Designing a Simple Driveway Gate in Metal

Start With the Opening, Not the Gate

Before you order a single length of steel, spend twenty minutes with a tape measure and a notebook. Measure the gap between the piers or posts at the top, the middle and the bottom, and work to the narrowest figure — old brickwork is rarely square, and a gate built to the widest measurement will jam the first time it rains. For a single gate, a clear opening of 900mm to 1200mm is comfortable; beyond about 1500mm, consider a pair of gates instead. Take the site levels too, because a sloping driveway changes everything. As a rule of thumb, allow 10mm of clearance at each side and 150mm between the bottom rail and the ground if the ground is flat. On a slope, that gap needs to follow the fall, not the gate.

Sketch the gate full size on the bench or floor — a chalk rod drawing saves more time than any amount of arithmetic.

Deciding on the Frame Sections

A driveway gate is a lever, and every kilogram at the far edge loads the hinge stile. Keep the outer frame to 40 x 40 x 3mm box section for gates up to about 1.2m wide, stepping up to 50 x 50 x 3mm on anything larger. Infill bars in 20 x 20 x 2mm or 16mm round bar look well and add stiffness without much weight. If you want a timber or composite infill panel, plan for 30 x 30mm rails and remember that a solid panel turns the gate into a sail — it will need heavier framing and a stiffer post.

• Hinge stile — the vertical at the post side; make this the heavier member if the sections differ.
• Slam stile — the free edge, carrying the latch.
• Top and bottom rails — cut them to the inside of the opening so the frame closes on square corners.
• Infill — vertical bars at 100–120mm centres, which is both a good visual rhythm and a sensible safety spacing.

Bracing — the Diagonal That Does the Work

Without a diagonal, a welded rectangular frame will drop at the latch corner within a season or two. The brace must run from the bottom of the hinge stile up to the top of the slam stile, so that the weight of the gate puts it into compression. Get that direction wrong and the weld at the corner is carrying the load in tension, which is exactly where a weld fails first.

Use flat bar, 40 x 6mm or 50 x 6mm, set flush with the frame face. A single diagonal is fine on a gate up to 1.2m wide; a pair forming a shallow V, or a diagonal in each half of a double gate, is better on anything wider or taller than 1.5m. Fit the brace so it can be welded along its full length rather than butted end-on — a longer seam spreads the load and resists flexing.

Hinges and Posts: Where Gates Usually Fail

Most sagging gates are not a gate problem, they are a post problem. A 100mm square, 3mm wall box post set 600mm into concrete is the sensible minimum for a gate up to 1.5m wide; a 4mm wall or a 100 x 100mm angle frame is better still. Remember that gates pull on the post in a direction the post was never designed for, so pack the hole well and let the concrete cure for a full week before hanging anything.

For the hinges themselves, you have three practical choices:

• Weld-on adjustable hinges — strongest and neatest, with a threaded barrel or slotted plate that lets you correct drop later.
• Bolt-on adjustable hinges — kinder if you may need to replace them, but the bolts must go through the stile, not into it.
• Hook-and-band hinges — traditional and forgiving, but they need a heavy post and a good drop bolt to stay true.

Set the top hinge as high as the gate allows and the bottom hinge roughly a quarter of the gate height up from the bottom. That spread of two points is what resists the twisting force of the swing.

Latch, Stop and Ground Clearance

A latch alone will not hold a gate steady — it needs a stop to close against. Weld a small plate or bracket on the slam post so the gate lands on it rather than rattling in the wind. A drop bolt on the slam stile is worth the small extra cost on any gate over a metre wide, and it takes the strain off the latch and the post in one move. Check the swing arc with a piece of chalk on the ground: the bottom corner must clear any slope, kerb or gravel ridge across the full travel.

Finishing Before You Weld It Shut

Preparation is most of the finish. Degrease the steel, wire-brush away mill scale and rust, and drill small drainage holes at the lowest point of every closed section so water cannot sit inside the box and rot it from within.

Hot-dip galvanising gives the longest service life, but it must be done before any paint and it will distort thin panels, so plan it into the design. If you are painting, use a zinc-rich primer followed by two coats of a good metal topcoat, and paint the gate before you hang it. Touch in every weld and every scratch afterwards with the same system — bare steel left exposed is where the rust always begins.