A guide to everything you need to know to install a sun shade / shade sail post. From selecting the correct post dimensions, location and fixings, to what size hole and how to secure the post. Including tips to get the best results!
Before installing the post it is necessary to ensure it is in the correct place! Locating the post too close to the other fixing points will mean that you can never tension your sail correctly drastically reducing its effectiveness and longevity. Check out Planning for a Sun Shade and How to Install and Tension a Sun Shade for further information. Additionally, don’t forget to check with local authorities for any relevant building codes or permits that might be required for your shade sail.
Post Type and Dimensions
The type of post you choose (wood or steel) is usually dependent on availability and price. Wooden posts tend to be cheaper but sourcing suitably treated timber can be difficult in some areas. In either case it is possible to use round or square to meet your aesthetic requirements and it is worth adding that they can be painted, allowing them to match the shade color or indeed any other color scheme.
For DIY residential installations, in most cases the size of any one individual sun shade to be installed is unlikely to be bigger than 20ft x 20ft (6m x 6m). Even so, the size of the post required is still substantial, the loads on the post when the shade is correctly tensioned and allowing for wind cane be much higher than expected; What Load for the Fixings. As shown in the table below, the dimension needs to account for the height above the ground of the fixing point and the required depth of footing for that height.
NOTE: If you’re in the US, remember to always call ‘811’ before any project involving digging. Its a completely FREE service and they can help you pinpoint the areas you should not dig in.
As a general rule the depth below ground is about 1/3 – 1/2 of what is seen above ground.
This table is only meant to give you an indication of the post sizes used for differing sizes of sun shade, for posts with the shade fixing at a height of 2.4m or 3m above the ground. Do remember that you may not want all your posts to be the same height above the ground to allow for rain run-off or for aesthetic reasons.
The post length examples below are minimum as you will need to allow some extra post length for the actual fixing to be attached. ie you may need to allow an extra 3-4″ / 10-15cm for mounting the eye bolt.
Post To Buy (Minimum !)
(Square, Side Length x thickness)
|48sq ft 4.5m2||10’8″|
|5″ 125mm||75mm x 3mm||76.1mm x 2.3mm||2’8″|
|5″ 125mm||75mm x 3mm||76.1mm x 2.3mm|| 3′|
|96sq ft 9m2||11′|
|75mm x 3mm||76 x 3.6mm||3′|
|100mm x 3mm||88.9 x 3.2mm||3′ 3″|
|172sq ft 16m2||11′ 3″|
|75mm x 4mm||102 x 3.2mm||3′ 3″|
|100mm x 4mm||102 x 3.2mm||3′ 7″|
|269sq ft 25m2||12′ 3″|
|100mm x 4mm||102 x 3.2mm||4′ 3″|
|100mm x 5mm||114.3 x 3.6mm||4′ 3″|
|388sq ft 36m2|| 12′ 3″|
|100mm x 5mm||114.3 x 3.6mm|| 4′ 3″|
| 17 3/4″|
|8 7/8″ 225mm||5”Schedule 40 125mm x 5mm||139.7 x 4.5mm|| 4′ 7″|
**In the USA as a minimum it is recommended to use 4″ Schedule 40 Galvanised pipe.
Please note this is only an indicative guide and is not certified by a structural engineer. The information contained is not suitable to use for a building permit. All sizes are based on firm ground conditions and med/high wind areas. Sites and situations vary therefore these sizes will not apply to every situation. Please use this with care.
Using Smaller Poles; Using Stays / Guys to hold posts
If you need to use a smaller size of post or footing than the suggested dimension then it is possible to reinforce the posts with the addition of Stays / Guys. The ideal angle for the guy from the top of the post is 450 degrees but anything larger than 300 degrees should be OK as long as you are using suitable fixings. This technique is also frequently used if you are attaching multiple sails to a single post. These situations may require a structural engineer to ensure your post strength is suitable.
To ensure the long life of your shade structure it is necessary that the post will not degrade where it is in contact with the ground or indeed the concrete. Softwood should be treated to H5 level which will then allow the timber to be used in outside, in-ground applications where the timber will be subject to extreme wetting by fresh water. It also protects the post against termites, borers and very severe decay. This level of wood treatment is often used for retaining walls, piling, house stumps and building poles.
If using Hardwood post then the type of wood chosen should have durability of Class 1. The durability rating of a species (displayed as a Class) of timber relates to the natural ability of the heartwood of that species to resist decay and insect pests and Class 1 should last for 25+ years if it is in the ground.
Just as with wooden posts, it is necessary to ensure that the metal post will not degrade corrode (rust) too quickly and it should also be treated. A standard method would be buying Galvanised posts and then if desired it can also be painted or powder-coated (painting treatment).
