Yes, in most cases a homeowner can install a second deadbolt on their own front door — it's not restricted work under NZ electrical, plumbing, or gas legislation. However, there are a few important things to consider before you reach for the drill: your door's construction, the NZ Building Code, and whether your tenancy or body corporate has any rules about alterations.
Why Add a Second Deadbolt?
A second deadbolt (also called a deadlock) adds a meaningful layer of security. A single latch or lockset can sometimes be defeated with a credit card or by manipulating the latch bolt, whereas a properly installed deadbolt throws a solid steel bolt deep into the door frame. Common reasons NZ homeowners add a second deadbolt include:
- Upgrading security after a break-in or near-miss
- Meeting insurance requirements (some insurers specify two locking points)
- Adding peace of mind in a rental property (check with your landlord first — tenants have rights around locks under the Tenancy Services Healthy Homes and rental rules)
- Replacing an ageing or low-quality existing lock without removing it
Choosing the Right Deadbolt
Not all deadbolts are equal. Look for these features when shopping at stores like Bunnings or Mitre 10:
- Grade/rating: Look for locks that meet or exceed Australian/New Zealand Standard AS/NZS 4145 for locksets — packaging will often state this.
- Bolt throw: A minimum 25 mm bolt throw is recommended; longer is better.
- Anti-pick, anti-drill, anti-bump: Look for these features on the cylinder.
- Keyed alike: If you want to use the same key as your existing lock, a locksmith can rekey the new deadbolt to match — very handy.
- Finish: Match the hardware finish (satin chrome, brushed nickel, etc.) to your existing lock for a tidy look.
Single-cylinder deadbolts (key outside, thumb-turn inside) are the most common choice for front doors. Double-cylinder deadbolts (key required on both sides) can be a fire-egress risk and are generally not recommended for main entry doors — in an emergency you need to be able to get out quickly without hunting for a key.
Checking Your Door First
Before drilling anything, assess your door:
| Door Type | Suitability | Notes |
|---|---|---|
| Solid timber | Excellent | Easy to drill, holds screws well |
| Hollow-core timber | Poor to fair | May not provide enough material for the bolt pocket |
| Aluminium-framed | Possible | Requires specialist bits; check frame thickness |
| uPVC/composite | Possible | Check manufacturer guidelines |
| Fire door | Caution | Modifications may void fire rating — seek advice |
Also check your door frame (jamb). The strike plate and its fixing screws are often the weakest point in a door — use 75–100 mm screws to fix the strike plate deep into the structural framing behind the jamb lining, not just the lining itself.
NZ Building Code Considerations
Adding a deadbolt to an existing door is generally considered maintenance or minor repair and does not require a building consent under Schedule 1 of the Building Act 2004. However, always confirm with your local council if you're unsure — rules can vary and your specific situation (e.g., a heritage building or apartment) may be different. You can find guidance at MBIE Building Performance.
If your front door is a fire-rated door (common in apartments or attached garages), any modification — including adding a lock — may affect its fire rating. Check with your body corporate, building manager, or a qualified tradesperson before proceeding.
How to Install a Second Deadbolt — Overview
This is a general guide only. Always follow the specific instructions supplied with your lock.
- Choose the position: Place the new deadbolt at least 200–300 mm above or below your existing lock, centred on the door stile. Avoid positioning it too close to the edge or to glass panels.
- Mark the hole centres: Use the template provided with the lock to mark the face bore (for the cylinder) and the edge bore (for the bolt mechanism).
- Drill the face bore: Typically 54 mm diameter — use a hole saw. Drill from both sides to avoid tear-out.
- Drill the edge bore: Typically 26 mm diameter — use a spade or auger bit, keeping it perfectly horizontal.
- Chisel the bolt recess: Mortise out a shallow recess so the bolt faceplate sits flush with the door edge.
- Fit the lock body and cylinder: Follow the manufacturer's instructions.
- Mark and fit the strike plate: Close the door, operate the bolt to mark the jamb, then chisel the recess and fix the strike plate with long screws into the structural framing.
- Test thoroughly: Make sure the bolt throws and retracts smoothly and the door closes properly.
When to Call a Professional
While deadbolt installation is DIY-friendly for a confident homeowner, consider calling a licensed locksmith if:
- You have an aluminium, composite, or fire-rated door
- Your door frame is damaged, rotten, or poorly aligned
- You want the new lock rekeyed to match your existing key
- You're unsure about the structural integrity of the frame
- You're a tenant and need the landlord's approval or a professional record of the work
- You simply want the job done right the first time
A qualified locksmith will also be able to assess your overall door security and recommend upgrades. You can find trusted local locksmiths on tradedirectory.co.nz.
Safety note: Adding locks is about security, but always ensure every occupant — including children and elderly family members — can exit the home quickly in an emergency. Never fit a double-cylinder deadbolt on a primary escape route.
