How to Counteract Weight in Fabric Shade Structures

One of the greatest advantages of fabric shade structures—especially in temporary applications—is their low overall weight.  This makes them easier to assemble, quicker to take down, and simpler to transport. Still, weight can be a problem.

Consider a fabric awning.  It’s tougher to cantilever a (heavier) metal awning and extend it far beyond the wall where it’s affixed.  However, even a few extra feet of extension on the fabric awning can dramatically increase the weight felt at the attachment point. This is due to the exponential impact of structural weight as it moves further from the fulcrum (the cantilever).

Fabric is also, by nature, not self-supporting or rigid.  Carrying the weight of the fabric is not unlike carrying someone who’s gone “dead weight” in your arms.  The weight of fabric shade structures must be properly distributed to counteract the natural pooling effect of soft goods.  Without care, the fabric will drape towards the lowest point and focus its weight on the highest point—which may or may not be designed to hold such weight.   

Here are a few of the ways this is commonly handled:

Frame-Supported Fabric Structures

Many engineers turn to a supporting frame of steel, aluminum, plastic, or wood, which can make tensioned fabric structures stronger by giving them a defined form. Common frame-supported fabric shade structures include umbrellas, pop-up tents, temporary garages, and other stand-alone shade structures.

A skeletal frame structure will support the weight more evenly than poles or posts.  Wind can still complicate things, though, as seen in this diagram:

Screen Shot 2020-03-10 at 4.48.55 PM

(Source: ISO)

The issue here is that suction from the wind will tug on the structure’s leeward side, lifting the cover and focusing stress on the end trusses and fabric.  Shock loads from loose, whipping fabric can rip it or damage the load-bearing structure.

This is often solved by using overlapping, paneled fabric (rather than a “mono-cover”), building in hypar, or securely fastening the fabric to the frame at short, regular intervals (to reduce the “parachute” effect).

Counterweights

Since fabric structures are relatively lightweight, it’s often critical to anchor them and give them the weight they need to remain stable.  In other words, to counteract the absence of weight. One example would be the “circle shade” by Eva Jensen Design:

Screen Shot 2020-03-10 at 3.32.23 PM

(Source: Eva Jensen Design)

Counterweights like these—also common in freestanding hanging umbrellas—prevent disruption of the fabric shade structures from wind, weather, collisions, and gravity.

It’s also possible to use counterweights to support the weight of the fabric shade structure itself.  Check out these aesthetic sail shades with hanging counterweights that help the shades extend across an atrium space:

Screen Shot 2020-03-10 at 3.29.37 PM

(Source: ArchDaily)

Tensioning Hardware

Turnbuckles, snap hooks, and pulley systems are commonly used to tension fabric structures.  Tension prevents the fabric from flapping or catching wind—critical to stability. However, tensioning hardware can also support the weight of the tensile structure design itself.

Cantilevered awnings might use a cable-tensioned or rope-tensioned “guy line” to support the weight of the structure, as in this canopy exhibited by Archie Expo:

Screen Shot 2020-03-10 at 3.51.39 PM

(Source: Archie Expo)

The advantage of guy lines is that there are no posts to interfere with movement beneath the cantilevered fabric shade structure, yet they’re strong enough to act as a permanent load-bearing solution.

Eliminating Rope Creep & Sagging

Some modern synthetic ropes are fifteen times stronger than steel, lighter weight, gentler on hardware, and won’t rust, rot, or absorb water.  This can make them an attractive alternative to steel cable in pulley systems and as tensioning lines.

Rope “creep,” or unrecoverable stretch in rope, can be a problem, however.  Some stretch is useful for creating balanced tension, but the gradual lengthening of lines can cause sagging.  The level of creep would depend upon load, ambient temperature, and the exact properties of the chosen synthetic fiber. 

The ideal ropes for fabric shade structures will exhibit a low tendency to creep.  For example, Ocean 3000 is a reliable choice because it’s made from SK-75 Dyneema.  At an average temperature of 77F, with a 7:1 safety factor, SK-75 will exhibit virtually no creep in 24 hours, and only 1% in 100 days.  

Consult with an expert for advice on selecting ropes or hardware that are ideal for your shade system.

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