended. Thanks to its vapour-open and hygroscopic nature, this type of insulation can absorb excess moisture effectively, helping to regulate indoor humidity levels and reduce the risk of condensation forming.

Before installing the insulation, a fully windtight monolithic breathable membrane, such as Pro Clima Solitex Plus, should be laid over the joists and taped at the overlaps with Pro Clima Tescon Vana. Pipes or cables passing through the floor must be sealed using airtight grommets to prevent gaps or air leaks in the membrane.

For optimal performance, the insulation must be fitted tightly to eliminate air gaps that may cause heat loss. Cutting the material slightly oversized ensures a snug fit between the joists, helping it to stay securely in place and prevent snagging over time.

Another effective option for insulating suspended timber floors is wood fibre insulation, a dense and breathable material with hygroscopic properties.

Once the insulation has been installed, an airtightness membrane, such as Pro Clima DA, is laid over the top. By adding an airtight membrane, warm air is retained within the home while moisture can still escape, allowing the structure to breathe. This helps to maintain a healthy indoor environment and prevents damp or mould in properties.

All of the membrane overlaps should be sealed with an airtightness tool such as Pro Clima Pressfix, which applies pressure to airtightness tapes or adhesive membranes. This activates the glue to form a long-lasting seal.

Preparation is key

It is important to ensure proper preparation before installing any insulation to protect the building fabric and guarantee long-term performance. The area should be dry and free from any damp issues before work begins. Any rotting timber must be replaced to avoid future problems with damp and mould. It is also necessary to check for infestation bore holes or active infestation.

It is vitally important to ensure that adequate cross-flow ventilation is supplied via airbricks to the area beneath the floor, keeping the timbers dry and preventing decay. Where supporting walls are present, they should include gaps in the block work to ensure adequate air circulation. As part of the cross-flow ventilation requirements, it is essential to consider the following aspects: the size of the ventilation opening, the airflow path, the location of ventilation openings, the spacing of air bricks, and the use of mechanical ventilation in situations where it is not possible to install vents on opposite walls.

Once the floor is insulated, it will make a significant difference in energy performance, as well as comfort and will also reduce the carbon footprint of the home.

Benefits of insulating suspended timber floors

Upgrading insulated suspended timber floors can help manage moisture more effectively and make indoor spaces more comfortable.

By incorporating a ventilated space below the lower membrane, a suspended timber floor system helps to prevent moisture build-up from the ground, reducing the risk of damp, mould and timber decay.

When paired with breathable insulation and airtight membranes, suspended timber floors also perform exceptionally well in terms of thermal efficiency, maintaining a stable indoor temperature. This is particularly important in refurbishments aiming to meet or exceed modern energy performance standards.

Enhancing comfort without compromise

Upgrading a suspended timber floor doesn’t mean altering the visible character of the interior. The changes occur entirely beneath the floorboards, preserving the original look of the space while significantly improving how it feels.

Building occupants will notice a warmer and more comfortable living space, with reduced energy costs, all achieved without impacting aesthetics.”