Hanging a heavy driveway gate on timber posts is well within reach for a capable DIYer, provided you use the right hardware and give your posts a solid foundation. Get the post sizing, hinge selection, and setting-out right from the start, and you'll end up with a gate that swings smoothly for years to come.
Assess the Gate Weight and Size First
Before you buy a single bolt, know your gate's weight and width. A typical farm-style or ornamental steel driveway gate can weigh anywhere from 40 kg to well over 150 kg. This determines everything — post diameter, hinge rating, and how deep your posts need to go.
- Measure the gate's width and height.
- Weigh it if possible, or check the manufacturer's spec sheet.
- Note whether it's a single swing or double swing gate.
- Consider the wind load in your area — exposed coastal or rural NZ sites put far more stress on a gate than a sheltered suburban driveway.
Choosing and Sizing Your Timber Posts
For a heavy gate, undersized posts are the number-one cause of failure. As a general guide:
| Gate weight | Minimum post size (H4 treated timber) | Minimum in-ground depth |
|---|---|---|
| Up to 60 kg | 150 × 150 mm | 900 mm |
| 60–120 kg | 175 × 175 mm or 200 × 200 mm | 1,000–1,200 mm |
| Over 120 kg | 200 × 200 mm or larger | 1,200 mm+ |
Always use H4 or H5 treated timber for in-ground posts in NZ — H3 is not suitable for ground contact. Check the treatment level stamp on the timber. PlaceMakers and Mitre 10 both stock suitable treated post timber.
The hinge post (the post the gate hangs from) takes the most load and should be the larger of the two if you're using different sizes.
Setting the Posts
- Dig your holes using a post-hole borer or manual bar and spade. Aim for a hole diameter roughly 3× the post width.
- Add a gravel base (100–150 mm of compacted AP20 or similar) at the bottom of each hole for drainage — this extends post life significantly.
- Set the hinge post plumb using a spirit level on two faces. Brace it temporarily with timber stakes.
- Set the latch post at the correct distance — allow for the gate width plus a small clearance gap (typically 10–20 mm each side).
- Concrete in both posts using a standard bagged concrete mix (e.g., 20 MPa). Fill around the post, tamp out air pockets, and slope the top of the concrete slightly away from the post to shed water.
- Allow concrete to cure for a minimum of 48–72 hours before hanging the gate. Ideally wait a full week before putting the gate under load.
Selecting the Right Hinges
For a heavy gate, heavy-duty weld-on or bolt-on strap hinges or hook-and-band hinges are the standard choice. Key points:
- Check the hinge's rated load capacity — use hinges rated well above your gate's actual weight.
- Use a minimum of three hinges for gates over 100 kg or taller than 1.8 m.
- Galvanised or stainless steel hardware is essential in NZ's coastal and high-humidity environments to prevent rust.
- Bolt-on hinges should be fixed with coach bolts (carriage bolts) that pass completely through the post, with a washer and nut on the back face. Never rely on screws alone for a heavy gate.
Bunnings stocks a range of heavy-duty gate hinges and hardware suitable for most residential driveway gates.
Hanging the Gate — Step by Step
- Mark hinge positions on the post. The top hinge should be near the top rail of the gate; the bottom hinge near the bottom rail. If using three hinges, space the middle one evenly between them.
- Pre-drill bolt holes through the post to avoid splitting.
- Attach hinges to the gate first (on a flat surface), then offer the gate up to the post with a helper or a temporary prop (a stack of timber offcuts works well).
- Check the gate is level and at the correct height off the ground — allow clearance for the driveway surface, including any gravel or paving.
- Mark and drill the post holes, then bolt the hinges through the post.
- Test the swing — the gate should open and close freely without binding or dropping at the latch end.
- Fit the latch to the latch post. A heavy-duty ring latch, slide bolt, or drop bolt is appropriate depending on your security needs.
Adjusting for Sag
Even well-hung gates can sag over time. Fit an anti-sag kit (a diagonal wire or rod tensioner) across the gate frame if it's a timber or light steel gate. For heavier ornamental steel gates, the frame itself usually provides enough rigidity.
Do You Need a Building Consent?
In most cases, a standard residential driveway gate does not require a building consent under Schedule 1 of the Building Act — but this depends on the gate's size, whether it's automated, and your local council's rules. Always confirm with your local council before starting work. You can find general guidance at MBIE Building Performance.
When to Call a Professional
Consider hiring a qualified fencer or tradesperson if:
- Your gate weighs over 150 kg or spans more than 4 m.
- You're installing an automated gate opener — electrical connections must be carried out by a registered electrician under the Electrical Workers Registration Board rules. Automated gate wiring is restricted electrical work.
- Your ground conditions are poor (soft fill, high water table, or rock).
- The gate is on a retaining wall or near a boundary where structural implications apply.
You can find experienced local fencers on tradedirectory.co.nz who can advise on or complete the full installation.
