A Cost Benefit Analysis of Secondary Glazing as a Retrofit Alternative for New Zealand Homes

Homes with single glazing represent a large majority of the New Zealand housing stock. With the recent changes to the NZ Building Code Clause H1 Energy Efficiency, new homes require higher glazing thermal performance. This will lead to an increased need for cost effective methods to improve window thermal performance in existing single glazed homes without completely replacing the windows, which includes 'secondary' glazing. There are several secondary glazing options available including 'stick-on' plastic glazing as well as aluminium framed glass solutions that are installed inside the existing joinery. Secondary glazing is marketed as a cost effective alternative to insulated glazing units, providing both improved acoustic and thermal insulation to existing windows. There is little information regarding the in-use performance and cost benefits of secondary glazing in New Zealand. This thesis explores the efficacy of the secondary glazing products when installed in existing single pane frames. A guarded hotbox was used to make thermal resistance measurements on a typical single glazed aluminium window with timber reveal liner. Four common secondary glazing systems were retrofitted into the window - (1) thin plastic film; (2) magnetically-attached acrylic sheet; (3) aluminium framed secondary glazing; and (4) aluminium framed low emissivity (low-E) secondary glazing. Models of 'typical' New Zealand homes created in the ALF building thermal simulation programme were used to explore the heating energy savings and cost benefits provided by the different secondary glazing systems in a range of locations. Of the tested products, the low-E secondary glazing produces the largest cost-benefits. At current energy and material costs, secondary glazing was found to not be a financially viable solution in warmer climates such as Auckland. In cooler climates such as Christchurch and Dunedin, secondary glazing was found to be a cost effective retrofit alternative for existing single glazed homes