Shade Sails

‘Shade sail’ From Wikipedia

A shade sail is a device to create outdoor shade based on the basic technology as a ship’s sail. Shade sails use a flexible membrane tensioned between several anchor points referred to by us as tensile structures. While generally installed permanently, they are cheap and easy to set up. They are usually provided above public gathering places such as seating areas and playgrounds in countries where strong sun radiation makes prolonged stays in the open sun unpleasant or dangerous due to sunburn and skin cancer risk.

History

Ancient Egyptians and later the Greeks and Romans used large pieces of fabric to provide shade. The Colosseum in Rome was shaded with large canvas “sails” pulled into place by Roman sailors. Modern Shade sails came into wider use with the invention of a far more durable and relatively inexpensive fabric called shade cloth. Useful versions of shade cloth appeared in the early 1990s especially in Australia and South Africa.

For most of the 1990s, there was some confusion about what these new devices should be called however they are now most commonly called shade sails throughout Australia, South Africa and the U.S.A. Shade sails have yet to have a significant impact in Europe and South America

A number of Australian shade sail businesses export to other countries. Rapid growth in the “shade sail industry” has seen many new businesses and websites offering shade sails and shade structures.

Current technology

Originally shade fabric, like all fabrics in the outdoors, suffered from UV degradation. UV inhibitors are now added during the manufacture of shade cloth and good shade cloth now generally comes with a multi-year UV degradation warranties. Shade cloth is a knitted fabric and this is an important factor in using it to design and manufacture shade sails.

Successful shade sail design uses the inherent “stretch” of the knitted fabric to create three dimensional shapes. Fabrics other than shade cloth are used to make shade sails such as PVC, a more expensive alternative, or canvas variations. The low cost of shade cloth and its ability to breathe makes it a prime choice for “cool shade”.

Installation

Modern purpose-made shade sails vary in shape, size and colour and there is a trend towards installing multiple sails, sometimes overlapping, thereby adding some form and style to its function. Shade sails are tensioned usually by means of either a stainless steel turnbuckle or a pulley system fixed at each corner of the sail.
For permanently fixed sails, the turnbuckle provides the best means of fixing the canopy since it generally allows more tension to be applied. For sails that are used on occasional bases, the pulley system is more practical since it can be set up and taken down in a couple of minutes.

For domestic applications of shade sails it is recommended to install them with a quick release “snap hook” at each corner. This allows the shade sail to be quickly taken down in high wind conditions or during the winter season. Correct installation requires that adequate and quite considerable tension be applied to the sail to allow it to adopt its correct shape and prevent flapping in the wind. It is important to ensure that the mounting points are substantial and secure both to be able to accept the required initial tension and to absorb the loads created by wind gusts hitting the sail – (Wikipedia).

Covering areas of the great British outdoors is a growing trend, from nursery schools to nature reserves, cafes to car parks the requirements run on. The importance of learning outside the classroom and access to all-year-round outdoor play has also lead to an increase in the canopy market. Often these needs are met and arguably sometimes better served with steel and polycarbonate type structures (see Motiva Pages) however fabric has a large part to play in canopy design and construction often offering more flexible design and great looking fabrics structures at often less money.

In addition, we are more knowledgeable than ever before about skin cancer and its causes, children are most at risk from the sun’s harmful UV rays therefore shade provision for children is vital. There are around 10,500 cases of melanoma diagnosed each year; the number of cases had almost tripled since the early 1980s. Over 2,300 people die from skin cancer each year in the UK. In fact, there are more skin cancer deaths in the UK than Australia, even though Australia has more cases of the disease. A single case of sunburn for a young person can have dire consequence later on in life. Proving areas of shade is essential for all schools.

Before installation it is very important that we consider the most suitable location for your Shade Sails taking into account many factors:

1. The direction of the sun, as you want to provide the maximum shade for your area.
2. The location and heights of your fixing points.
3. It’s important to ensure there are differing heights for your fixing points, as you do not want the Shade Sail to lay flat. By ensuring you have a ‘twist’ in your shade sail, not only will it be more aesthetically pleasing to the eye, but it can be tightened up more effectively, and will reduce sagging in the middle of the Shade Sail.
4. It’s best to have four fixing points, two low and two high, diagonally opposite each other. Keeping in mind where the sun is, you will want a low fixing point to block out the sun. The higher the fixing point, the more likely the sun is going to shine underneath the Shade Sail.
5. When choosing Shade Sail positions and layouts, be aware of any underground services in the vicinity, as we will need to be advised of these.
6. Does the Shade Sail need to add year round value by being waterproof?

