A broken window pane is one of those jobs that can look deceptively simple — but depending on the type of glass, the window location, and the size of the pane, it can quickly move beyond a straightforward DIY fix. Here's what you need to know before you pick up a glass cutter.
Is It Legal for a Homeowner to Replace Glass in NZ?
In New Zealand, there is no specific licensing requirement that prevents a homeowner from replacing a simple single-glazed pane in a timber-framed window on their own property. However, there are important caveats:
- Safety glass is required by the NZ Building Code in certain locations — including doors, sidelights, low-level glazing (generally below 1 metre from the floor), bathrooms, and around staircases. Using the wrong type of glass in these areas is a Building Code breach.
- If the work involves structural changes to the window frame or opening, a building consent may be required. Check with your local council or visit MBIE Building Performance for guidance.
- Replacing glass in commercial buildings or rental properties (especially under Healthy Homes obligations) may have additional requirements.
If you're unsure whether your situation requires a professional, it's always worth a quick call to a licensed glazier — you can find one on tradedirectory.co.nz.
What Type of Glass Do You Need?
Choosing the right glass is critical for both safety and compliance. Common types include:
| Glass Type | Common Use | NZ Building Code Required? |
|---|---|---|
| Standard float glass | General windows, high-level glazing | No (where safety glass not required) |
| Toughened (tempered) safety glass | Doors, low-level glazing, wet areas | Yes, in specified locations |
| Laminated safety glass | Overhead glazing, high-risk areas | Yes, in specified locations |
| Double glazing (IGU) | Energy efficiency, modern homes | Specialist installation required |
Safety glass (toughened or laminated) is required under NZS 4223 in any location where a person could fall into or through the glass. BRANZ has useful guidance on glazing requirements for NZ homes. When in doubt, always upgrade to safety glass — it's not significantly more expensive for small panes and could save a life.
Tools and Materials You'll Need
For a basic single-glazed timber window replacement, you'll typically need:
- Replacement glass cut to size (most glass suppliers and hardware stores like Mitre 10 or Bunnings can cut glass to order)
- Heavy-duty gloves and safety glasses
- Putty knife and glazing chisel
- Linseed oil putty or modern glazing compound
- Glazing sprigs (small metal pins) or glazing clips
- Tape measure and pencil
- Primer (for bare timber rebates)
Measure the rebate opening carefully — cut your glass approximately 2–3 mm smaller than the opening on each dimension to allow for expansion and fitting tolerance.
Step-by-Step: Replacing a Single-Glazed Pane in a Timber Frame
1. Remove the broken glass safely
Wear thick gloves and eye protection. Score around the old putty with a putty knife, then carefully remove glass fragments. Dispose of broken glass wrapped in newspaper inside a cardboard box — never loose in a rubbish bag.
2. Clean out the rebate
Chisel out all old putty and remove glazing sprigs. Sand the rebate smooth and apply a coat of primer or linseed oil to bare timber — this prevents the new putty from drying out too quickly.
3. Bed the new glass
Press a thin layer of putty (the "back putty") into the rebate, then carefully press the new glass pane into place. Secure with glazing sprigs tapped gently into the frame every 200–250 mm.
4. Apply face putty
Apply putty around the front edge of the glass, angling it neatly with a putty knife to form a clean bevel. Smooth with a wet finger or knife dipped in water.
5. Paint and finish
Allow putty to skin over (usually a week or so) before painting. The paint should overlap slightly onto the glass to seal the putty edge and prevent moisture ingress.
Aluminium and uPVC Frames
Replacing glass in aluminium or uPVC frames is more complex. These frames use rubber gaskets and beading rather than putty, and the beading must be carefully removed and refitted without cracking. Double-glazed units (IGUs) cannot be reglazed in the field — the entire sealed unit must be replaced. This work is best left to a professional glazier.
When to Call a Professional
You should always call a licensed glazier if:
- The pane is larger than about 0.5 m² — large panes are heavy and awkward to handle safely
- The window is in a safety glass location and you're unsure of the correct specification
- The frame is aluminium, uPVC, or steel
- The window is double-glazed (IGU replacement required)
- The window is above ground level and requires working at height
- There is frame damage alongside the broken glass
- The property is a rental and you need to meet Tenancy Services Healthy Homes standards
A qualified glazier will also be able to certify that safety glass has been correctly installed — important for insurance and resale purposes. Find a trusted local glazier on tradedirectory.co.nz.
Safety First
Glass injuries can be serious. Always wear cut-resistant gloves and eye protection when handling glass. Never attempt to carry a large pane alone. If a pane has shattered into your home, ventilate the area and vacuum carefully — tiny glass fragments can travel further than you'd expect.