Insulating Between And Below The Rafters

“…is well suited to projects where the roof covering is being stripped off and replaced…”

Ballytherm insulation may be used to form warm pitched roofs when applied between and below the rafters. Applying a layer of insulation beneath the rafters avoids the use of long fixings and enables all the insulation to be applied from inside the roof.

This method is well suited to new build projects and to refurbishments where the roof covering is being stripped off and replaced.

The properties of Ballytherm insulation match those required for this application: its low thermal conductivity minimises the thickness of insulation required, whilst it is strong enough to span the distances between the rafters without bowing. The Ballytherm boards should be set in two layers, one set between the rafters and the second extending in a continuous layer across the underside of the rafters and restrained by battens.

The insulation is protected by the internal finish. The reflective surface of the boards reduce radiation heat loss across the air spaces and further improve the thermal performance of the roof.

The thickness of Ballytherm insulation required to meet regulations may be determined from table 11.

Table 11

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