Replacing a broken fanlight window above an exterior door is something many confident DIYers can tackle, provided the frame is undamaged and the glass size is straightforward. The key steps are removing the old glass safely, measuring accurately, ordering the correct replacement glass, and re-glazing with proper weatherproofing — all important in New Zealand's variable climate.
Safety First
Broken glass is extremely hazardous. Before you start, put on heavy-duty leather gloves, safety glasses, and closed-toe shoes. Lay a drop sheet below the fanlight to catch any falling shards. If the fanlight is at height and you need a ladder, make sure it is stable and ideally have a second person to assist. Check WorkSafe NZ for general safe working-at-height guidelines.
If the glass is laminated, toughened (tempered), or double-glazed, take extra care — toughened glass shatters into many small pieces, and double-glazed units contain a sealed air or gas gap that cannot be repaired on-site. These units must be replaced as a complete sealed unit.
What Type of Glass Do You Have?
Fanlights above exterior doors in NZ homes are commonly glazed with:
- Single-pane float glass — older homes, straightforward to replace
- Toughened (safety) glass — required by the NZ Building Code in certain locations near doors (check NZS 4223 and the MBIE Building Performance guidance on safety glazing)
- Double-glazed units (IGUs) — increasingly common in modern and renovated homes
- Obscure or patterned glass — for privacy; must be matched in style
Under the NZ Building Code, glazing in critical locations — including panels within certain distances of a door and below certain heights from the floor — must meet safety glazing requirements. A fanlight directly above a door may or may not fall into a critical location depending on its height; if in doubt, check with your local council or a licensed glazier.
Tools and Materials You'll Need
- Heavy-duty gloves and safety glasses
- Glazier's hacking knife or old chisel
- Putty knife and stiff scraper
- Tape measure and straight edge
- Replacement glass (cut to size by your glass supplier)
- Glazing putty (for timber frames) or glazing tape/silicone (for aluminium frames)
- Glazing sprigs or clips (for timber frames)
- Paintable exterior primer and paint (if re-puttying timber)
- Mild detergent and clean cloths
Step-by-Step: Removing the Broken Glass
- Tape the glass with masking tape in a cross pattern before removal — this helps hold loose shards together.
- Carefully remove any glazing beads (the thin strips of timber or aluminium holding the glass in). Timber beads are usually pinned; aluminium beads often clip or screw in place.
- Gently work the broken glass free, starting from one corner. Place all shards immediately into a cardboard box or thick rubbish bag — never loose in a bin.
- Remove old putty or sealant from the rebate using a hacking knife or chisel. For aluminium frames, clean out old glazing tape or silicone thoroughly.
- Clean the rebate with a damp cloth and allow it to dry completely.
Measuring for Replacement Glass
Measure the rebate opening (the inside of the frame where the glass sits) in at least two places — width and height — as old frames are rarely perfectly square. Deduct 3–4 mm from each dimension to allow for expansion and fitting tolerance. Write down your measurements and take them to your glass supplier.
For double-glazed units, the supplier will need the overall unit size, spacer bar width, and glass type. These are made to order and typically take a few days.
Local glass suppliers and glaziers can cut glass to size. You can also find glazing supplies at Mitre 10 or Bunnings for standard single-pane work.
Fitting the New Glass
Timber Frames (Putty Glazing)
- Apply a thin bed of linseed oil putty around the rebate (the back bedding coat).
- Press the new glass firmly into the putty, centring it in the opening.
- Secure with glazing sprigs tapped in every 150–200 mm using a pin hammer.
- Apply the face putty at a 45° angle, smoothing it neatly with a wetted putty knife.
- Once the putty has skinned over (usually 1–2 weeks), prime and paint to seal it from the weather — unpainted putty will crack and fail.
Aluminium Frames (Bead Glazing)
- Apply glazing tape or a bead of neutral-cure silicone around the rebate.
- Press the glass into position.
- Refit the glazing beads, clipping or screwing them back into place.
- Run a neat bead of exterior-grade silicone along any exposed joints to weatherproof. Sika and other brands offer suitable neutral-cure silicone for glazing.
Weatherproofing and the NZ Climate
New Zealand's climate — particularly in coastal and high-rainfall regions — demands good weatherproofing around any glazing. Make sure all joints are fully sealed, and check that the fanlight frame itself has no rot, corrosion, or failed sealant at its junction with the door frame. Poor sealing can lead to moisture ingress and issues under NZ Building Code Clause E2 (External Moisture).
Does This Work Need a Building Consent?
Replacing glass in an existing frame on a like-for-like basis is generally exempt from building consent under Schedule 1 of the Building Act. However, if you are changing the frame, altering the opening, or upgrading to a different glazing system, you may need consent. Always confirm with your local council before starting. See MBIE Building Performance for Schedule 1 guidance.
When to Call a Professional
Call a licensed glazier if:
- The fanlight frame is damaged, rotten, or corroded and needs repair or replacement
- The glass is in a safety glazing critical location and you are unsure of the correct specification
- You need double-glazed units made and fitted
- The fanlight is at significant height and safe access is difficult
- You are not confident working with glass safely
A qualified glazier will ensure the correct glass type is used, the installation meets the NZ Building Code, and the work is properly weatherproofed. You can find experienced local glaziers on tradedirectory.co.nz.
Window & Glass Association
