The merits of cavity wall insulation

by Tania Wannenburg
The merits of cavity

Cavity wall insulation can go a long way in satisfying regulatory requirements for building energy efficiency.

Specifiers, contractors, developers and new build clients are all exposed to the regulatory requirement for buildings to be efficient in their energy demand and usage.

Our country’s need to manage energy usage and emissions in terms of international protocols to which we are signatories, has led to the 2011 amendment to the National Building Regulations SANS 10400 XA and SANS 204. These require lighting and water heating interventions, as well as some thermal protection to resist heat flows inwards in summer and outwards in winter. Given modern building practices, this invariably means adding substantial amounts of insulation to particularly the roofing system.

The roof is considered as the main source of heat gain or loss, and is specifically addressed in the regulations, while floors are only regulated and insulated where underfloor heating is planned. Low mass external walls such as timber or steel-framed structures have stipulated minimum thermal resistance R-values to achieve, dependant on the climatic zone.

Masonry walls generally meet the requirements of the regulations and require no stipulated interventions. However, there is a case to be made for insulating the wall cavity at the time of construction, even in South Africa.

Why insulate the walls?
As houses become smaller, the ratio of roof to wall area decreases, making the walls more relevant in terms of heat flow in and out. Also, when extra floors are added, the wall area can far exceed the roof area and uninsulated walls rising above shading trees are more susceptible to direct heat impingement, particularly on the north, east and west sides.

Cavity wall insulation increases the thermal mass effect of the bricks and implies that the inner masonry leaf is at internal, rather than external, temperature. When heating or cooling the home, the insulated walls help to maintain the desired internal temperature for longer, and reduce the time and cost of achieving interior comfort.

Good thermal insulation also prevents moisture transferring through the inner leaf. As the walls are warmer, condensation on the internal wall surface is eliminated.

Getting it right
Cavity wall insulation really comes into its own when a competent person performs a rational design to minimise the energy demand and usage. Using cavity wall insulation will reduce the heat flows sufficiently to allow the designer to perhaps reduce roof insulation, and/or high-spec glazing interventions, which would otherwise be required if using the prescriptive route to satisfy the requirements of SANS 10400 XA. Beyond enabling considerable cost savings, performing a rational design allows the architect and client the freedom to have the design they choose.

IsoBoard XPS is an ideal insulator for use within cavity walls, given its high thermal and moisture resistance, and particularly its durability. IsoBoard will perform effectively for the life of the building, an important consideration when installing insulation that can never be replaced.

Isofoam SA (Pty) Ltd
Tel: 021 983 1140
Website: www.isoboard.com

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