Fitting a joist hanger into a notched bearer is a common deck-framing technique in New Zealand, and when done correctly it keeps your deck joists flush with the top of the bearer for a neat, strong result. The key is accurate marking, clean cuts, and using the manufacturer-specified fixings — shortcuts here can compromise the structural integrity of your deck.
What Is a Notched Bearer and Why Do It?
A notched bearer (sometimes called a rebated or housed bearer) has a rectangular recess cut into its top edge so that a joist hanger sits flush or semi-flush, allowing the joist top to sit level with the bearer top. This is common on deck perimeter beams and mid-span bearers where you want a flat, even deck surface without a step-down at the bearer.
The alternative — face-fixing hangers to the side of a bearer — is simpler but results in joists sitting lower than the bearer top, which can cause drainage and trip-hazard issues on decks.
Tools and Materials You'll Need
- Tape measure, pencil, and square
- Circular saw or handsaw
- Sharp chisel and mallet
- Drill and appropriate drill bits
- Joist hangers (sized to match your joist dimensions)
- Manufacturer-specified joist hanger nails or screws (typically 30–40 mm galvanised or stainless)
- Safety glasses and hearing protection
Timber note: All structural deck timber in NZ should be H3.2 treated (above ground, exposed) or H4 where in contact with the ground or concrete, in accordance with MBIE Building Performance guidelines and NZS 3604.
Step-by-Step: Notching the Bearer
1. Select and Position Your Joist Hanger
Choose a hanger sized to match your joist width and depth exactly. Common NZ deck joists are 190 × 45 mm or 140 × 45 mm H3.2 treated pine. Hold the hanger against the bearer in the correct position and use it as a template — this is more accurate than measuring alone.
2. Mark the Notch
With the hanger held in place, mark the width and depth of the notch clearly on the bearer with a pencil and square. The notch depth is typically equal to the flange height of the hanger (often 40–50 mm), so the hanger sits flush or just below the bearer's top surface. Double-check your marks are square — an out-of-square notch will cause the joist to twist.
3. Make the Cuts
Set your circular saw blade to the exact notch depth — no deeper. Make two parallel cuts for the sides of the notch, then make several relief cuts across the waste area to make chiselling easier. Never cut deeper than required, as over-cutting weakens the bearer.
Finish with a sharp chisel and mallet, working with the grain to clean out the waste timber. Check the hanger fits snugly — it should sit flat with no rocking.
4. Check Bearer Integrity
The notch must not remove more timber than the bearer can structurally afford to lose. As a general rule, notches in the top of a bearer should not exceed one-third of the bearer depth. If you're unsure whether your bearer size can accommodate the notch, consult a Licensed Building Practitioner (LBP) or structural engineer. Refer to NZS 3604 for prescriptive timber framing rules, or check with your local council.
5. Install the Joist Hanger
Drop the hanger into the notch. Fix it using only the nails or screws specified by the hanger manufacturer — using the wrong fixings (e.g., standard wire nails instead of joist hanger nails) can significantly reduce the hanger's rated load capacity. Fill every fixing hole in the hanger; leaving holes empty reduces strength.
Popular hanger brands available in NZ include Simpson Strong-Tie and Pryda, both stocked at Bunnings and Mitre 10. Always check the manufacturer's load tables to confirm the hanger suits your joist span and load.
6. Install the Joist
Slide the joist into the hanger and fix through the hanger's joist holes into the joist. Check the joist is plumb and level before fully fixing off.
Galvanising and Corrosion Requirements
In NZ's coastal and high-humidity environments, stainless steel or hot-dip galvanised hangers and fixings are strongly recommended — and in some cases required by the Building Code. Using plain steel fixings with treated timber accelerates corrosion. Check the hanger manufacturer's specifications and BRANZ guidance for corrosion zone requirements.
Does This Work Need a Building Consent?
Deck construction in NZ often requires a building consent, depending on the deck's height, size, and proximity to boundaries. Some low decks may qualify as Schedule 1 exempt work under the Building Act, but this is not automatic — always confirm with your local council before starting. Structural work that does not comply with the Building Code can create problems when you sell your home. See MBIE Building Performance for guidance on consent exemptions.
When to Call a Professional
If your deck is more than 1 metre above ground, is attached to the house, or involves any structural modifications to existing framing, it's strongly advisable to engage a Licensed Building Practitioner (LBP) with a carpentry or design licence. LBPs are legally accountable for restricted building work and can issue a Record of Work — important for your LIM and future property sales. Find a qualified local deck builder on tradedirectory.co.nz.
Also note: deck projects sometimes involve electrical work (outdoor lighting, power points) or plumbing — these are restricted trades requiring a licensed electrician (EWRB) or licensed plumber (PGDB) respectively.
Licensed Building Practitioner (LBP)
