How to build shade cloth pergola frame?

justdoit-1

Hi all,

I want to build a frame for a shade cloth pergola in my front courtyard. I have a unit with a small front and back garden/outdoor space. The front is fully paved, about 4x5m. We need shade in summer but I want to be able to remove it in winter to maximise winter sun.

What I'm thinking is to place 4 posts, on each corner, with a hook at the top and then attach a Bunnings pre-made shade sail to the hooks. Then I can remove the shade sail in winter or in high winds or heavy rain. I'll also build a wooden raised garden bed around the base of each post, which I can use both for climbing plants and as a step to reach the hook.

Because I want to be able to easily remove the shade sail, I don't think it can be tightly tensioned, so will likely have a centre sag. Therefore it needs to be placed quite high for head clearance. I think 2.5m.will be ok (I'm 1.7m tall).

Lastly, the shade cloth needs to be easy to put up and remove, or I just won't do it 😅. Which is why I really want to think the design through.

Q1: If the posts are 2.5m high above ground, how much do I need to sink below ground? (Posts will be concreted in)

Q2: What kind of post would be best? I think I'd prefer wood for aesthetics and also to let me climb plants up. But I'm not sure how thick it needs to be or if circular or square is better.

Q3: can I use some kind of turnbuckle to provide a bit of tension for when the shade cloth will be up for a while? Or is that just complicating things?

MitchellMc

Hi @justdoit-1,

As a general rule, around one-third of the total post length should be below ground. So if you're looking for 2.5m of post above ground, you'd typically want around 1.25m below ground, meaning a total post length of approximately 3.75m. The exact depth can vary depending on soil conditions, wind loading and local building requirements, but the one-third rule is a good starting point.

The posts will need to be structural, which rules out round landscaping logs as they aren't graded for structural use. You may also find it difficult to source structural H4-treated timber posts, as most structurally graded pine posts are H3-treated and intended for above-ground applications. Steel posts are another option worth considering if durability is a priority.

It is quite common to use turnbuckles on one or more corners of a shade sail to allow it to be tensioned properly. I'd recommend incorporating them into the design. If the sail is left too loose, it can flap around in the wind, which places additional stress on the fixings and could eventually lead to damage or the sail coming loose. Turnbuckles allow you to get the sail reasonably taut while still being able to easily remove it when required.

One thing to keep in mind is that shade sails generally perform best when they are installed under tension and with some fall or twist designed into them. If you're planning on frequently removing the sail, you may want to look at the pre-made shade sail fixing kits available, as they can make installation and removal much quicker and easier.

Here's a guide on How to install a shade sail.

It's also worth noting that shade sails can be subjected to significant wind loads, even in relatively sheltered areas. If the posts, footings or fixings are undersized, there is a risk of structural failure which could result in property damage or injury. Before proceeding, I'd recommend checking any local council or building requirements that may apply in your area. If you're unsure about the post sizing, footing depths or overall design, it would be worthwhile consulting a suitably qualified builder, engineer or shade sail installer to ensure the structure is safe and fit for purpose.

Please let me know if you have any questions.

Mitchell