The glass installed in the windows, skylights, and external doors substantially affect the thermal performance of a residential structure. In fact, details of glazing (glass and frames) constitute an important part of the BASIX certificate and the NatHERS assessment.
Without proper glass installation, residential structures can lose up to 40% of heating energy and gain almost 87% of heat through windows.
Optimising the thermal performance of the window and door glass increases the internal comfort of your home and reduces energy consumption for artificial heating and cooling. Consequently, the occupants of the residential property enjoy reduced operational costs and greenhouse gas emissions.
Similarly, for commercial buildings, DTS assessment and JV3 modelling are applicable for evaluating energy performance.
Why Selecting The Right Glass Is Necessary For Attending BASIX Certification?
- Correct glass installed strategically allows natural light and offers spectacular views connecting interior living spaces with the outdoor world. Natural light reduces dependency on artificial light fixtures, thus making the building energy efficient.
- The cost of glass installations for windows and skylights and the heating and cooling expenses of a residential structure are closely related. An initial investment in optimal and high-quality glass can considerably reduce annual expenses on artificial heating and cooling.
- Energy efficient glasses also minimise the peak heating and cooling load, leading to a reduction in the size and capacity of the air conditioning system by approximately 30%. Thus, saving more costs.
All of these are important considerations in the energy-efficiency and thermal comfort section of the BASIX certificate.
To identify the best class for your residential project, let's take a deep dive into the different types of glass properties applicable for window glazing.
Understanding Important Glass Properties For Windows
Visible Light Transmittance
Signifies the amount of sunlight passing through the glass. A low visible transmittance can be beneficial for reducing heat gain from direct sunlight.
However, Extremely low visible light transmittance or VLT can significantly reduce sunlight permeability leading to dark interiors. Consequently, dependency on artificial lights will increase, ultimately resulting in higher energy expenses.
To meet the energy target in the BASIX certificate, it is recommended that you purchase glass with optimal visible light transmittance.
Conductance
Signifies how easily and seamlessly a glass conducts heat or how a particular glass is susceptible to heat conduction. Conductance is generally denoted by the U value.
The U value and a glass's resistance to heat flow are inversely proportional. Therefore a glass with a low U value will have more efficient insulating properties, thus preventing heat loss from interiors and heat gain from exterior environment.
Solar Heat Gain Coefficient (Shgc)
The glass's solar heat gain coefficient (SHGC) quantifies how readily heat from direct sunlight flows through it. Typically SHGC is denoted as a number between 0 to 1.
A low glass SHGC ensures less solar heat is transmitted to the interior of the residential dwelling.
While some glass manufacturers consider SHGC depending on the type and design, the true SGHC value can only be calculated after considering the angle at which the solar radiation strikes the glass. Originally the wind orientation, shading, position of the Sun, season and time of the day needed to be taken into account for calculating actual SHGC.
All these glass properties are important considerations for commercial building sustainability evaluations such as DtS assessment and JV3 modelling.
Conclusion
Considering the correct class is important for achieving compliance in the energy section and thermal comfort section of the BASIX certificate.
