Floor Insulation
Solid or suspended historic floors, where repaired and maintained with appropriate materials, are inherently resilient and will continue to perform well even after a flood event. However, in the drive to minimise carbon emissions and energy use by reducing heat loss, floors may need to be insulated.
For buildings at risk of groundwater flooding, floor insulation is not recommended. There is currently no insulation material that continues to be thermally efficient in the presence of moisture. Carpets and other floor coverings have been shown to reduce heat loss in homes by 2 per cent. They can also easily be removed and stored away during a flood.
Floors can be insulated in several ways when either not at risk of flooding or at very low risk of a flood event occurring. The choice of insulation is informed by the construction of the floor and hygroscopic considerations.
The efficacy of insulating floors is still being researched. Leeds Beckett University et al and DESNZ in the DEEP project (2024) identified that heat loss through floors is more complex than heat loss through other building elements. With suspended floors, the impact of subfloor ventilation creates further challenges. Whether insulating a floor in a flood risk zone or not, all ventilation requirements and moisture risks must be considered.
Insulating suspended floors
Installing insulation between the joists of a suspended timber floor will more readily facilitate post-flood drying of the building fabric as they can be readily removed either prior to a flood, or after a flood has occurred and refitted once the property is dry. This option is time consuming to the occupant and may not be a desirable process but should be discussed.
However, it is important to note that evidence suggests installing insulation under a timber suspended floor has the potential to increase overheating risks to the property in the summer months.
Insulating solid floors
Insulating solid floors would require the wholesale replacement of the existing floor, is quite expensive and will be carbon intensive for only a marginal thermal benefit. However, where a building has no existing floor, or a floor that needs replacement due to structural failure the following is relevant.
In many situations a capillary break (stopping the movement of liquid moisture) is recommended when insulating a solid floor. Thus it is important to establish whether a material will be used as a capillary break or as an insulator. Aggregates such as foamed glass cannot perform both functions simultaneously, because once liquid moisture is present it is no longer able to act as a thermal layer. In line with manufacturer guidance, foam glass should be installed at a minimum of 300mm above the highest point of groundwater if it is to be used as thermal insulation.
An option could be to install this system with a damp-proof membrane (DPM) which may stop groundwater reaching the foam glass aggregate allowing it be used as a thermal layer. However, it is important to be aware that DPMs can be breached during a flood and can also cause moisture to move to other parts of the building, such as the base of walls.
Alternatively, foam glass aggregate may be used as a capillary break where water from the ground needs to be separated from the floor. In this situation, it is accepted that the aggregate is not acting as an insulator. The floor screed is the only insulating factor, unless other insulation is also in place.
Geotextile membranes are often recommended when a new solid floor is laid. These membranes are used in both construction and landscaping projects, but they are most common in drainage and engineering works. They can act as a filter between different materials and also stabilise the ground beneath them. However, they have a propensity to become blocked by silt and retain water in certain locations. As they do not impede the movement of moisture, they would not protect the insulation from floodwater or ground moisture thus meaning the insulation will not provide any thermal efficiency. Their purpose is purely to be a separation layer between different materials underground.