Home Forums General Discussion Secondary Glazing Reply To: Secondary Glazing

Norman Smith

Hi Nik, this is an area which has been subject to considerable research and would be available in the literature in topics fields such as WERS – window energy rating schemes. Sites such as ashttp://windows.lbl.gov/adv_Sys/hi_R_insert/GapWidths.html offer an introduction to the subject – Optimal gap width for double and triple glazing systems.


Here in NZ I found the report referenced below highly relevant, not the least because it demonstrates to households that (shock horror) the DIY retrofit film double glazing performs as well as, and sometimes better, that some ‘proper’ DG at a fraction of the cost. I can make this report available to anyone who is interested, also speak from my own experience.

This rasies the issue around how to resource topic areas when more information is required than available within the Hub. Some years back I was funded by the electricity sector to provide an information service to answer “all” questions by members of the public. In the case of such an enquiry as this I believe a combination of desk-based research and talking to people at BRANZ and others would be required to provide a reasonable answer, and that would take me at least an hour.

Cheers, Norman

SB10 Conference Paper Number: 60
Scientific Paper, Student Paper
Houses 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 houses 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 houses without completely replacing
the windows.
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 paper will explore the
efficacy of the secondary glazing products when installed in existing single pane frames.
A guarded hotbox was used to make thermal transmittance measurements on a typical single glazed
aluminium window. 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 houses 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. 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 households.