Sunscreen / by keith messick

Here in Southern California the weather is generally good.  Most days are sunny.  In many of my projects, I use numerous, large windows.  This, however, can pose some problems when it comes to managing the heat gain from the sun.

The north and east sides of a building are usually not an issue.  It is the south and west sides of the building that must be addressed.  The easy answer to this problem of heat gain due to the sun is to simply turn on the air conditioning.  Unfortunately, this is not an economically or environmentally wise decision.

A better solution involves selectively blocking out the sun at those times of the day when the sun is shining through those affected windows.  Window coverings, such as drapes, horizontal and vertical blinds, are usually selected for this purpose.  Most commonly, these coverings are hung on the inside of the window.  


Exterior vs. Interior Shading Systems


Exterior shading systems have a big advantage over interior systems: they significantly reduce unwanted solar heat gain by eliminating one of the sources of that gain. Solar radiation is absorbed by shading material, whether installed inside or outside a building. The short-wave solar energy that is absorbed by the shading system is converted into long wave energy (i.e., heat). With an exterior system, this heat is radiated outside the building and never reaches the glazing. However, solar energy that is absorbed by an interior shading system and is then radiated as heat is trapped inside the building. An effective exterior shading system can block 90 percent or more of solar gain. This can contribute to lower HVAC demand, which in turn can contribute to a downsized HVAC system, lower capital costs, and lower operational costs over time.

Excerpt from AIA Course: Understanding the Benefits of Interior and Exterior Shading Systems


Trees are a great, natural way to keep the sun off of buildings, and reduce the heating effect of the sun's radiation.  If we can keep the sun off of the glass, the radiation of the sun will not enter the building and heat up the interior spaces.

Thus, the best place for the window covering is on the outside of the building.

West Elevation-Note exterior mounted sunscreen on southwest corner

The illustration above is the concept for the Front Elevation of the Skyline Project.  There are large windows on the southwest corner of the residence.  This is the dining room and these large windows make the space light, bright, open, and extremely pleasant.  But the sun light in the mid-to-late afternoon must be controlled.   

By placing a sunscreen on the southwest corner of the building, we are able to use multiple large panes of glass, eliminate interior window coverings, and still control how the sun enters the space.

Southwest Corner

Below are the construction drawings for the south and the west faces of this part of the building.

South Elevation

West Elevation

The sunscreen used here was designed using electrical struts and the variety of connectors and fittings available.  The manufacturers of these products have, apparently, adopted a standard for the sizing of the parts and pieces.  They are all interchangeable.  There are also private label copies of the parts found on Ebay.  Listed below are a few of the manufacturers of these struts.

POWERSTRUT Top_logo.png

Shown below is the detail of how these various parts were assembled to create the sunscreen.

Detail - Sunscreen

The final version of the sunscreen used Powerstrut struts and fittings and 1x4 redwood slats.  The slat material could have be made from wood, frosted glass, steel, steel mesh, composite, or fabric.  However, the choice of slat material will effect the design.  For example, redwood was chosen because it was readily available and was very light weight.  The weight of the redwood on the structure was almost negligible (compared to the weight of the struts, fittings, washers, and bolts).  If glass was chosen as the strut material, it would be significantly heavier and would have structural implications.

Shown below is a mock-up of the bracketry used to support the slats.  The connector that attaches the strut to the house was installed during framing and waterproofed prior to stucco.

The assembly is simply a group of parts that are readily available off the shelf.  It's a bit like building with Lego's. While there are a limited number of configurations, enough parts / pieces are available to make what you need.

Below are images of the struts, fittings, and slats as construction took place.

Initial layout of brackets-Lower strut

Initial layout of brackets-Upper strut

The brackets are initially bolted to the struts. After all the brackets are properly spaced, they must be aligned vertically.  

Test struts

Above, a few struts are fitted to the brackets to verify that everything is in alignment.  A drilling jig was created to ensure that the location of the holes for the bolts will be consistent and repeatable.

Finally, the redwood slats are stained, drilled, and bolted onto the strut brackets.

Note that there is about 10 feet between the top and bottom mounting bracket.  A 1x4 slat was used, as opposed to a 1x6, to minimize the twisting that could potentially occur with wood.  The large surface area on the bracket firmly clamps the slat and keeps the wood straight, countering the natural tendency of the wood slat to twist or curl.  If the wood was straight at the beginning of the assembly, it remained straight.  If the board was warped or twisted badly before assembly, the clamping would only partially straighten the slat.  There were about 4 slats that will be replaced due to curvature.  

Alternatively, another strut and bracket(s) could have been utilized half way between the top and bottom, eliminating the possibility of twisting.  A threaded rod (All thread rod) could also have been used at the midpoint of the slat.

The sunscreen-almost complete - A few curved slats have yet to be replaced.

From the interior-The sunscreen reduces the sun by 50% - 75%, depending on time of day and time of year.