It is also possible to buy Stainless Steel posts, which avoid some of the corrosion issues but they are substantially more expensive and it may be better to have such a post attached to a special mounting plate, that is set into the top of a concrete footing, rather than paying for and burying some of its length in the concrete.
Tip: If you shorten a metal post as part of your installation ideally you should also treat the ‘bare’ metal end that becomes exposed when it is cut. You can buy Galvanising spray or an anti-corrosion paint.
‘Hold Down’ bolts
‘Hold Down’ Bolts. I found in my research that some people suggested screwing in lag bolts (wood) or having a ‘hold down’ bolt (metal) screwed into the bottom of the posts where they are to be covered in concrete. These are to help keep the posts in place and stops them from possibly being pulled out of the concrete. I also found many people that said it wasn’t necessary. My feeling is that as it was easy enough for me to do, I added them.
Even a small movement of your footing will equate to the top end of the post moving quite a long way and will affect your ability to tension the sail, thus reducing the longevity of the sun shade. If you are digging through land fill or raised garden beds, these depths should not be included in the overall depth of the footing.
Tip: If your post location is currently covered in grass, then before you start digging like crazy, spend a little extra time cutting the turf and then taking a 2 inch slice off the top to give you usable turf to cover over the concrete footing after your post is installed .
As the table above shows the dimensions of the hole required for installing the post vary a little in diameter but more as regards the depth. Due to the depths required, before starting to dig, it is crucial to check where any services may be (gas, water, electricity, drains etc) to avoid adding to the work being done!
Once you have dug the hole to the required dimensions you need to add about a 4 inch (100mm) layer of medium size (~ 3/4inch / 20mm) gravel (~10Kg) to the bottom of the hole. This should then be compacted down to make it solid but it will still help with drainage and ensure the bottom of the post is not surrounded in water.
If once you have dug the hole to the required dimensions you find that the sides and / or the base of the hole are not holding their shape then it is suggested to go a little deeper and then add a layer (4″ /100mm) of concrete to the bottom of the hole (and allow it to set) or a reinforced concrete paving slab before adding and compacting the gravel.
Concreting post for Sun Shade
When positioning the posts ready for concreting, they are ideally leaning at an angle of about 5 degrees away from the center of the shade. This is not absolutely necessary but recommended as it does counteract bending of the post when the shade is tensioned. If using square posts then also ensure that one of the flat faces is facing the center of the shade in preparation for the fixings. With the post in the correct position you will then need to set-up some bracing to hold the post in position while the concrete is setting. Even with bracing, when first adding the concrete to the hole it is easy for the bottom of the post to move, so carefully adding the first few inches of concrete and checking your post position is recommended.
How to measure a 5 degree lean on the post.
If the angle of the post is not exactly 5 degrees from the vertical, it is not a problem. Some suggest 10 degrees and other sites (mainly for smaller shades) do not even mention having the pole at an angle.
Make a temporary mark (A) on the post; anywhere along its length but usually just above where ground level will be works well. Then measure up the post 40″ (~100cm) and make another mark (B). From the bottom corner of a spirit level measure up the spirit level 40″ (~100cm) and make a mark (C).
Hold the bottom corner of the spirit level at point A against the post. Keeping the spirit level vertical lean the post away from the center of the shade until the distance between points B and C is 3 1/2″ (9cm).
Increasing the distance between B and C increases the angle; for ~10degree lean make the distance 7″ / 18cm.
Concrete Mix and Pour
The posts should be embedded in concrete with at least a 20Mpa rating. This is a strength rating for the concrete and is determined by the ratio of cement to aggregates, sand and water. (Approx 1:3:3 + water) Ready mix concrete bags will have the information on them and different cement manufacturers have different suggestions. Follow the manufacturers instructions as incorrect ratios and adding additional water can reduce the strength. Conditions vary for different environments, if unsure of the concrete type best suited to your area contact your local concrete supplier.
Sun shade post ready for concrete; with hold-down bolts, protective plastic and tape for measuring the angle of lean.
Top Tip: If you tape some plastic around the post just above where ground level will be then any concrete splashes when pouring your footing will not stain your post.
When filling the hole you should slope the top level of the concrete slightly away from the post to assist with water draining away. If your post is in a grassy area then stopping the concrete an inch or so below the top of the turf allows you to then replace the turf you cut earlier. Depending on the manufacturer you should then leave the concrete for 48 to 72 hours to set before applying any load to it.
The finished Post set-up.
Check out How to Install and Tension a Sun Shade for attaching your fixings and the final setting up of your shade!