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.
| Item | Section | Length, mm | Qty |
|---|---|---|---|
| Bracket, wall leg | 40x20x2 | 400 | 3 |
| Bracket, projection | 40x20x2 | 900 | 3 |
| Bracket, diagonal | 40x20x2 | 985 | 3 |
| Purlin | 40x20x2 | 1400 | 3 |
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.
A door canopy is the one place where snow off the roof lands directly on it. With a roof slope above the door, the load can be two or three times the flat figure. The answer is pitch and a snow guard on the main roof, not a heavier section.
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.
| Wall, mm | Section | MIG/MAG | MMA |
|---|---|---|---|
| 1.2 | 20×20, 20×40 | 0.8 mm · 50–70 A · 16–17 V | 2.0 mm · 50–65 A, stitch welding |
| 1.5 | 40×20, 40×40 | 0.8 mm · 70–90 A · 17–18 V | 2.0 mm · 55–70 A, stitch welding |
| 2.0 | 40×40, 60×40 | 0.8 mm · 90–110 A · 17–19 V | 2.5 mm · 70–90 A |
| 3.0 | 60×40, 80×40 | 0.8–1.0 mm · 120–140 A · 19–21 V | 3.2 mm · 90–120 A |
| 4.0 | 80×40, 100×50 | 1.0 mm · 140–170 A · 19–21 V | 3.2 mm · 110–140 A |
What usually spoils the job
| What went wrong | Cause | How to avoid it |
|---|---|---|
| The frame twisted | Welds run one after another on the same side | Alternate corners, weld in short runs |
| The diagonals came out unequal | Nobody checked them before tacking | Measure both diagonals twice |
| Burnt through the wall | Too much current for 1.2–1.5 mm | Turn it down, stitch it with pauses |
| The corner welded on one side only | Saving time | Weld both sides wherever the joint takes load from two directions |
| Rust from the inside within a year | Open ends | Caps, or weld them shut |
Frequently asked questions
How far should a door canopy project?
Not less than the depth of the open door plus the space where a person stands: for a 900 mm door, 900–1200 mm. Less than that and rain still reaches the threshold. Beyond 1.5 m it needs braces at a different angle and a snow calculation.
How is it fixed to the wall?
To brick and concrete, anchors through a plate, at least four points per bracket. To aerated concrete, chemical anchor only or a through bolt with a backing plate inside. On an insulated facade, into the structural leaf with a sleeve.
Polycarbonate or profiled sheet?
Polycarbonate is lighter and lets light through — 1.5 kg/m² against 4.5 — and over an entrance that shows in the anchors. In exchange it drums in the rain and hazes over in 7–10 years. Sheet is quieter and lasts longer but darkens the doorway.
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