A good Shade Sail design means efficient manufacture, straightforward installation and ultimately, good value. We are always focused on the design of your Shade Sail, making sure it has the right shape, is supported appropriately, and is therefore the best solution overall. When properly tensioned, a Shade Sail will not wrinkle, sag or flap in the wind. Shade Sails that are not properly tensioned end up holding water, hanging limp and becoming unstable in heavy winds. Shade Sails work best when they are under enough tension to give curvature, are not a level plane and are ‘twisted’ for stability.

If you are not choosing one of our standard Shade Sail designs, we will ask you at the early stages of the enquiry about the shape that you would like the Shade Sail to take. We do this to make sure we fully understand your expectations before we can begin to outline a form that works perfectly for you and the application. From sketch drawings, design development then continues, working out specific forms, interactions of the steel and fabric, water run-off etc. This culminates in a complete design proposal that is ready for sign-off.

In a ‘stand alone’ contract i.e. where the Shade Sail is the main or only item/works package we will take responsibility for the whole project including foundation design, construction and reinstatement.

Where the shade sail is part of a larger scheme the client would often have their own “design and build” team of architect, structural engineer and main contractor. In these cases, we would supply to the client loadings that our Shade Sail would impose on the clients building/grounds. The client’s engineer would then assess these loads and design a suitable foundation/supporting structure, according to the local ground conditions/underground services. The main contractor usually excavates for and provides the shade sail foundation as designed by the client’s engineer.

Shade Sail footings range in size according to the height of the posts. In general, one third of the total length of post will be embedded in concrete in the ground, with the remaining two thirds above the ground. Widths of footings are generally 600mm – 1200mm, this increase according to the Shade Sail size and diameter of posts.
When concreting in the steel posts we often lean the posts back slightly on approximately a 5 degree angle. This helps with aesthetics as when your Shade Sail is tightened up, the posts may bend inwards slightly.

We recommend the use of steel posts ranging in size from 140mm diameter up to 500mm diameter dependent on the size of the Shade Sail. The taller (higher) the post and the bigger the Shade Sail, then the larger the posts will need to be. (This will be the same for the Shade Sail footings).
For the posts, we recommend galvanised steel. Galvanised steel will avoid rust and is a better solution for fixing Shade Sails to than wood. Wooden posts can warp which place the sail out of alignment and can rot over time and lose their strength. (Galvanising is where the steel is submerged in molten zinc and when the zinc reacts with the steel a protective coating is formed). This coating improves the steels anti-corrosion performance to ensure it lasts as long as possible with little to no maintenance. Galvanised finishes are extremely durable in their own right, and on a thin sheet, the visual appearance is quite striking and attractive. However, on thicker, structural section, the finished in not always as consistent, so in many cases, a topcoat is advisable applied in the form of a polyester powder coating or a wet paint system. Some structural sections are too large for hot dip galvanising so a wet paint primer system would be used.

If attaching Shade Sails to existing structures, you must ensure that the structure is adequate to handle the loads applied to the Shade Sail fixings during instances of poor weather and high winds. If unsure, we can advise on this. We engineer our posts and footings to ensure structural integrity, longevity and superior performance. They are also installed at the depth required to ensure your Shade Sail will be safe and structurally sound for years to come.

There are a range of different caps available for the top of our Shade Sail posts’ however we always recommended welded caps for longevity and improved aesthetics.

Included in our service is the development, in 3D of the fabric form, with industry-specific fabric form development software, using fabric panel shapes to create the appropriate form. This is developed in conjunction with our engineers in order to avoid excessive load, be it wind, snow or physical weight.

The two most popular fabrics used in external canopy structures are high density polyethylene shade cloth and PVC coated polyester PTFE coated glassfibre is another option for larger structures.

High density polyethylene shade cloth is manufactured specifically for shade sails. The long direct sunlight life of fabric is guaranteed by treatment with UV stabilisers. The average shade rating of Shade Sail fabric is about 90%. The UVR block is close to 95%. That’s what makes our Shade Sails an excellent protection from skin cancer. The stitching is done with locking stitch and “Tenara” thread is used throughout.

PVC (poly vinyl chloride) coated polyester is the waterproof option. The PVC coating includes various agents and pigments to help prevent degradation of the “high strength-low stretch” polyester base cloth, and the top coating area of an especially high quality, to minimise dirt build-up, to facilitate leaning and to maintain the appearance of the fabric for many years. All but the most lightweight fabrics developed for canopy use would have a life expectancy of at least ten years.

