Friday, March 27, 2009

A Passive Cooling Asset: Exterior Retractable Shades

How far can one go improving the cooling properties of one’s house? Whether it’s a remodel or a new house design, it’s an interesting question with a lot of creative answers. Air conditioning is one stalwart solution, but there are other ways to improve the comfort of your home.  It frequently surprises people to hear that “passive cooling” options should really be exhausted before exploring air conditioning.

"Passive cooling" is a term applied to any cooling srategy that uses few mechanical parts. Allowing cool air to flush a house at night while closing up the house during the day, is an everyday example of a passive cooling strategy. Increasing a building’s thermal mass, improving insulation and strategically planting deciduous trees are also good examples.  But exterior retractable shades are another solution.  Because they are simply placed above the window on the outside of a building, they are a flexible solution that can be elegantly incorporated into most floor plans with minimal impact on the homes basic layout.  Furthermore, you can still see through them when they are deployed.  With all these design assets, they represent a highly efficient solution that is wrongly neglected.  

When dropped, exterior shades cool a house far more effectively than interior shades. Living passively does require a certain tolerance of seasonal temperature swings. In the winter a house is going to be cooler than it is in the summer. But if one considers the reduction or elimination of energy use, one starts to appreciate the possibilities. Should we really expect the house to be as warm in the winter as it is in the summer?

The ideas of the Slow Food movement and seasonal eating resonate with our Sonoma County way of life and the architectural parallels are worth exploring. Retractable shades, like most passive systems, heighten your awareness of the outdoor environment. If the building system is too highly processed we lose a sense of where we are. The cost associated with living this way is not sustainable. In a building on a thermostat it’s possible to exist without ever registering the change in the seasons or the character of our natural environment. Good architecture should be about tempering your environment, not disowning it.

The following conditions imply a project that is a good candidate for retractable exterior shades:

• A home with glass that receives a lot of summer sun (i.e. windows that face eastern, western and southern exposure)
• A home where the summer sun shine through a window onto thermal mass inside your home (e.g. a concrete floor or a tiled wall).
• A home that has a potential view that would be desirable in the winter but presents a cooling challenge during summer months.

If you meet any of these conditions consider these questions before installing exterior shades:

• Does your home have sliding or double hung windows on your building? Are you interested in using such windows? Retractable exterior shades work best with sliders and double hung windows because they don’t interfere with the window’s operability. Other windows like casements or awnings can be used but one is sometimes forced to choose between an open window and a shaded window because these window types swing outward.
• What size fabric is necessary to minimize the seams visible in your opening? If you have a large opening, certain screen fabric selections are hard to use without having a noticeable seam in the middle of the field of view. Check out your fabric capabilities before you incorporating it into your design.
• How much transparency is desired for sun protection and privacy? If you have a view you would like to see through the fabric, there is usually a trade off here. Be sure of your priorities before finalizing the fabric selection.
• What color of fabric is desired for sun protection, esthetics and privacy? Is it worth investing in a two sided fabric?
• Should the screen be motorized or manually operated. Motorized shades are an additional expense that can make sense if there are a lot of windows that need to be closed all at once or a particular window that is difficult to reach from the outside.
• Will the screen be mounted in the window opening, on the wall above the window or in the roof eave? This can effect whether your shade will run on tracks or cables. If the screen is mounted on the face of the wall, the shade looks better running on cables. Cables are less obtrusive than the track. If the shade is mounted in an eave space you can avoid the manufacturer’s housing and go with something more integrated by building your own recessed box. Our firm recently did this on a contemporary residence and we found it could be designed to fit into roof visor pretty easily (see figure) and also accomplished a very integrated look.
• Is there a good unobtrusive place to mount a wind sensor? Wind sensors are not always necessary. If the shade is mounted in the window opening, or simply on tracks, a wind sensor is not as necessary. But for a screen that is cable mounted on a wall face, one should consider a wind sensor.
• Do I need my exterior shade to function as a bug screen? This can simplify both the interior look and functionality of a building but it usually works best with a track system. A cable system always has a little clearance around the shade. If you’re serious about your aversion to bugs, this might not be enough protection.

I find many of my clients are surprised to discover they are a lot better off investing in a good passive cooling design than a good passive (solar) heating one. Why? The short answer is that heating a home is considered more of a life safety concern in the United States. Legislation, industry and our northern California climate have joined together to provide you the homeowner with many widely available and effective options in this regard. The same can not be said of passive cooling. Retractable shades are an attractive option.

In many ways exterior retractable screens are doing for a contemporary residence what traditional shutters did for older homes and it can be said that good architecture makes an esthetic out of the human response to the environment.  Exterior retractable shades are an intriguing contemporary response that begs further expression and refinement.


  1. What a cool way to build - I look forward to seeing the project once complete!

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