A recent article in Business Day - ‘A testament to modern materials’ - stated that Light Steel Frame (LSF) lightweight walls “provide the magic” that afford a more energy efficient house solution to a luxury concept house at Monaghan Farm.
The article stated that this alternative building material is more energy efficient than a clay brick wall, and this conclusion was based on R-Value.
Wall thermal resistance (or R-values) are often misunderstood – even by professionals -and cited as a measure of energy efficiency. Many LSF waters and alternative Building Technologies (ABTs) cite their R-value measurement as proof of energy efficiency. However R-values have shortcomings.
Michelle Cerruti, Head of Residential at Saint Gobain referenced an unpublished CSIR study to make a case in favour of low mass building systems and against the thermal performance of high thermal mass, dense construction materials like standard brick masonry walling.
The weight of national and international scientific evidence does not support this claim.
International long term research findings
An Eight year Empirical Research Study at the University of Newcastle, Australia, continually measured internal temperatures of identical houses with different wall construction types under real world conditions. The findings were emphatic - walling with thermal mass consistently provided superior levels of thermal comfort and lower energy usage than the lightweight walling alternates.
For more detail please reference http://www.thinkbrick.com.au (Energy efficiency and the environment) - Edition 4.
The Thermal mass of clay brick keeps indoor temperatures within the comfort range for much longer in summer than insulated lightweight external walling is able to do. This results in less cooling energy used. In winter heat absorbed by the internal brickwork during the day, is then slowly released at night, reducing heating required.
In comparison the lightweight walls provide a hotbox effect as midday approaches on summer days adding to the cooling bill, and then cool down just as quickly after sunset requiring extra heating energy in winter.
The findings of the Newcastle studies correlate with a numerous thermal modelling studies undertaken in both South Africa and Australia, who share similar climates.
So what is responsible for the thermal performance of this home?
When all is said and done, the reported thermal performance of this undisputedly attractive house had absolutely nothing to do with the use of lightweight walling in lieu of high thermal mass clay brick walls as postulated.
Rather, congratulate the architect! The design and the application of intelligent Solar Passive Design interventions such as:
- orientation of the home on the site resulting in shading,
- placement of windows and door openings to capture the prevailing breezes and flush out the heat,
- the effectively sealing of door and window openings,
- the use of insulation in the building envelope,
- the use of double glazing with a 6mm cavity and
- the incorporation of alternate energy systems.
Using using the sun’s energy more effectively and optimising passive solar design principles have added real long term value to this home
In conclusion, thermal resistance or a walls R-value is an important thermal performance property in European climates where temperatures average less than 7°C throughout long, drawn out winters. Here in South Africa, R-values are only one measurement to consider. South African buildings exposed to long hot summer months require high thermal mass to achieve both optimum warmth in winter as well as cooling in summer.