Tensioning Shade Systems
Properly tensioning a shading system can be complicated, but it doesn’t need to be impossible. Getting it right is critical to the stability and durability of the structure. Too little tension, and the structure risks damage from wind or pooling water. Too much, and the attachment points may break, supporting structures may bend, and the fibers of the rope or shade cloth can degrade, creep, or create injury risks in the event of a failure. The following four considerations will help ensure a safe, effective, and long-lasting shade structure.
1. Every Attachment Point Needs TensionAny loose attachments will lead to billowing and sagging in the fabric of the shading system in at least one dimension, which is typically problematic. While some might expect loose attachments to put less stress on the ropes and fabric of the structure, the reality is that it can allow the fabric to bubble and catch wind like a parachute. This creates a risk of sudden shock loads on your sail shade hardware when strong gusts slam into the cloth. Such forces may exceed the intended load of the system’s hardware, ropes, or fabric, causing it to snap, pull loose, or rip.
Shade sail sagging from low tension is also undesirable in calm conditions because rainwater on an outdoor shading system can collect and put far more weight on the fabric structure than it can safely support.
2. Some Stretch is Desirable — But Creep Is NotThe inherent stretch of knitted fabric helps shading systems create smooth, consistent surfaces without baggy or wrinkled areas. A small amount of stretch in ropes fastened to the fabric’s corners can serve a similar purpose. Without any stretch in the soft goods, the system would be stable but difficult to balance the tension on all attachment points or create helpful curvatures or 3D shapes in the shade (discussed in #3, below). Too much stretch in the fabric can cause similar issues as too little tension: wind and water could pick up the slack in the stretchy fabric or rope causing it to sag or billow.
Another factor to consider is rope creep, defined as an unrecoverable stretch of the rope. High tension in shading systems exerts a constant pulling force on the soft goods. Over time, this force can cause permanent stretch that will gradually loosen the ropes and fabrics, requiring re-tensioning or replacement. The most successful designs will use ropes that have a minimal tendency to creep under tension, such as Robline’s Ocean 5000.
3. CREATING ADVANTAGEOUS SHAPES: HYPARHypar, which is short for hyperbolic paraboloid, refers to a saddle-shaped surface which is desirable in shading systems. The twist or 3D shape of a hypar can be created by alternating high and low corners on the shade, and the benefits include increased tension, reduced flapping, and preventing water from pooling on the shade.
(Source: Formfinder - Typology)
Triangle shades always remain flat as it is not possible to create a hyperbolic paraboloid shape with only three corners. This means triangular shade structures are more prone to flapping and holding water than hypar structures. At least four tensioned attachment points are best for the longevity of shading systems.
4. Select the Appropriate Attachment HardwareSome typical shade structure connection points include stainless steel turnbuckles, pulley systems, or “quick release” snap hooks affixed to the corners of the fabric.
- Turnbuckles are ideal for tensioning permanent shading systems because they generally allow the application of greater and more precise tension.
- Pulley systems are a practical choice for temporary systems as they allow the shade to be erected or dismantled easily and tensioned by hand.
- Snap hooks on the corners can be an advantageous choice for temporary, domestic, or consumer-grade shade structures. They typically cannot achieve the same amount of tension as the others but are the quickest and easiest to take down.
Sometimes, both pulleys and snap hooks are used on the same shade structure. The snap hooks are quick and easy to use while the mechanical advantage provided by the pulley system allows for adequate tension to be pulled on by hand.
There are many important factors to consider when specifying a tensile shading system, but the above points should get you on the right track towards an effective and reliable shade structure.