There are several different types of floor insulation, and each can bring different properties and characteristics to your project. In this blog we will explain why floor insulation should be specified, how it works and cover some of the types of floor insulation that are available.
The methods used to insulate floors depend on their construction and we will look at the most suitable type of insulation for each floor type. We will also cover other factors such as the importance of moisture management and how floor insulation can fit into a project’s sustainability goals.
What are the benefits of floor insulation?
If a property is uninsulated, when heating is needed during cold weather it can lose around 10 -20%[1] of its heat through the floor.
Floor insulation can help to increase the energy efficiency of a building and help to lower its energy bills. The EST (Energy Savings Trust) has published data[2] on the savings that are possible by adding floor insulation to an uninsulated floor.
Any increase in energy efficiency resulting from the installation of floor insulation can result in less energy being required to maintain the desired room temperature. Using less energy also may help to reduce any carbon emissions associated with that energy source.
Adding floor insulation can help to reduce draughts that can add to heat loss and also make the occupants feel less comfortable.
What are typical floor types that require floor insulation?
There are two main types of floors that require floor insulation.
Suspended timber floors
A suspended timber floor consists of timber boards laid over joists that span between supporting walls, creating a ventilated void beneath. This airflow can help prevent damp and rot, but without proper insulation the floor may feel cold and draughty. These floors were prevalent in homes in the beginning of the 20th century.
Concrete ground floors
With the increasing availability of Portland cement, reinforced concrete floors replaced suspended timber floors after the second world war[3]. Concrete floors are now the standard method of construction for new-build homes. They can either be constructed by laying a solid slab on the ground or by using precast concrete beams and infill blocks to create a suspended concrete floor. Whilst early concrete floors were not insulated, changes to Part L[4] of the building regulations in the year 2000[5] requiring lower U-values to be achieved in floors. This prompted the inclusion of insulation with the thickness of that insulation increasing in line with further changes to Part L to help increase energy efficiency.
What types of insulation are available for floors?
In the table below we list some common types of floor insulation and indicate where they are typically used.
Flexible Floor insulation
| Form | Floor type where most commonly used | Diffusion open or closed? | Density range (kg/m3)* | Typical lambda values (W/mK)* |
Mineral wool | Rolls or batts | Suspended timber | Open | 30 - 100 | 0.032 to 0.044 |
Glass wool | Rolls or batts | Suspended timber | Open | 10 - 20 | 0.032 to 0.044 |
Wood fibre | Batts | Suspended timber | Open | 50 | 0.036 |
Rigid Floor insulation | Form | Floor type where most commonly used | Diffusion open or closed? | Compressive strength (kPa)* | Density range (kg/m3)* | Typical lambda values (W/mK)* |
Wood fibre | Boards | Concrete ground floor | Open | 100-200 | 140 - 270 | 0.040 to 0.048 |
PIR | Rigid board | Suspended timber and concrete ground floor | Closed | 120-150 | 30 - 32 | 0.020 to 0.027 |
Phenolic | Rigid board | Suspended timber and concrete ground floor | Closed | 120 | Approx. 35 | 0.018 to 0.023 |
Extruded polystyrene (XPS) | Rigid board | Suspended timber and concrete ground floor | Closed | 300-700 | 28 - 41 | 0.033 to 0.036 |
Expanded Polystyrene (EPS) | Rigid board | Suspended timber and concrete ground floor | Closed | 70-250 | 10 - 35 | 0.032 to 0.038
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*Values stated in the table are typical and may vary from manufacturer to manufacturer – always check the declared product performance with the manufacturer. Values can vary due to different densities, formulations and manufacturing techniques.
What floor insulation is best suited to concrete ground floors?
As concrete ground floors are load bearing, the floor insulation that is installed must also be capable of bearing the typical loading experienced by the floor. Therefore, rigid insulation boards such as wood fibre boards with adequate compressive strength for the application are suitable for use in many concrete floor applications as they have a compressive strength up to 200 kPa.
The exact compressive strength requirement will be determined by structural engineers. It is likely to be higher for commercial applications where heavy machinery or vehicles add to the load on the insulation when compared to that of domestic projects. In this case insulation with high compressive strength such as EPS or XPS may be most suitable.
The thermal performance of the floor insulation is measured by its lambda value. The lower the lambda the lower the thermal conductivity of the insulation and the more it will help to improve the calculated thermal performance (U-value) of the floor.
Installing floor insulation that has a lower lambda than an alternative type in concrete ground floor applications can either be used to achieve:
- The required U-value for the floor with a thinner board or
- An improved U-value for the insulated floor
The choice will be project dependent. If there are any restrictions on floor height, then a thinner solution may be preferred. In some cases improving the U-value of the floor beyond regulatory requirements will be advantageous as it could allow more flexibility and choice when insulating other parts of the building fabric.
What floor insulation is best suited to suspended timber floors?
For suspended timber floors, insulation can be installed between the floor joists. Both rigid floor insulation boards and flexible insulation batts can be cut and installed between floor joists.
Unlike the concrete ground floor example, there is a limit to the thickness of floor insulation that can be fitted. This limit is determined by the depth of the floor joists. Therefore, insulation with a lower lambda value can lead to a lower calculated U-value for the insulated suspended timber floor.
