Yes, replacing an existing deadbolt lock on a wooden door is well within the reach of most DIY-minded homeowners. As long as you're swapping a deadbolt for a like-for-like replacement (same or similar backset and bore size), no specialist tools or licensed trades are required. If you need to cut new holes or significantly modify the door, it gets trickier — but still doable with the right gear.
What You'll Need
Before you start, gather the following:
- Flathead and Phillips-head screwdrivers (a power drill/driver speeds things up)
- Tape measure and pencil
- Sharp chisel and mallet (for adjusting the strike plate recess if needed)
- Hole saw kit (only if cutting new bores — typically 54 mm for the cylinder and 25 mm for the latch)
- New deadbolt lock set — available from Bunnings or Mitre 10
- Wood filler or epoxy (optional, for filling old screw holes)
Understanding Deadbolt Sizing
The two key measurements are the backset (distance from the door edge to the centre of the cylinder hole) and the bore diameter (the hole the lock body sits in). In NZ, the most common backsets are 60 mm and 70 mm. Check your existing lock before buying a replacement — most lock packaging will state which backsets it suits.
Also check the door thickness. Standard NZ interior and exterior timber doors are typically 35–45 mm thick. Most deadbolt sets accommodate this range, but confirm on the packaging.
Step-by-Step: Replacing an Existing Deadbolt
1. Remove the old lock
- Open the door and unscrew the interior thumb-turn plate (usually two screws).
- Pull both halves of the lock cylinder apart and slide out the latch bolt assembly from the door edge.
- Unscrew and remove the old strike plate from the door frame.
2. Check the bore and backset
- Measure the existing holes and compare with your new lock's requirements.
- If the holes match, you're in luck — fitting is straightforward.
- If the new lock has a slightly different backset, you may need to chisel the latch plate recess a little deeper or fill and re-drill (see below).
3. Fit the new latch bolt
- Slide the new latch bolt into the door edge hole, with the angled face of the bolt pointing toward the door frame (so it compresses as the door closes).
- Mark and chisel the recess so the latch plate sits flush with the door edge. A flush fit is important — a proud plate can prevent the door from closing properly.
- Screw the latch plate in firmly.
4. Install the cylinder and thumb-turn
- Feed the connecting bar (cam or tailpiece) through the latch mechanism.
- Fit the exterior cylinder and interior thumb-turn, aligning the screw holes.
- Tighten the connecting screws — snug but not so tight the cylinder binds.
5. Fit the strike plate
- Close the door slowly and mark where the latch bolt meets the frame.
- Hold the strike plate in position, mark the recess, and chisel it out so the plate sits flush.
- For added security, use long screws (75–100 mm) to fix the strike plate through the door frame and into the structural framing behind — this significantly improves kick-in resistance.
- Test the lock several times with the door open before closing it fully.
Installing a Deadbolt in a New Location
If there's no existing hole, you'll need a hole saw (typically 54 mm diameter) and a drill. Mark the centre point at the standard height (around 1000–1200 mm from the floor is common, but there's no fixed NZ code requirement for residential deadbolts). Drill from both sides of the door to avoid tear-out. Then chisel the latch pocket in the door edge with a 25 mm spade bit and chisel.
This is still DIY-friendly, but take your time — mistakes on a door edge are harder to fix than on a flat surface.
Security Tips Worth Knowing
- Choose a deadbolt that meets Grade 1 or Grade 2 security ratings (look for ANSI/BHMA grading on the packaging, which is commonly referenced in NZ retail).
- Anti-pick, anti-drill, and anti-bump features are worth paying for on an exterior door.
- If you're a landlord, be aware that under the Healthy Homes Standards, rental properties must have functioning locks on all exterior doors and windows. Replacing a faulty deadbolt is part of your obligations.
- Avoid leaving the door on the latch while you work — prop it open safely so you don't lock yourself out.
When to Call a Professional
Deadbolt replacement is not restricted work under NZ law — unlike electrical or gas work, there's no licensing requirement. However, call a qualified locksmith if:
- The door frame or door itself is damaged, warped, or rotten (a lock is only as strong as what it's fitted to).
- You need a master key system or high-security lock rekeyed to match existing keys.
- The lock has been forced or tampered with and you're unsure of the extent of damage.
- You're fitting locks to a commercial premises or a multi-unit building where security standards may be higher.
- You simply don't feel confident — a poor installation can compromise your home's security.
A qualified locksmith can also advise on the best lock grade for your situation. You can find licensed local locksmiths on tradedirectory.co.nz.
