036. Design consideration: window shades

I've mentioned a few times already that it is crucial that a good plan be made for shading the (transparent elements of the) house from the sun in the summer to avoid overheating. Generally speaking, this topic is especially relevant in these times of rising global temperatures and there is a strong effort underway to find the best (low-energy) solutions. Organizations such as the European Solar Shading Organization (ES-SO) have some information in English on their websites[1]. Minergie in Switzerland provides guidelines for good practice. See Figure 22 in Post 29 to get an idea of the size of the problem for our house, as calculated for a particular set of parameters.

The German Institute for Standardization (DIN = Deutsches Institut für Normung) provides a useful listing of the rough efficiency factors for different types of shading systems as given in Table 4 below (visit the ES-SO link to see illustrations of these systems). Of course, the actual numbers will vary with the details of the type of materials used. In general, the best systems are those that are installed outside the glazing. For residential applications, roller shutters[2] seem to be the usual choice over here. Aesthetically they're not my favorite as I find them chunky and obstructive. A better alternative are external venetian blinds, with adjustable louvers that allow a view of the outside. They're rather high-maintenance from a cleaning point of view but WA assure us that in our locality we won't have to clean them more than once every couple of years.

Table 4. Solar gain reduction factors for different window shading systems. Smaller is better. Source: DIN 4108-2

	Reduction factor
Type of shade	Fc
No shading	1
Internal installation or between the glass panes
White or reflective surface with low transparency	0.75
Light colors or low (less than 15%) transparency	0.8
Dark colors or high transparency	0.9
External installation
Rear-ventilated adjustable louvers	0.25
Blinds and materials with low transparency, rear-ventilated	0.25
Blinds, general	0.4
Shutters, roller shutters	0.3
Overhangs	0.5
Awnings, ventilated	0.4
Awnings, general	0.5

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[1] A nice list of the different types of shading systems can also be found at their site → European Solar Shading Organization

[2] Actually, I'm not sure this is the right term for the objects I'm thinking of which are called Rollläden in German