Door canopy: bracket calculator

Give the width, the projection and the rise at the wall, and the calculator gives the number of brackets, the cutting list, the mass of the frame and the covered area.

A worked example: 1400 × 900

A canopy over a single door: 1400 mm wide, 900 mm of projection, 400 mm of rise at the wall, 40×20×2 section and 8 mm polycarbonate.

Mass is worked out without the corner radii of the section, so it comes out two to three per cent below the standard tables. No allowance is added for saw kerf or cutting errors: when buying, add one commercial length.

A bracket is a right-angled triangle: the leg against the wall, the horizontal projection and the diagonal between them. A triangle holds its shape by itself, so the canopy needs neither bracing nor heavy section — all its strength is in the geometry and in the fixing to the wall.

The fixing decides everything

The frame itself is almost impossible to break. It always tears away at the wall, and there the wall material matters more than the section:

• Brick and concrete — anchors through a plate, at least four points per bracket, 100 mm or more from the edge of the masonry.
• Aerated concrete — an ordinary anchor pulls out with a lump of block. Chemical anchor only, or a through bolt with a backing plate inside.
• Insulated wall — the fixing goes into the structural leaf through the insulation, with a sleeve: otherwise tightening crushes the insulation and the joint works loose.

The same rule of arm, strut and anchored plate governs other wall brackets, for an air-conditioning unit or shelves; they are covered under brackets and fixings.

Welding settings

A 2 mm wall, small joints and all of them on show: here the weld stays outside and at eye level. The values are the same as on the welding square tube page; the calculator above shows the row for the wall thickness you chose.

Materials and weight, part by part

The 1400 × 900 example with a 400 mm rise breaks down like this:

• Three brackets, each of three pieces: a 400 mm wall upright, a 900 mm projection arm and a brace of about 985 mm.
• Three purlins of 1400 mm — one every 450 mm of projection.
• All in 40×20×2 tube: 11.05 m at 1.76 kg per metre, about 19 kg of frame.
• 8 mm polycarbonate — 1.26 m², about 2 kg. 0.5 mm profiled sheet over the same area would weigh about 6 kg, 0.7 mm about 8 kg.

A bracket weighs about 4 kg and the whole canopy with its cover about 21 kg. One person can hold it up while another marks the holes, and with one bracket fixed to the wall first, the rest can be done single-handed. The 18 joints and 2.2 m of weld use less than 0.1 kg of wire — the end of a spool will do. There are twelve pieces, and they all come out of two 6 m bars.

Tools you need

• A welder good for 90–110 A on MIG or 70–90 A with a 2.5 rod. On a 2 mm wall MIG is easier: with a stick electrode thin tube burns through more readily.
• An angle grinder with a cutting and a flap disc.
• A 1:1 template — the bracket drawn full size on a sheet of plywood or steel, with stops along the outline.
• Magnetic 90° squares, 2–4 clamps, tape, level.
• A hammer drill and anchors to suit the wall — which ones is covered above, in the section on fixing.

Setting out and tacking

The three brackets have to match to the millimetre: the purlins sit on them, and any difference shows as a wave in the cover. So the brackets are not marked out one by one but welded on a single template.

1. Draw a 400 × 900 mm right angle and its hypotenuse on the template. Weld or screw stops along the outside of the outline.
2. The brace is mitred: at 400 by 900 its ends run at about 24° and 66° to its axis. The easiest way is to take the angle off the template by laying the tube on it.
3. Drop the three pieces into the stops, tack each joint on two sides, check the right angle with a square and lift it out. The next bracket goes into the same stops.

On the wall: brackets 700 mm apart — one at each end, one in the middle. Set the tops of the uprights on one line with a level or laser, not by eye from the door head: walls and openings are seldom truly level.

Step-by-step order with settings

1. Cut to the list. 12 pieces, deburred, weld areas cleaned to bright metal.
2. Brackets on the template. Settings for a 2 mm wall: 0.8 mm wire, 90–110 A, 17–19 V, or a 2.5 mm rod at 70–90 A. The acute corner of the brace is the thinnest spot: strike the arc on the heavier side and only then move towards the point, or the tip of the mitre burns away.
3. Wall plates. A plate for anchors on each upright, welded all round the tube.
4. Purlins. Assemble the whole frame upside down on the bench: three brackets on edge, purlins on top. The diagonals of the 1400 × 900 rectangle — about 1664 mm — must match before the purlins are tacked.
5. Clean, prime, paint — before fixing and before the cover.
6. Fixing. Offer up the frame, mark the holes through the plates, drill, anchor.
7. Cover. Multiwall polycarbonate with the flutes running down the slope, on screws with thermal washers; the top edge is sealed with solid tape, the bottom edge with breather tape so condensation can drain.

A 2 mm wall forgives less than the 3 mm of a carport: short welds, and no dwelling with the arc at a corner. More on avoiding burn-through in welding thin metal.

How to keep the brackets true

A triangle holds its shape better than a frame, but welding a thin wall still pulls it: a weld on one side of the mitre closes the angle and the arm lifts or drops. What helps:

• Weld in the stops and leave the bracket in the template until it is cold.
• Faces in turn: one side of the joint, the opposite side, then the narrow faces.
• Purlins alternately: an outer purlin to the left bracket, the same purlin to the right, then the middle one.

Painting

A door canopy hangs at eye level and every weld is on show. Dress the welds with a flap disc, then degrease, apply anti-corrosion primer and two coats of enamel, with welds and sharp edges brushed first. Cap the open tube ends. Do all of it before fixing: on the wall you cannot reach the top of the purlins under the cover, and nobody wants paint drips on the step and the door.

How long it takes

The smallest project in the section: 18 joints and about 2.2 m of weld. Most of the time goes not on welding but on the template and the wall:

• Template and cutting — the template has paid for itself by the second bracket.
• Welding the frame — a short stage once the pieces are cut and the template is ready.
• Painting — with drying times as per the product sheet.
• Fixing and covering — a separate day if the wall is aerated block and needs chemical anchors, which need time to cure.

For a wide entrance or a porch that needs posts, a carport-style canopy is the better build, and ready designs are reviewed on the metal door canopies page.

What usually spoils the job

Beginner mistakes on a door canopy

• Each bracket marked out separately. Three triangles come out different and the purlins sit in a wave. One template for all.
• Anchors into aerated block or insulation. The frame does not break — it is pulled out of the wall, fixings and all.
• "Carport" settings. Current for a 3 mm wall on 40×20×2 tube burns through the brace mitre in the first centimetre.
• Polycarbonate with flutes across the slope, or with open ends: water and dirt sit in the channels and the sheet turns green.
• Painting after fixing. Unpainted patches stay under the cover, and that is where the rust starts.

Author: Dmitry Frolov, welder and metal fabricator Updated: 28 September 2026