PTFE (poly tetra flouro ethylene) coated glassfibre offered a truly long-life material. The RTPE coating is resistant to virtually all chemicals, and will not degrade in the harshest of climatic condition. The material has a life expectancy in excess of 20 years, although there are some structures in this fabric that have been in existence for even longer than this.

Many Shade Sails are made by joining flat fabric strips together and then marking the Shade Sail shape out on top of the large panel and then cutting it out. The result is a flat shape which when installed, is forced into 3D shape through shearing force. While this approach appears to work, it is often only short term, ultimately there are limitations and typically these Shade Sails will have a shorter life than properly patterned sail. These Shade Sails will often be flatter than desirable in order to overcome wrinkles in the body of the sail which result from lack of proper patterning. While you may be shown photos of apparently excellent Shade Sails as evidence to demonstrate qualifications and competency, bear in mind it is unlikely you will be shown photos of the large number that “didn’t quite work out” or photos of the “nice Shade Sails” a few years later when they have either sagged or flogged themselves to destruction.

Correct patterning results in 3D shape when the fabric panels are joined without the need for shearing force. The strips of fabric have curves cut in the sides which are defined by 3D patterning software and are usually cut on a computer-controlled plotter/cutter.

There are basically 2 types of Shadecloth fabric which are defined by their construction, mono/tape and mono/mono.

Mono/tape fabrics are constructed using mono filament yarns (similar to fishing line) with flat or elliptical shaped tape woven through them to help close up the gaps and thereby afford higher shade performance whilst keeping the fabric light.

Mono/monofabric has no tape so is typically heavier as it requires much denser weave in order to achieve required shade performance figures. These fabrics typically provide higher tensile strength than mono/tape fabrics and are much more stable – i.e. they have similar technical performance figures in both weave directions.
Shadecloth Weight – typically correlates directly with tensile performance – heavier fabric is generally stronger than lighter fabric and is, therefore, typically used for larger Shade Sails and light fabric for smaller Shade Sails. Fabric weight falls into broad groups, light 200-250gsm, medium 300 to 350gsm, heavy >350gsm.

Fabric weight also correlates directly with forces applied to structures which the sail is attached to. Heavier/larger Shade Sails require higher stresses to be applied to ensure the sail is sufficiently taught and therefore exert larger forces on posts resulting in larger steel sections and footings/foundations. Another example of marketing misinformation is the claimed shade performance number typically 90-98%. This number is determined by placing a small sample of fabric on a light source and measuring light transmission through the fabric. The test bears no relationship to how the fabric is used in Shade Sail application. When the shadecloth is stressed in both directions significant gaps appear in the weave changing the ability of the fabric to provide claimed shade performance numbers. The small difference in performance between the “90%” group of fabric is in our opinion insignificant given the fact they all stretch when deployed. The important thing is to ensure that the fabric is real commercial grade and in the 90% category (70% and 80% fabrics are unsuitable for use in human protection applications).

The majority of Shade Sails are too big to fit inside the width of fabric off the roll therefore, they are made by joining strips of shade cloth together to form larger panel – this process is called seaming.

Seams should be carefully located with aesthetics in mind – Shade Sails, after all, are not just functional and should include an architectural element. Let’s say your sail is 4m wide and the fabric width is 3.8m wide – where is the seam going to be located. All too often cheap sail will be made by joining thin 200mm strip of fabric to one side of the 3.8m to make the 4m – while functional and low cost – visually, it is very unattractive. Another common problem is the method used for seaming – the common methods used are shown below – professional high performance Shade Sails should be made using the Lap Seam with rows of lock stitching to provide full shear capacity.
The most commonly used low cost threads are a blend of polyester and cotton – these are UV stable, however, typical life expectancy in Shade Sail application is between 5 and 15 years depending on the amount of stress. Thread strength drops by up to 50% over this time due to exposure to UV – the higher the sail is stressed the quicker it will fail. High performance Shade Sails are made using PTFE thread which costs 10 times the price of a comparable poly-cotton blend. PTFE threads loose less than 20% of their strength with UV exposure over 10-15 year period.

The two commonly used edging methods for Shade Sails are webbing and cable. Both methods are suitable for making Shade Sails however load capacities vary. If webbing is used then it should be placed on the bottom side of the shade fabric to protect the web from UV radiation.

