Yes, in most cases you can install a secondary glazing panel yourself — it's a popular, cost-effective way to improve thermal insulation and reduce condensation in older NZ homes. However, there are a few important things to check before you start, including building consent requirements, safety glazing rules, and whether your installation might affect Healthy Homes compliance if you're a landlord.
What Is Secondary Glazing?
Secondary glazing means adding a second layer of glazing to an existing window, creating a still-air gap that acts as insulation — similar in principle to double glazing, but without replacing the original window. It's especially common in older NZ homes with single-glazed timber joinery, where full window replacement can be expensive.
Secondary glazing systems typically come in a few forms:
- Rigid acrylic or polycarbonate panels fitted with magnetic or clip-on frames
- Flexible film kits (shrink-film applied with double-sided tape and a hairdryer)
- Sliding or hinged framed panels in aluminium or uPVC tracks
For a genuinely effective insulation upgrade, rigid panel systems with a proper air gap (ideally 20–100 mm) perform significantly better than thin film kits.
Do You Need a Building Consent?
This is the key question. Under Schedule 1 of the Building Act 2004, certain minor building work is exempt from requiring a building consent. Installing a secondary glazing panel that is not structural and does not affect the weathertightness of the building envelope is generally considered exempt work — but always confirm this with your local council before starting, as interpretations can vary.
You can read more about consent exemptions at MBIE Building Performance.
Safety Glazing Rules — Critical to Get Right
This is where many DIYers can get caught out. The NZ Building Code clause G12 and NZS 4223 set out requirements for glazing in certain locations — particularly in areas where people could fall through or where glass is within reach of children. If your secondary panel is in a critical location (such as low-level panels, near doors, or in bathrooms), the glazing material must meet safety standards.
Acrylic and polycarbonate panels used in most DIY secondary glazing kits are generally considered safer than glass in impact situations, but you should still check the product specifications and confirm compliance with your supplier. If you're using glass in a secondary glazing system, it must be safety glass (toughened or laminated) in critical locations.
When in doubt, consult a qualified glazier — you can find local glaziers on tradedirectory.co.nz.
Step-by-Step: Installing a DIY Rigid Panel System
Here's a general guide for a magnetic or clip-on acrylic panel kit, which are widely available at stores like Bunnings and Mitre 10.
What You'll Need
- Measuring tape and pencil
- Acrylic or polycarbonate panel (cut to size, or order pre-cut)
- Magnetic strip or clip-on frame kit
- Cleaning cloths and isopropyl alcohol
- Scissors or a sharp knife
Installation Steps
- Measure carefully — measure the window reveal (the recess inside the frame) width and height. Measure twice.
- Clean the window frame thoroughly with isopropyl alcohol so adhesive strips bond properly.
- Attach the magnetic or adhesive frame strips to the window reveal, following the manufacturer's instructions.
- Cut or fit the panel to size. Many suppliers will cut acrylic panels to your measurements.
- Press the panel into place and check for gaps around the edges — any gaps will reduce insulation performance significantly.
- Check for condensation over the following weeks. Some moisture between panes is normal initially, but persistent condensation may indicate an air leak.
Air Gap Size Matters
The insulating performance of secondary glazing depends heavily on the air gap between the existing window and the new panel. As a guide:
| Air Gap | Performance |
|---|---|
| Less than 10 mm | Minimal improvement |
| 20–50 mm | Good thermal improvement |
| 50–100 mm | Excellent thermal and acoustic improvement |
| Over 100 mm | Diminishing returns |
For more technical guidance on window insulation performance, BRANZ publishes research and guidance relevant to NZ conditions.
Healthy Homes Compliance for Landlords
If you're a landlord, note that the Healthy Homes Standards include glazing and insulation requirements. Secondary glazing may contribute to meeting these standards, but it's important to check the specific requirements at Tenancy Services to ensure your property is fully compliant.
Tips for Best Results
- Seal edges well — even small air gaps dramatically reduce effectiveness.
- Choose the right material — acrylic is lighter and easier to handle; polycarbonate is more impact-resistant.
- Consider ventilation — secondary glazing reduces airflow, so ensure rooms have adequate ventilation to prevent moisture build-up and mould.
- Removable panels are useful in summer — many magnetic systems allow easy removal.
When to Call a Professional
While basic secondary glazing panel installation is well within DIY reach, you should hire a qualified glazier if:
- You're unsure whether your installation location is a critical glazing zone under NZS 4223
- You want a framed sliding or hinged system that requires precise joinery work
- Your windows are large, awkward, or heritage-listed
- You want a professional finish or a system that adds value to your home
- You're a landlord needing documented compliance for Healthy Homes
A licensed glazier will ensure the work meets the NZ Building Code and can provide documentation if needed. Find a qualified local glazier through tradedirectory.co.nz.
Window & Glass Association
