Floor Insulation

Ballytherm Polyisocyanurate insulation is suitable for a variety of floor construction types, such as precast concrete, suspended timber and ground bearing concrete. The pages within this section provide design guidance, design details, installation instructions and advice on sitework.
Custom sizes are also available on all product ranges. For more information call our insulation experts on 0800 644 6900, or email us at info@ballytherm.co.uk.



Every floor is going to carry the dead load of the people, furniture and possibly heavy equipment occupying the building. The floor insulation must therefore be up to the task. The high compressive strength of Ballytherm makes it capable of being used in those constructions.

Thermal Bridging

Improved standards of thermal insulation within building elements have focused attention upon the amount of heat lost at junctions between elements where there is no continuity of insulation or there are exposed heat paths.

The simplest method to avoid thermal bridging at the floor/wall junction is be to ensure the insulation in the two elements meet. Where structural considerations make that impossible, for example when the wall insulation is inside a cavity, thermal bridging may be avoided by continuing the floor insulation vertically at the perimeter of the floor so it overlaps the wall insulation. The minimum thickness of Ballytherm boards for edge insulation is 20mm. It is sometimes more convenient to use the same board thickness as specified for the rest of the floor.

Thermal Performance

The thermal performance of any given floor is calculated using the dimensions of the floor, the insulation and other construction materials used to build the floor. The U-values for floors are determined by EN ISO 13770: 1998. How thick Ballytherm Insulation must be to meet these values is available in Table 4 (Below Ground Bearing Slabs), Table 5 (Above GroundBearing Slabs), Table 6 (Above Pre-Cast Concrete Floors) and Table 7 (Suspended Floors).  First, calculate the perimeter of the floor divided by the area of the floor and then find the corresponding entry in the tables.

In order to have complete thermal insulation, the construction must focus on the heat that can be lost between flooring elements, such as at doorjambs where one floor meets another. To ensure that these thermal bridges do not exist is to make sure the insulation of one floor seamlessly meets that of the next. Bring Ballytherm Insulation up slightly into the walls to protect against gaps at the base. Overlap where it is necessary to mitigate heat loss from gaps in insulation.

Building Regulations and Standards

Building Regulations and Building Standards set targets for the overall energy efficiency of buildings, as well as setting limiting U-values for building elements.

The U-value tables on this website indicate the maximum area-weighted U-values permitted by local regulations. However, it may be necessary to achieve U-values lower than those shown, in order to attain the whole-building energy efficiency target.

Radon Protection

Radon is a gas that appears when uranium decays into lead. When this gas is present in high concentrations, it leads to cancer. This occurs naturally in the soil and can make its way through under floor insulation into buildings. If it becomes trapped in gaps in construction, it can build up to deadly levels.

To ensure that people inside of these buildings are protected against Radon, construction in at-risk Radon locations must have protective measures against it. The most basic of these measures is a Radon barrier beneath the entire building. A single layer of the right material can provide a damp proof shield and a Radon barrier.

For more information about Ballytherm underfloor insulation and its properties, talk to one of our insulation experts! Call 0800 644 6900, or email us at info@ballytherm.co.uk.

Table 04
Table 05
Table 06
Table 07

Floor Insulation Products

Insulating below a ground bearing slab Insulating above a groundbearing slab
Insulating above precast concrete floors Insulating below suspended timber floors


Further Advice & Information

For more information about Ballytherm products, technical advice, or guidance on the suitability of our products for your project, contact us at 0800 644 6900,, email us at info@ballytherm.co.uk or use our contact form.