The edge of the shadecloth should be folded under the web so there is no raw fabric edge exposed which is visually unattractive and subject to unsightly fraying. The same applies if cable or rope edge pocket is used – the edge of the shadecloth should be folded under the hem forming the pocket and rows of stitching used. Often edge pockets are formed by simply folding and sewing the fabric leaving the raw edge of fabric exposed – while this is a low cost method it is extremely unattractive.

Most webbing used in the shade industry has a tensile capacity of approx. 18kN which is equivalent to approx. 6mm stainless wire. The size of the sail and its edge length will be limited by this capacity; hence larger Shade Sails (with edges of greater than 8-10m) are typically made using cable edges.

The most commonly used shade sail corner fitting is stainless steel “O” Ring. These are available in various quality standards and sizes. The fitting is created by forming a piece of solid rod to the required shape. The low end uses or 6mm thick 304 grade rod which are formed but often not welded closed – they have very low strength and will be prone to rust. These fittings are suitable primarily for small budget Shade sails and internal applications. High performance Shade Sails use a thick “O” Ring made from 316 grade stainless steel.

Rings are used to fasten the Shade Sail by either a shackle or turnbuckle to a point either on a post or an existing structure. Each corner of our Shade Sails has an extra layer of cloth and strapping which serve the purpose of distributing forces.
The perimeter of each Shade Sail features a curve that controls the tension of fabric in the centre of the sail. The fabric, therefore, has uniform tension throughout.

All our Shade Sail fittings are marine grade 316 stainless steel or chrome-plated brass, which not only look tasteful and modern but have also been tested for their strength and durability to ensure their longevity.

Beware and avoid the hook style turnbuckles which are often used by Shade Sail suppliers for their convenience during installation. Aside from the danger posed by one of these coming un-hooked in high winds. In our opinion, hook turnbuckles are completely unsuitable for use in Shade Sail applications. Beware of firms using any type of fixing that you could not adjust without specialist equipment if you chose to, this is a ploy to tie you into their maintenance service.

To clean your Shade Sail, we recommend the use of a mild detergent with the use of a low-pressure water hose and a soft scrubbing brush. Do not use abrasive cleaners or a stiff brush. Do not use chlorine-based cleaners.

Ensure that the Shade Sail does not come into contact with chemicals, as this will damage your Shade Sail, and this is not covered by the warranty.

You may wish to take your Shade Sail down in the winter months. It’s preferable to store the Shade Sail in a protective bag to keep out the vermin. We can offer this as a service.

Fabric is a great diffuser of light. The top surface of the canopy may become dirty over time, but from the underside, the surface soiling is rarely noticed. Although the translucency of the fabric will have reduced accordingly, it’s quite surprising how little this affects the comfortable levels of light under the membrane.

In most cases, Shade Sail cleaning is a very easy operation to carry out. The purpose is primarily to remove built-up areas of permanent dirt, on both the fabric and the steelwork which can act aggressively against the surface. A secondary benefit is improved brightness under the canopy.

It would be good practise to clean most structures every couple of years. However, on large structures, access to all areas of the canopy is unlikely to be easy, so cleaning may well be less frequent. In many cases, however, cleaning can be quickly and easily carried out by any cleaning contractor or caretaker using mild detergent, soft brushing and lots of clean water to rinse.

By ensuring long term cleanliness of the Shade Sail, the benefits will be a longer life for the fabric, and a better looking, better-maintained structure.

However, it’s important to stress that all of the Shade Sail fabrics are extremely strong and durable.

Most shade-cloth suppliers offer 10 year warranty which we recommend you consider of little or no value. The warranty is typically against “UV Degradation” only and is voided if the sail has been “over-stressed”. Both conditions are difficult to prove particularly since suppliers do not specify how much stress is “over-stressed” and installers don’t measure pre-stress. Mostly, warranties only cover the supply cost of the fabric on pro-rated basis, i.e. in 5 years if you can prove claim of UV Degradation, then they will pay 50% of the cost of the fabric (when it was purchased) provided your supplier is still in business and can produce receipt to prove the purchase. There is no contribution to the cost of removing, remaking and re-installing the shade – labour is the highest component cost of professionally manufactured and installed Shade Sail.

The most valuable warranty is the one offered by the Shade Sail supplier so it is important that you select a reputable supplier who understands firstly, how to design good Shade Sail and then how to make a quality sail. It is also important to deal with a company who will be in business long enough to provide support if required!