Insulating Below Suspended Timber Floors – Design Guidance

Any radon barrier should be installed within the concrete covering of the void beneath the floor and should extend across the entire footprint of the building.

To ensure the insulation extends to the perimeter of the floor Ballytherm Insulation should be packed between the inner surface of a wall and the joist, which runs next to it (figure 15).

Service penetrations should be designed out wherever possible: at any unavoidable penetrations the Ballytherm boards should be cut neatly to accept the pipework or cable and the remaining gap sealed.

An alternative method is to fit the Ballytherm boards at the base of the joists to form a series of service voids (figure 16).

a. radon barrier (if required)  b. Ballytherm Insulation packed between inner surface of wall and joist 

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