Thermally Upgrading Single Leaf Masonry Walls With Internal Wall insulation...What Are The Pitfalls?

Identifying areas and elements within existing buildings where substantial improvements to the thermal performance can be affected, will always present a variety of challenges. The reason for this is that most of the material used in older buildings exhibit very different characteristics than most modern building materials especially in the areas of vapour diffusion, “breathability” and moisture management. One such area of contention is the thermal upgrade of single leaf masonry walls with internal insulation. 

For specifiers, it is critical to assess the existing wall in order to select a durable thermal solution. Gerry, an Architect from a Cork based practice asked the following question regarding this issue:

"On a single leaf masonry wall what are the key items to be assessed prior to applying internal wall insulation systems?"

There are many items to consider prior to specifying internal wall insulation on solid masonry walls, a number of which are:

• Ensure that the wall is not suffering from existing moisture ingress issues (i.e. due to poor drainage externally, poor maintenance of water goods or inappropriate or poorly maintained external plaster or pointing.)  If it is, this must be addressed prior to any installation commencing. 
• Is there existing external plaster on the wall or is it exposed brick or stone?
• Is the existing plaster lime or cement based?
• How exposed is the building?
• How thick is the wall?
• What is the stone type and what is the approximate proportion of mortar to stone or brick?
• Is there an internal plaster and if so what type?
• Consider the potential for thermal bridging between solid internal walls, windows doors and floors, to external walls.

Following an assessment of these points, I would recommend to that the long term impact of thermal insulation on the wall be assessed with a numerical simulation in accordance with IS EN 15026 2007, as opposed to the conventional Glaser method (IS EN 13788). The numerical simulation method provides much higher levels of accuracy for such constructions. This can be carried out with hygrothermal simulation software such as WUFI Pro or Delphin.

In such scenarios it is recommended to apply thermal insulation materials which significantly reduce heat loss and at the same time reduce the risk of long term moisture accumulation within the structure. Materials which fulfil these criteria may be woodfibre boards, such as Gutex Thermoroom or calcium silicate capillary active insulation, such as Calsitherm. In some cases a sealed humidity variable vapour control layer, such as Pro Clima Intello Plus, combined with a natural insulation, such as Thermo Hemp between battens may be used.

This can be validated with a numerical simulation tool, such as WUFI Pro.