External wall – below DPC

External wall – below DPC

The external walls of a building continue below ground level, to be supported on the building’s foundations. Where the wall is insulated externally or in the cavity, masonry acts as a thermal bridge between the ground floor insulation and the wall insulation – it is impossible to achieve complete continuity of the thermal envelope from one element to the other.

Construction techniques for traditional building methods are well-established. For projects pushing at the boundaries of low-energy construction and sustainable building, however, new solutions must be found using existing materials. The junction between the ground floor of a building and its external walls is an excellent example.

What Polyfoam XPS products are suitable for an external wall below DPC?

Whether installed between the external face of the wall and the ground, or below the damp proof course within a masonry cavity, Polyfoam Floorboard Extra offers the thermal performance and robustness required to deliver long-term thermal performance to hard-to-insulate foundation details.

Polyfoam XPS Ltd is a leading manufacturer of closed cell, extruded polystyrene (XPS) insulation. The Polyfoam range is lightweight, strong, moisture resistant and easy to cut and shape, providing thermal performance and strength for the lifetime of the building. Product benefits include:

  • High compressive strength.
  • Highly resistant to water absorption.
  • Robust and long term dimensional stability.
  • Environmental Product Declaration.
  • BES 6001: Responsible Sourcing of Construction Products.

What are the demands on thermal insulation below damp proof course (DPC) level?

Specialists in low-energy construction methods, such as the Passivhaus standard, have developed floor/wall junction details featuring greater levels of insulation, to minimise the thermal bridging effect.

Below damp proof course level is a potentially hostile environment for most common external wall insulation materials, as they are not tolerant of damp or wet areas. Furthermore, when installed below ground level, the insulation material can also be subject to soil pressure or ground heave.

Extruded polystyrene insulation boards not only offer superior load-bearing performance, but are unique in being tolerant of damp or wet environments. Their thermal performance is not impacted by the conditions, meaning the junction detail will consistently perform as designed for the life of the building.

Recommended Polyfoam XPS products for external walls below DPC are: