To create functional and efficient buildings in line with regulations and best industry practises, it is essential to pay attention to the quality and construction of your architectural fixture and fittings. When it comes to glass for your aluminium windows and doors, we’ve compiled this information so you can establish how well the glass insulates a property and improves energy efficiency.
Determining the U-Values of the glass and complying with the National Energy Act may be easier than you think. The lower the U-Value rating of the aluminium window, the more efficiently it insulates heat loss / gain. What you need to do is determine the U-Value in relation to your relevant fixtures, and estimate their cost in relation to compliance.
Our current energy legislation in South Africa states that all fenestration must adhere to the air infiltration regulations as per SANS613. It also notes that in buildings whose windows comprise a smaller value than 15% of net floor area and are already compliant, you do not need to carry out any U-value calculations. In buildings where windows comprise more than 15% of the net floor area, the SANS204 energy standard must be applied, meaning that U-value calculations are compulsory.
(Please note that the improvements which we mentioned above are measured against the base of a standard aluminium window product with annealed or laminated glass.)
Low-E & Insulated Glazing, a high performance combination…
To achieve optimally efficient U-Values, Low-E (low-emissivity) glass or Low-E coating in combination with double-glazed units are appropriate.
Low-E glass out-performs all other coatings and tints. The coatings are designed to minimise the amount of ultraviolet and infrared light that can pass through glass without compromising on the actual visible light that it allows to pass through.
Product testing in accordance with SANS204 shows that the U-values of your windows can be reduced by 23%. You can do this by replacing regular annealed or laminated glass with Low-E glass. Simply doing this can be enough to comply with the National Energy Act when it comes to certain residential and commercial buildings.
Double glazing
In the last 30 years double glazing, also called insulated glazing (IG), has become a highly efficient method to shield your indoors from harsh outside climates. 
In double glazed units, two glass panes are separated by a space which is vacuum sealed and typically filled with dehydrated air. This system drastically reduces heat transference through the window units. For increased thermal performance, this vacuum-sealed space is often filled with inert gases like argon or xenon.
Double glazing can reduce the heat loss of a building by up to 50% The glass used can be laminated, or Low-E, depending on your preference and the building’s statute.
Significant decrease in U-values
Field testing in compliance with SANS204 indicated that a product’s U-values can be decreased by 45%. You can achieve this by simply exchanging single pane annealed units with appropriately configured double glazed units. In many residential and commercial buildings, this will adequately comply with the current National Energy Act.
We highlight the fact that Low-E glass or double glazing combined with Low-E glass, is by far the most exceptional and cost-effective method for enhancing a product’s U-value. Of course, the type of aluminium framing system that is used must also be taken into consideration.
Design makes a difference
Another important factor is the design of the window/door or curtain wall system. A cottage-pane design on a hinged door for example, will commonly test at a higher (worse) U-value than would the same door with just one pane of glass. You see, the bigger the surface-area of the aluminium profile compared to the area of exposed glass, the worse (higher) the general window / door U-value will be.
The role of thermally broken profiles…
A thermally broken aluminium frame system actually improves U-Values, here’s how: Standard aluminium is more susceptible to transmitting heat and noise. Inserting a reinforced polyamide or polyurethane bar between the inside and outside of the aluminium profiles is a game changer for the insulation properties of your aluminium profiles.
Further field testing in compliance with SANS204 indicated that a U-value can be dramatically reduced by 55% using double glazed Low-E windows with thermally broken aluminium frame configurations.
Rubber gaskets vs wool pile…
To comply with the air infiltration regulations of SANS613 and ensure that the test certificate for your windows is flawless, be sure to use EPDM or Santoprene rubber gaskets. Wool pile seals have been deemed as an inefficient sealing practice.
Calculation and Steps…
A relatively straightforward formula for calculating required U-values (SANS204) where zero overhang is assumed, goes as follows:
You must first calculate the net floor area of the building. Leave out rooms such as garages, garden storage, other non-heated internal compartments and internal walls. Include rooms such as wine cellars and servant quarters. Take the measurement from inside the external walls.
You should then take the following steps into the calculation: the total fenestration area (include glazed doors), the conductance target which equals to the floor area multiplied by the zone factor, and then the target U-Value, equal to the conductance target / fenestration area. Then you can identify the cost-effective aluminium system and glass that betters this U-value target.
Then you can repeat these calculations for every level of the building.
Using the above steps will show you that a conventional aluminium system with Low-E glass will be sufficient to comply with SANS204.
Confidently Compliant
We hope this explanation has given you an idea of the simplicity of calculating the required U-values for your building project.
(Please note that as per SANS Glazing regulations, it is the architect / building designer that calculates & specifies glazing/glass requirements. We can however advise but not specify.)
Remember that double-glazing, with the option of Low-E glass, and installed in a conventional configuration of aluminium framing provides the most cost-effective solution to make a building compliant with current energy statutes. The estimated cost of installation per square metre increases from base by up to 95% depending on the zone, orientation, floor area, window area and U-value required to comply.
Following these steps can make it much easier to comply with the SANS10400 and SAN204 regulations, so you can comply with new energy regulations, and stay on top of your game!
