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How the calculator works
The most common mistake with a shade sail is buying one the same size as the space. A sail has to be smaller than the distance between its fixing points, because the hardware at each corner needs room and the sail has to be pulled tight.
- Gap at each corner: 1 foot for spans up to 15 feet, 1.5 feet for longer ones. So a 12 x 16 foot space takes a sail of about 9 x 13 feet.
- Standard size: the calculator picks the largest sail sold off the shelf that fits inside those limits.
- Slope: one corner goes lower than the rest, about 1 foot for every 5 feet of sail, so rain runs off. A flat sail collects water, sags and tears.
How to measure
Measure between the points where the hardware will attach: the eye bolt on the house wall, the hook on the post. Measure the real distances, not the size of the patio under them.
For a triangle, enter the shortest of the three distances. Standard triangles have three equal sides.
Rectangle or triangle
A rectangle shades about twice as much as a triangle between the same points. Triangles look lighter and need only three fixing points. Two triangles overlapped at different heights give more shade and look better than one.
Fixing points
- House wall: fix into the frame or masonry, never into siding or fascia boards alone.
- Posts: steel or 6 x 6 timber, set in concrete to a third of their height above ground and leaning slightly away from the sail.
- Hardware: a turnbuckle on at least two corners, so you can tighten the sail after it stretches.
Take the sail down before storms and for winter.
A sail is one of eleven ways to shade a patio. The others, with what each costs in space and effort, are in patio shade ideas.
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