Yes, installing a new interior door frame is one of the more approachable DIY joinery tasks — no building consent is typically required for a straight replacement, and no licensed trade is legally restricted from doing this work. That said, getting a neat, square, and functional result does take patience, the right tools, and a willingness to measure twice (and cut once). If you're a first-timer, read on before you pick up a hammer.
What the Job Actually Involves
An interior door frame (also called a door lining or door casing) consists of two vertical jambs and a horizontal head jamb that line the rough opening in the wall. On top of that, architrave trim is fixed to both sides to cover the gap between the frame and the wall lining. The door itself then hangs from hinges mortised into one jamb.
For a straight swap — removing an old frame and fitting a new one in the same opening — the job is DIY-friendly. If you're creating a new opening in a wall, things get more complex (see below).
Tools and Materials You'll Need
- Tape measure, combination square, and spirit level — accuracy is everything
- Handsaw or mitre saw — a mitre saw makes cleaner cuts and is worth hiring if you don't own one
- Hammer and nail punch, or a brad nailer
- Chisel and mallet — for hinge mortises
- Pry bar — for removing the old frame
- Pencil, shims (timber wedges), and gap filler
- Door frame kit or pre-machined timber (pine or MDF, typically 90 mm or 140 mm wide depending on your wall thickness)
- Architrave to match your existing interior style
- Screws, nails, and construction adhesive
You'll find door frame kits and pre-primed architrave at Bunnings, Mitre 10, and PlaceMakers.
Step-by-Step Overview
1. Remove the Old Frame
Use a pry bar to carefully remove the architrave from both sides, then work the jambs free. Take care not to damage the surrounding wall lining — GIB plasterboard is easy to crack if you're heavy-handed.
2. Check and Prepare the Rough Opening
Once the old frame is out, check the rough opening with a spirit level and square. The head should be level and the sides plumb. Note the exact width and height so you can cut your new jambs to length.
3. Cut the Jambs and Head
Cut your two side jambs to the correct height. The head jamb sits between them, so its length equals the door width plus the thickness of both jambs. Use a mitre saw for clean, square cuts.
4. Assemble and Fit the Frame
Join the head to the jambs with screws or nails. Offer the assembled frame into the opening and use timber shims to adjust it until it's perfectly plumb and level. Check the diagonal measurements — they should be equal, confirming the frame is square. Fix through the jambs and shims into the surrounding framing.
5. Hang the Door
Mark and mortise the hinge positions on the hinge jamb (typically 150 mm from the top and 225 mm from the bottom for standard hinges, with a third hinge in the middle for heavier doors). Chisel out the recesses so hinges sit flush. Fit the door and check it swings freely and latches correctly.
6. Fix the Architrave
Mitre the architrave at 45° at the corners and nail it to the jambs and wall framing. Leave a small reveal (typically 6–8 mm) between the inside edge of the jamb and the architrave. Fill nail holes, sand, and paint or prime ready for finishing.
Key Things That Can Go Wrong
| Problem | Likely Cause | Fix |
|---|---|---|
| Door won't close properly | Frame not plumb or square | Re-shim and re-check diagonals |
| Gaps between frame and wall | Rough opening too wide | Pack with additional shims or filler |
| Architrave won't sit flat | Wall lining uneven | Sand high spots or use flexible gap filler |
| Door binds on the latch side | Hinge mortises too deep | Pack hinges with cardboard |
Do You Need a Building Consent?
Replacing a like-for-like interior door frame in an existing opening is generally exempt from building consent under Schedule 1 of the Building Act 2004. However, if you're cutting a new opening in a wall — especially a load-bearing wall — that's a different matter entirely and will almost certainly require consent and the involvement of a Licensed Building Practitioner (LBP). Always confirm with your local council before starting any structural work. You can find more guidance at MBIE Building Performance.
Finishing and Painting
Once the frame is fitted, prime any bare timber before painting. Resene, Dulux, and Wattyl all offer interior trim paints and primers suited to door frames and architrave. Two coats of a semi-gloss or gloss finish is standard for interior joinery — it's durable and easy to wipe clean.
When to Call a Professional
Consider hiring a qualified joiner or carpenter if:
- You're creating a new opening, particularly in a load-bearing wall
- The existing rough opening is badly out of square or damaged
- You want a pre-hung door fitted precisely (especially for fire doors or acoustic doors)
- You're not confident with a mitre saw or chisel work
- The job involves electrical wiring or plumbing near the opening — that work must be done by a licensed electrician (EWRB) or plumber (PGDB) respectively
A skilled joiner will get the job done quickly and with a professional finish. You can find qualified local joiners and carpenters on tradedirectory.co.nz.
