As architects in one of the most comfortable and beautiful settings in the world, we are big proponents of tensile shade sails in design. Why? With elegant and affordable forms, colors and textures that hover in mid-air while providing temperate spaces to relax and recreate, tensile shade structures have an awful lot going for them. The following is a basic primer on the topic, as well as a case study of a recently realized project.
Shade Structure Basics:
At its most basic level, a shade structure is a design solution that aims to transform and temper harsh outdoor areas into comfortable and usable space. Tensioned from multiple anchor points at a height that is optimal relative to use and solar orientation, shade sails can provide refuge from the sun while preserving nearly all other desired elements of the outdoors – the views, the breeze, and the relaxation. Given Santa Barbara’s fortunate Mediterranean climate and the general desire to spend significant time outside throughout the year, we are often asked by clients to create spaces that preserve the outdoor experience but limit over-exposure to the sun. Tempering the sun and taking advantage of natural light and shadow are site-specific considerations that Blackbird is adept at manipulating for all types of projects.
Shade Sail Materials:
Deceivingly simple in concept – a few steel posts and triangles of fabric stretched taught between them – designing and permitting shade structures like this one can be actually quite complex. Particularly in California where fire hazards are a key component of any code compliance review finding a fabric material that will meet all performance criteria can be difficult.
Shade sails can be made from various types of fabrics that have different strength, appearance (e.g. color and texture), performance characteristics and costs to consider.
At the simpler and less-expensive end is high-density polyethylene (HDPE), which you’ve seen in the form of milk jugs, hard hats, and hula-hoops. For mesh shade sails made from this, the HDPE tensile fabric forms a thin membrane that offers protection for up to 98% of the sun’s harmful UV rays while still allowing air and rain to flow through.
At the mid-level are acrylic and polyester fabrics that have lots of color options and can be treated to have good color-fastness and flame-resistant properties. The weave is denser than the HDPE mesh, meaning that less air and water can permeate through the fabric, though they are not typically fully waterproof.
At the high-end are PVC or Teflon coated fabrics, which are typically used for large structures that need to be fully waterproof and/or fire resistant (such as the Denver Airport Terminal). These are very durable, but can also be significantly more expensive.
Case Study: Crane Country Day School
What seemed like a simple request from our client, Crane Country Day School, to provide much needed shade at their frequently used 1,700 square foot lunch table and outdoor gathering space, was actually a highly technical and challenging design opportunity for our office to solve.
The Design Solution:
When selecting a fabric for this particular project Blackbird took into consideration the user criteria which included a low openness factor (high % shading) and a neutral color – no one wants to eat under a canopy that under-shades, over-shades, or tints the color of the light such that their lunch looks unappetizing (no blue, green or red sails here!) From a code perspective the criteria included compliance with various tests for fire resistance, ignition resistance, flame spread and smoke developed indices. Ultimately, a Serge Ferrari fabric called Soltis 92 was selected for its abilities to meet all the user and code criteria established for the project. This particular fabric is mesh constructed of a PVC coated polyester base cloth that absorbs and reflects up to 92% of the sun’s rays.
Our design for the shade structure steel posts took formal cues from an adjacent Sycamore tree. Arms branch out from several of the vertical posts – resembling tree branches – and allow for fabric sails to stretch past one another to create greater shade coverage. A variety of post heights and fabric connection points result in a more dynamic canopy as the fabric panels twist and angle while spanning between posts. Post heights were also carefully manipulated to increase shade coverage at particular times of the day and year. Posts are lower on the south and grow in height moving north so that the sails tilt down at the southern end and scallop upwards towards the north.
The design process included careful consideration of the site’s solar orientation and the shade coverage provided at various times of the day and year by different design options.
As seen in the animation below, the final design provides almost complete shade coverage throughout the year during the lunch time hours of 11am-2pm. This was a challenge to achieve given the relatively constrained site that limited the possible placement of support posts by existing playing fields and a fire department access drive.
September 21st 11am – 2pm
While several different designs were considered (see images below), the client’s desire for full shade coverage ultimately pushed for the selection of the final design over other options.
The end result is a comfortable outdoor dining room providing 1700 square feet of shaded seating for all to enjoy their lunch.