The long-awaited revision of the standard ‘Energy usage in buildings’ will see the incorporation of cavity walls into SANS10400-XA.
By TIPSASA | Photos by TIPSASA
Insulation is one of the most effective ways to improve the energy efficiency of a home or a building; insulation of the building envelope helps keep heat in during the winter and out in summer to improve comfort and save energy. Insulation also adds additional benefits such as creating a vapour barrier and / or an acoustic barrier.
Effective draught proofing, moisture control and ventilation are important at the design stage.
The appropriate level of insulation intervention depends on climate, building construction type and whether auxiliary heating and / or cooling is used.
Currently it is still unclear when the revision of SANS 10400-XA will be published as a Draft South African Standard (DSS) for public comment (which is usually 60 days). After the public comment closure period, all comments are evaluated by the South African Bureau of Standards (SABS) committee and once comments have been duly considered, it will be published. It is estimated that it may be published by the third quarter of 2019.
The Department of Trade and Industry (DTI) published an amendment to the National Building Regulations (NBR) to introduce the requirements for energy usage in buildings, which was promulgated on 9 November 2011.
All new buildings and building extensions from that date onward have to comply with the new regulation, yet many professionals still do not specify thermal insulation or do not comply with the minimum R-value requirements for the specific climatic zones.
Currently in South Africa, South African National Standards (SANS) recognises six main climatic regions or zones. This has been established as the benchmark for the maximum energy demand and maximum energy consumption in the design of a particular building under South African conditions.
The thermal performance of all components and systems (except windows and doors) are expressed in terms of R-values. For windows and doors performance is expressed in terms of U-values. Insulation materials are rated for their performance in restricting heat transfer, which is expressed as the R-value, also known as thermal resistance. The R-value is a guide to performance as an insulator – the higher the R-value, the better the insulation (such as resistance to heat flow) it provides.
The highest total thermal resistance for a roof assembly in order to comply with SANS 10400-XA is 3.7m²K/W. The minimum added R-value for thermal insulation in this roof assembly is 3.37m²K/W.
Nowhere does the standard refer to a one size fits all thickness. Products have different thermal resistance properties and must be tested in accordance with SANS 8301 ‘Thermal insulation – Determination of steady-state thermal resistance and related properties – Heat flow meter apparatus’, to determine the thermal resistance (R-Value).
Developers and contractors are the biggest culprits as they do not install insulation in roofs or, if they do, it is way below the requirements. Because the insulation is in the roof, no-one checks whether it is there or not and this is a very big challenge as there is no enforcement and ultimately it is the client or consumer who loses out on energy efficiency.
What is a cavity wall?
A cavity wall consists of two ‘skins’ separated by a hollow space (cavity). The advantage is that a cavity wall gives better ‘thermal insulation’ than a solid wall. It is as a result of the space provided between the two leaves of cavity walls which is full of air and reduces heat transmission into the building from outside.
This practice has already been followed in Cape province as cavity walls are also better for damp prevention than solid walls. The introduction of cavity walls nationally, is to satisfy regulatory requirements for building energy efficiency.
Since 2011 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. However, there is a case to be made for insulating the wall cavity at the time of construction. It makes no economic sense to build a cavity wall without adding thermal insulation as thermal insulation material cannot be installed in a cavity after a house has been built.
Why insulate cavity 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 such as Expanded Polystyrene (EPS), Extruded Polystyrene (XPS) and Polyisocyanurate (PIR) insulation boards can also prevent moisture transferring through the inner leaf. As the walls are warmer, condensation on the internal wall surface is eliminated.
Supporting the green cause
Most insulation products in South Africa either contain a portion or are produced using recycled products. For example, polyester fibre thermal insulation is produced using recycled PET bottles; glass wool insulation is made using recycled glass bottles; cellulose fibre insulation is made from chemically treated recycled paper; and expanded polystyrene uses a portion of recycled materials in its production. This process of utilising recycled material reduces the amount of waste products that are potentially exposed to the environment.