As suspended timber floors are generally found in older buildings, the U-value requirements when retrofitting insulation are not as demanding as those for new build concrete floors. This means that many insulation types can be suitable.
However, when retrofitting insulation into existing buildings, especially older heritage buildings, there can be more focus on ensuring that moisture management is considered. In this case, for some projects, insulation that is diffusion open, such as wood fibre batts, may be preferred. This is to ensure that the existing conditions governing the free movement of moisture vapour are not compromised. If moisture is not correctly managed this can lead to condensation forming with the danger that long term damage could occur through damp, mould and eventually rotting timbers.
What regulations cover the installation of floor insulation?
Approved Document L – the conservation of fuel and power states the U-values required in both new and existing dwellings:
| New dwellings | Existing dwelling New fabric element | Existing dwelling Renovating existing element |
Target U-value W/m2K | 0.13 |
| 0.25 |
Limiting U-value W/m2K | 0.18 | 0.18 | 0.70 (known as the ‘Threshold Value’) |
Installing floor insulation when constructing new dwellings
In the case of new dwellings, the target value comes from the specification of the notional dwelling U-value for floors within Part L. This is a good starting point for specifiers to achieve compliance with the energy efficiency requirements of the building regulations, however, whilst it can be altered, the final value must not be worse than the limiting value of 0.18 W/m2K.
Retrofitting floor insulation in existing dwellings
Where work is done to an existing dwelling the U-value depends on whether the floor is a new or existing element. For the addition of a new floor where, for example, an extension is being added, the required U-value is the same as the limiting value for new dwellings at 0.18 W/m2K.
Where an existing floor is insulated the U-value target is 0.25 W/m2K, however, as there can be technical reasons why this may not be possible to achieve, a lesser standard may be appropriate as long as it is no worse than what is referred to as the ‘threshold value’ of 0.70 W/m2K.
What properties of floor insulation affect its suitability for projects?
As we saw from the table of different types of floor insulation, the compressive strength of the insulation can determine whether it is suitable for use in concrete floor applications.
We will run through some of the key properties of floor insulation to see how they can help decide which one is the best option for a project.
Diffusion open or diffusion closed floor insulation?
Ensuring measures are taken to control moisture is important when installing floor insulation. Using diffusion open insulation such as mineral fibre or wood fibre insulation can allow the floor to breathe. This may be best suited to older properties with suspended timber floors to match existing and established patterns of moisture movement.
Whether you choose diffusion-open or diffusion-closed materials, proper installation is critical to ensure the system performs as intended and air barriers and vapour control layers should be used where necessary to manage moisture within the floor structure. Moisture movement through the building fabric is inevitable and the long-term management of moisture can make or break the long-term health of the structure. Both diffusion-open and diffusion-closed insulation systems can deliver robust solutions as floor insulation, but if they’re poorly installed, they can lead to trapped moisture leading to potential mould growth and even structural damage of the floor joists.
How does floor insulation help with a building’s sustainability considerations?
Floor insulation can participate in improving the energy efficiency of a building by helping to lower its energy use. That in turn can reduce its operational carbon dioxide emissions that are the one of the sustainability drivers for many construction developments.
Where projects look at the carbon contribution of construction materials as a measure of their sustainability, the Environmental Product Declarations (EPDs) of different products can be used in the specification selection process.
The EPDs for wood fibre floor insulation boards consider that the wood used in their manufacture binds carbon dioxide equivalent CO2eq within the structure of each board.
Wood-based construction products effectively extend the duration of the naturally sustainable biogenic carbon cycle which can contribute to climate protection and help to meet sustainability goals.
However, as trees are the raw material for the manufacture of new insulation boards, they have bound more biogenic carbon from the atmosphere. Therefore, wood-based products are part of a short-term carbon cycle. Their major raw material does not add to long term carbon emissions unlike insulation based on raw materials that are extracted from reserves of minerals or petrochemicals that are not naturally replenished.
More information on wood fibre floor insulation solutions
STEICO manufactures wood fibre insulation boards and flexible wood fibre insulation batts that are suitable for use as floor insulation.
STEICObase has a compressive strength in excess of 150 kPa and can be used under floor screed systems. It is diffusion open using PEFC certified wood from responsible forestry with a lambda value of 0.048W/mk. As well as helping to improve thermal performance and hence helping to reduce the use of carbon emitting heating systems, each cubic metre of STEICObase binds up to 400kg CO2eq*and can thus contribute to climate protection.
Our STEICOflex 036 has a density of 50kg/m3 and lambda value of 0.036W/mk. It can be friction fitted between floor joists to provide diffusion open floor insulation for suspended timber floor applications.
To enquire about using our wood fibre insulation on your next project, please contact our expert team who will be happy to help.
*Calculation according to EN 16449, life cycle stage A1 according to EN 15804
[1]energysavingtrust.org.uk/energy-at-home/reducing-home-heat-loss/.
[2]energysavingtrust.org.uk/advice/floor-insulation/
[3]www.michaelhornsby.co.uk/assets/Uploads/documents/eehb-insulating-solid-ground-floors.pdf.
[4]assets.publishing.service.gov.uk/media/662a2e3e55e1582b6ca7e592/Approved_Document_L__Conservation_of_fuel_and_power__Volume_1_Dwellings__2021_edition_incorporating_2023_amendments.pdf
[5]great-home.co.uk/building-regulations-u-values-how-have-they-changed/