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 + 353 (0)49 95 27000, or email us at info@ballytherm.ie.



Floor insulation must be able to withstand the deadload of the floor construction and the imposed loads resulting from occupation of the building. Ballytherm has a sufficiently high compressive strength for it to be used in domestic projects.

Consult Ballytherm for advice on using the material in projects with more demanding loadings.

Thermal bridging

Improved standards of thermal insulation within building elements have focussed 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

U-values for ground floors are calculated according to EN ISO 13770: 2007. Because the ground has an innate thermal resistance the overall thermal performance of the floor depends upon the floor’s dimensions and form factor, represented by the ratio P/A (the floor perimeter, P, divided by the floor area, A) as well as the insulation and other layers in the construction.

The thickness of Ballytherm Insulation required to meet the U-values required by regulations is shown in tables 4, 5, 6 and 7. To use the tables, calculate the ratio P/A and consult the appropriate column in the table. Contact Ballytherm for U-value calculations for other floor constructions.

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 naturally occurring gas, which is generated during the radioactive decay of uranium to lead. High concentrations of radon can cause cancer.

For the most part radon percolating to the surface disperses harmlessly in the atmosphere; however, radon generated beneath buildings can seep in through gaps and cracks in the structure and build-up to dangerous concentrations. To protect building occupants from risk of harm, buildings in at-risk areas must include radon protection measures*. The minimum measure will be the provision of a radon barrier across the entire footprint of the building.

The detailing of the barrier will depend upon the floor construction, but in many cases one membrane can act as damp- proof membrane (DPM) and radon barrier. Difficulties can arise at external walls, where the radon barrier has to be carried across a cavity: one solution is to seal the radon barrier to a gas-proof damp-proof course (DPC), which is stepped down from the inner to outer leaf.

For details of radon protection measures refer to:

  • BR 211. Radon: guidance on protective measures for new buildings. 2007.
  • Radon in the workplace. A guide for building owners and managers. 2011.
  • HomeBond House Building Manual. 7th edition.

* In the Republic of Ireland all new dwellings must include a radon barrier. In England and Wales, Scotland and Northern Ireland radon protection measures are required in areas assessed as high risk.

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 + 353 (0)49 95 27000,, email us at info@ballytherm.ie or use our contact form.