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Case study: external shade design for a skylight

In Dec 2021, I paid a visit to Debbie and Brendan, who were seeking some eco-effective advice for a major renovation they had planned for their home in the southern suburbs of Perth.

Part of the renovation included a new kitchen. It was very important for Debbie and Brendan to have as much natural light as possible in the kitchen, as well as good solar passive design to help keep it warm in winter. Unfortunately, because of the layout of their existing floor plan, the only viable way to get natural light into this space was via a skylight in the roof. 

While skylights can be a great source of natural daylight, in summer they can be problematic. Because the sun is almost directly overhead in the middle of the day summer, this can cause excessive solar radiation to enter via the skylight, which can cause a building or home to overheat in the summer. Even though some high quality skylights are made with double glazing, this doesn’t help to prevent excess solar radiation, as double glazing only really helps prevent heat gain & loss via conduction. Some skylights also offer an internal blind or shade, and while this can help, it really is more effective to stop the summer sun from reaching the skylight in the first place. 

I recommended to Debbie and Brendan that they also install an external shading device over the skylight. By designing the external shading device with fixed louvre blades set on the correct angle, this can block the overhead sun in summer, while still allowing beneficial, solar gain and natural daylight during winter. Here’s the sketch I produced for them:

A quick sketch which I provided to Debbie and Brendan to help with the design of the external shading device for their new skylights.

Fortunately, the skylight was positioned on the north facing hip of their existing roof. As you can see, the optimum angle for the louvre blades is 34 degrees from the horizontal, which matches the solar azimuth at around noon on June 21st (the winter solstice). Note this angle will vary based on latitude, though interestingly the roof pitch doesn’t have a significant impact.

I was really pleased when Debbie emailed me a few weeks ago with photos of the finished skylight and external shading! As you can see in the photos, the louvres still allow winter sun to enter the kitchen, and also help to provide a diffuse level of natural illumination during the day. I’m look forward to seeing more photos from Debbie and Brendan in summer, where we should see some effective shading that will help to keep their home cool, while still providing lots of natural light. 

Debbie advised their builder allowed a provisional sum of around $5,000 ex-GST for the fabrication and installation of the shading device. Looking at the photos, it looks like it has been fabricated from hot rolled steel and has a powder-coated finish; this seems like a reasonable price given its high quality construction. 

Many thanks to Debbie + Brendan for the photos!



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