Window Standardisation - The Potential in New Zealand

This report investigates the potential benefits of, and obstacles to, standardising window sizes in New Zealand's residential building industry. The argument can be made that traditional on-site construction dominates the NZ residential building sector. Houses are often custom-designed, with cost being the primary concern for homeowners. The argument continues that low productivity and fragmentation plague the industry, hindering efficiency. Prefabrication and DfMA (Design for Manufacture and Assembly) is argued as offering a potential solution. Standardisation of windows is then seen as a crucial part of achieving efficiency gains through these methods. A systematic literature review confirmed that much of the published research in the field focuses on the vital role of windows as building components affecting energy consumption and occupant comfort. Window size (through Window to Wall Ratio) and thermal performance (thermal conductivity and Solar Heat Gain performance) influence energy use. What was missing from the publications that were found was papers addressing: • How window size standardisation might impact energy efficiency in houses. • Cost analyses comparing bespoke vs. standardised window manufacturing. • Potential obstacles to implementing window standardisation in the industry. • Potential benefits of window standardisation beyond cost reduction. These were the focus of the 9 industry interviews. The interviewees were suggested by the Window Glazing Manufacturers’ Association (6) and the Frame and Truss Manufacturers' Association (3). Overall, the industry was divided on the potential benefits and drawbacks of window standardisation. While there is possibly some potential for cost savings and other benefits, significant obstacles remain, including the deeply ingrained culture of customization in New Zealand’s construction industry. It seems likely that cost savings from standardisation will only be realised if the whole residential construction process is standardised. In summary, the industry interview key findings were: • Limited Cost Savings: Industry experts believe that window standardisation would offer minimal cost savings in fabrication due to current manufacturing processes. • Limited Time Savings: Standardised windows wouldn't necessarily lead to faster project completion as bespoke windows can be readily manufactured upon order. • Over-specification: Standardised windows could be designed with unnecessary features, increasing costs for applications where they aren't required. • Under-specification: Standardised windows might not meet specific needs, leading to safety hazards or performance issues. • Flexibility: Bespoke windows allow for customisation to meet specific design and performance requirements. An analysis of building permit data for 276 houses revealed a high diversity in window sizes, with no clear dominant dimensions. While some window widths seem influenced by common stud spacings (0.4m and 0.6m), a significant portion of windows have dimensions outside these ranges. The report suggests that, in the view of the industry, window standardisation in New Zealand’s residential construction may not offer significant cost or time savings. Additionally, industry suggests that drawbacks like over-specification and a potential loss of design flexibility could outweigh potential benefits. The data analysis supports this conclusion, revealing a highly diverse window size landscape in New Zealand construction. No literature could be sourced that provided data on potential cost savings from standardising windows in residential building construction. It does seem possible that standardised windows could be beneficial in a future scenario where the whole residential construction process was standardised.