Glazing can have a major effect on BASIX compliance because windows influence how much heat a home gains, loses and retains. The size, orientation, frame type, glass type, shading and performance values of windows can all affect heating and cooling loads, which are central to the thermal comfort section of BASIX.
This is why glazing should not be treated as a late product selection. In many NSW residential projects, glazing needs to be coordinated with BASIX and NatHERS before approval. A window change that seems minor on the drawings can still affect thermal performance, especially if the project has large glazing areas, west-facing windows, limited shading or a tight 7 Star NatHERS outcome.
Glazing affects BASIX because windows influence heating loads, cooling loads and thermal comfort. BASIX and NatHERS may consider window size, orientation, U value, SHGC, frame type, glass type and shading. If glazing changes after the certificate is issued, the BASIX Certificate may need to be checked or amended.
BASIX covers water, energy use and thermal performance for NSW residential development. The thermal performance section is where glazing often becomes especially important. Windows can affect how much heat enters the home in summer and how much heat escapes in winter, which can influence the heating and cooling loads used in the assessment.
The NSW Planning Portal explains that BASIX window inputs can include frame and glass types, and that the BASIX Certificate shows the maximum allowable U value and acceptable SHGC range for selected frame and glass types. This means the chosen glazing can become a real certificate commitment, not just a design preference.
U value measures how readily heat passes through a window. In BASIX, U value refers to the total product U value, which means the glass and frame together. A lower U value indicates better insulation because less heat flows through the window.
For heating loads, a lower U value can help reduce heat loss in winter. For cooling loads, a lower U value can also help reduce conducted heat gain when it is hotter outside than inside. This is why windows with better insulating performance can support stronger thermal comfort outcomes.
SHGC stands for Solar Heat Gain Coefficient. It measures how much solar heat enters through the window. A higher SHGC allows more solar heat into the home. A lower SHGC reduces solar heat gain.
Neither high nor low SHGC is automatically best in every situation. A higher SHGC can help with winter solar gain, but it may increase cooling loads. A lower SHGC can help reduce summer heat gain, but it may also reduce useful winter warmth. The right choice depends on orientation, shading, climate and the overall design.
The same window can perform differently depending on its orientation. North-facing glazing can often be managed with appropriate shading to allow winter sun and reduce summer heat. West-facing and east-facing glazing can be more difficult because low angle sun can create strong heat gain that is harder to shade effectively.
NSW Planning’s BASIX guidance notes that reducing the area of windows facing west, east and northwest can help reduce cooling load. It also explains that BASIX uses window orientation sectors based on True North, not Magnetic North. This means the north point and window orientation need to be accurate in the plans used for assessment.
Shading is one of the main ways to manage solar heat gain through windows. Eaves, awnings, balconies, pergolas, external louvres and neighbouring overshadowing can all affect how much sun reaches the glass. In BASIX and NatHERS, shading can influence the balance between reducing cooling loads and allowing useful winter solar access.
NSW Planning explains that adjustable shading can reduce cooling load while keeping heating load at the same level because BASIX assumes adjustable shading is used in summer and drawn back in winter to permit solar gain. It also notes that internal louvres or blinds are not recognised in BASIX, which means external or recognised shading needs to be considered carefully.
Large windows can support daylight, views and connection to outdoor areas, but they can also increase thermal risk. A large window on a difficult orientation may increase cooling loads. A large window with poor insulating performance may increase heat loss in winter. The impact depends on the whole design, not only the glass area.
A project can still have generous glazing, but the glazing strategy should be considered early. Better window performance, correct shading, reduced west-facing glass, improved insulation and careful orientation can all help the project reach the required BASIX and NatHERS outcome without unnecessary redesign.
To assess glazing properly, the assessor needs enough information to understand the windows and glazed doors shown on the plans. If a formal window schedule is available, it can be very helpful. If not, the assessor may begin with the sizes and locations shown on the floor plans and elevations, but final glazing details may still need to be confirmed before the certificate is issued.
Useful glazing information includes:
Yes. Changing windows can affect a BASIX Certificate. This includes changes to window size, location, orientation, frame type, glass type, U value, SHGC or shading. A window change may also affect NatHERS thermal comfort modelling if the project uses the simulation method.
If windows change after a BASIX Certificate has been issued, the certificate should be checked before the updated plans are lodged, certified or built. Some changes may have little effect, while others may require the assessment to be updated or the design to be adjusted.
Glazing issues often delay BASIX because window details are sometimes left unresolved until late in the design process. Common issues include:
The best glazing strategy depends on the home, climate, orientation and design intent. However, common improvement options include:
Certified Energy prepares BASIX Certificates and NatHERS assessments for NSW residential projects. Our team can review the glazing strategy, window schedule, shading, insulation and thermal comfort pathway before the certificate is finalised.
This is especially useful for custom homes, renovations, secondary dwellings, dual occupancies, townhouses and multi dwelling developments where glazing has a strong effect on thermal comfort and approval documentation.
Send your plans or window schedule to Certified Energy and our team can review how glazing may affect BASIX and NatHERS outcomes.
Request a ReviewGlazing affects BASIX compliance because windows influence heating loads, cooling loads and thermal comfort. The size, orientation, frame type, glass type, U value, SHGC and shading of windows can all affect whether a project meets the BASIX thermal performance requirements.
U value measures the ability of the whole window, including glass and frame, to conduct heat. A lower U value means the window is a better insulator and can reduce heat flow through the window.
SHGC stands for Solar Heat Gain Coefficient. It measures how much solar heat enters through the window. A lower SHGC reduces solar heat gain, which can help with cooling loads, while a higher SHGC can allow more winter solar gain but may increase cooling loads.
Yes. Changing window sizes, locations, frame types, glass types, U values, SHGC values or shading can affect BASIX and NatHERS outcomes. If windows change after a BASIX Certificate is issued, the certificate should be checked before relying on it.