Insulating Below Suspended Timber Floors

Insulating below suspended timber floors

The thermal performance of timber floors may be improved by fitting installation between the joists, immediately beneath the deck. This construction may be used to upgrade existing floors or to create new floors. Timber floors in extensions can be easily matched to the levels of existing floors.

The properties of Ballytherm Insulation match those required for this application: it is robust and self-supporting, whilst it’s low thermal conductivity minimises the thickness of insulation between the joists.

The Ballytherm boards are installed between the joists, resting on battens fixed to the sides of the joists or on nails. The boards may be set either directly under the flooring with no air gap or, close to the base of the joists, leaving voids between the boards and the flooring.

In the latter construction the reflective surface of the boards will result in a series of low emissivity air spaces, which will cut the rate of radiation heat loss across the cavity and improve the thermal performance of the floor.

The thickness of Ballytherm insulation required to meet regulations may be determined from table 7.

Table 7

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 or use our contact form.

Floor Insulation

Design Guidance