Retrofit vs full frame double glazing: retrofit fits new glass into existing frames, while full frame replaces the whole window. Which suits your home?
Retrofit double glazing keeps your existing frames and fits a new double-glazed unit or secondary pane into them, which is usually cheaper and quicker. Full frame replacement removes the whole window and installs new joinery, which costs more but suits frames that are damaged, warped or not thermally broken. Frame condition should drive the decision.
Choosing retrofit vs full frame double glazing is one of the first decisions once you decide to upgrade an older New Zealand home, since single glazing is usually the weakest point for heat loss, condensation and noise.
Both are established options, not a budget-versus-premium choice. Here is how to work out which one suits your home.
Full frame replacement removes the entire window unit, frame included, and installs new double-glazed aluminium, timber or uPVC joinery. It is the more disruptive and expensive option, but it resets the whole window, not just the glass.
Retrofit, sometimes called secondary glazing, keeps your existing frame and either swaps the single pane for a double-glazed unit or adds a second glazed panel alongside it. The work is quicker and keeps the original joinery.
Retrofit works best when the existing frames are in good condition and built deep enough to take the new glass.
If frames are damaged, warped or simply not built to accept a retrofit unit, replacement is usually the only real option. It is also worth considering if you are already renovating and want new joinery to match, or if your current frames are not thermally broken.
A thermal break is a low-conductivity barrier between the inner and outer parts of an aluminium frame. Without one, heat moves straight through the metal and the frame can stay cold enough to attract condensation, undermining the benefit of better glass.
Clause H1 of the Building Code raised the minimum thermal performance for windows in stages. According to BRANZ, minimum window R-values rose to R0.37 from November 2022, then to R0.46 in the milder climate zones and R0.50 in the coldest from May 2023, with zones 1 and 2 following at R0.46 in November 2023. Check the current H1 documents for exact zone figures.
The practical point: ask any installer for the tested R-value of the specific window or retrofit system they are quoting, rather than accepting a general claim that it is better than single glazing. Also ask whether safety glass is required for low windows and glazed doors.
The Energy Efficiency and Conservation Authority's Warmer Kiwi Homes programme funds ceiling and underfloor insulation and approved heaters, as its announcements describe. Double glazing is not among the items it funds, so budget for the full cost of either approach and check EECA for current eligibility.
Get quotes for both approaches, because the better option depends on the condition of your frames, not a fixed rule. Ask the installer to inspect your frames in person, and get warranty terms for both the glass unit and the installation in writing.
The Window and Glass Association of New Zealand (WGANZ) is the industry body. Membership is voluntary, so ask whether a business is a member and confirm it on the association's own site. For a shortlist, our Top 5 double glazing installers lists check each business against the NZ Companies Office and NZBN register, Google Business Profile evidence, relevant industry registers and reviews, and exclude lead-generation sites and unverified operators.
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For frames in sound condition, retrofit can close much of the performance gap at lower cost and with less disruption. It is not right for every home, particularly where frames are damaged or not thermally broken. Ask for the tested R-value of what is quoted.
Retrofit is usually cheaper per window because the frame stays, while full replacement includes new joinery. Price depends on the number and size of windows, frame material, glass specification, gas fill and location, so get quotes from two or three installers.
Often yes, if the timber is sound and the frame can take the unit. Retrofit is a common choice for character homes where the original joinery is worth keeping, but an installer must inspect the frames first.
Not through Warmer Kiwi Homes, which funds insulation and heaters rather than glazing. Check EECA's current programme details, because eligibility changes over time.
Ask whether your frames suit retrofit or need replacement, ask for tested performance figures, check whether they belong to an industry body such as WGANZ, and get warranty terms for the glass and the installation in writing.
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