Wall Insulation

Ballytherm Polyisocyanurate insulation is suitable for most wall constructions, including internally lined solid walls and masonry .cavity walls. 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.

wall insulation


Walls must be designed to prevent damage to the structure and to the health of the occupants as a result of water penetration.

There are three sources of moisture to consider:

  1. To prevent ground moisture rising into the building, walls must have an effective DPC which should be joined to any DPM. Where radon protection is required the radon barrier must extend to the outer face of the external walls: this may be achieved by using pre-formed cavity trays and sealing them to the radon barrier within the cavity. A DPC and radon barrier should not be set within the same mortar joint as there is a risk of creating a slip plane between the two membranes.
  2. Rain driven by the wind on to the surface of walls can penetrate to the building’s interior. The risk of water penetration is affected by the severity of the environmental conditions, the surface finish and joint treatment, and the type and positioning of the insulation. Because Ballytherm has a very low thermal resistance, a wall can have the required thermal performance with a residual clear cavity without a great increase in thickness. Further guidance is given in
BS EN 1996-2: 2006 (with national annex) and PD 6697: 2010.
  3. Water vapour can condense within walls as it passes from a warm interior to cold exterior. Ballytherm foil-faced boards can be of great benefit: in drylining, the joints between boards can be sealed with metalised tape to form a vapour control layer immediately behind the plasterboard. Condensation risk analysis should be carried out for all walls, using the method in ISO 13788: contact Ballytherm for details.

Thermal bridging

Maintaining continuity of insulation at the wall/roof junction can be difficult to achieve: with cold roofs (insulation between and above ceiling joists) fibrous insulation should be pushed between the rafters onto the wall head. In warm roofs (with rigid insulation in the plane of the rafters) Ballytherm insulation may be extended vertically from the wall head, between the rafters, to the underside of the roof insulation.

Openings should be detailed to ensure insulation meets door and window frames: setting the windows and doors behind reveals makes it easier to butt insulation to the framing and enables a better seal at the junction of the frame and wall.

Fixings, which penetrate wall insulation, such as wall ties or screws, will reduce the thermal performance of the insulation layer: the use of stainless steel fixings or plastic ties and fixings with small cross-sectional areas will minimise the effect.

Heating flues

Where flues from boilers and other heating appliances penetrate the walls precautions must be taken to avoid the hot pipe coming into contact with the insulation. There should either be a 25mm gap between the insulation and the flue – provided by a pipe sleeve – or a combination flue should be specified.

Wall insulation products

Insulating partial fill cavity walls Insulating drylined walls


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.