Shade sail posts & footingsThe post is only the visible part.
Where a corner can land, what the ground has to resist, and what to do if an existing post has moved.
A sail pulls on its supports long before any wind arrives. The post, the connection, the footing and the ground all work as one thing, which is why no chart turns a sail size into a post size. Start with where people need shade and where they need to walk. The supports get designed around that, by someone who has stood on the ground in question.
What the footing does
Think of the post as a lever. A sideways pull high above the ground tries to turn the whole post and footing over. That is why a taller post or a bigger sail can need a very different hole underneath it, even when the steel above ground looks much the same. Soil, rock, fill, next-door foundations and the combined pull of two or three sails all feed into it.
Plenty of posts are raked away from the sail on purpose, so a lean on its own tells you very little. What matters is whether it has moved since the day it went in. That's what the handover photos are for.
Three ways to support the corners
What needs checking
New posts in the ground
The usual answer when the cover has to reach away from the house. Check what is buried first, and leave room for the footing itself, the machine that digs it and the path people will walk afterwards.
A connection to the house
The pull has to reach real structure by a route somebody has assessed. What you see from outside can be hiding a cavity, light framing, or a member that was never asked to do this.
Existing steel, timber or a slab
A pergola that feels solid under your hand was built to hold a roof up, and a sail pulls sideways on it all day. Have the condition, the connections and the foundation assessed for the sail you actually want.
Count your corners before you count your posts. Every corner has to land on something, so a four-corner sail needs four fixing points and a five-corner sail needs five. If only two of them can come off the house, you are buying the rest as posts. That is usually where a budget moves, and it's better to know at the sketch stage than at the quote.
The drawing shows why bolting to gutter, fascia or a single skin of brick is the shortcut that comes back. Even where the fixing does reach a rafter or a beam, somebody still has to check the member, the bolts, the bracing and how the hole gets weatherproofed.
Mark the things the post must miss
- People: door swings, the chair pulled out from the table, the route to the bins and any access path that has to stay clear.
- Below ground: pipes, cables, drainage, pool equipment and nearby foundations.
- Above ground: overhead services, roof edges, windows that open outwards and the tree that will be twice the size in ten years.
Before You Dig Australia says its plans are indicative and can miss private services altogether. The contractor still needs a proper locating process before anything goes in the ground. Dig out whatever records you have for pool pipes, garden power or that bit of building work from years ago.
What to expect before the sail goes on
Get the support layout and the footing requirements settled before the membrane is ordered. Ground conditions sometimes need a closer look, and an existing structure may need records or an inspection before anyone hangs a sail off it. We are a licensed builder, 294924C, and the support drawings come with certification on request if a council or an insurer asks for it.
Steel or timber?
Both do the job. Compare the look, the finish, how each one ages and what upkeep you are signing up for. On timber it is the condition at the connections that matters; on steel it is the coating at ground line. Neither material gives you much warning before it lets go, which is why a walk around once a year earns its keep.
Ask for a drawing that names the supports, says what their design is based on, and lists what you are handed at the end. The standards guide explains how the fabric and the structure get assessed separately.
Can shade sail posts be bolted to an existing slab?+
Sometimes. It depends on how thick the slab is, whether it was reinforced for the job and how far in from the edge the base plate lands. A garden-variety patio slab was poured to be walked on, and a post levers up on one corner of it all day. More often the post ends up beside the slab with its own footing.
My post is leaning. Can it be straightened?+
Sometimes. If the footing has turned in the ground but the concrete itself is sound, the post can come out, get re-stood and re-poured. If the concrete has broken up, or the steel has gone at ground line, it gets replaced. Either way the tension comes off the sail first, which is the bit people try to skip.
How long between the posts going in and the sail going up?+
Long enough for the footings to cure, which is why the posts go in on one visit and the sail goes up on another. Concrete keeps gaining strength for weeks, but the first few days do most of the work. Your installer should give you the date for the second visit while they are still standing in your yard.
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