Window Sun Heat Potection Screens

To cope better with heatwaves during summer, I was looking for a way to protect the south-facing windows from the heat of the sun. These were the requirements I had for such screens: (1) Protection from the sun heat, (2) yet still somewhat transparent, (3) mounted on the outside of the window, (4) removable and (5) reusable, (6) aesthetically pleasing.

To be efficient, any sun protection always needs to be on the outside of the window. Curtains or screens on the inside will block the direct sunlight, but by doing so are taking up the heat and then simply act as radiators.

In the year before I was using this semi-transparent sun protection film, which is applied directly onto the outside window glas, and was very happy with the effect. However, when it is getting colder outside later in the year, it is necessary to remove the film again, to actually utilize the heat of the sun to warm up the house. Yet, when taking off this film, it crinkles and at least I did not find a way to use it again.

Thus, I was looking for a different solution to make window sun heat potection screens and decided to go for sun protection mesh fabric, which was to be attached via velcro to the outside of the windows (in a very similar way like those magnetic insect doors).

Tools:

- Sewing machine

- Pin needles

- Tape measure

- Scissors

- Lighter or candle

Material:

- Mesh screen fabric

- Velcro hook & loop fastener adhesive tape, white, 19 mm or similar

- Grosgrain ribbon, black, polyester, UV-resistant, 20 mm or similar, should fit to the velcro

- Yarn, black, polyester, UV-resistant

The mesh screen fabric was not easy to source. It needs to be non-stretch and UV-resistant, the mesh material for clothing is not suitable. Something like the mesh fabric used for car window sunshades. I was trying to get it by the meter, but did not find any online. In the end I was getting the pre-cut 'flexible sun protection' screens by GARDINIA for this project. A similar fabric by the meter would certainly have been cheaper, so if anyone finds a source, please share it in the comments!

The hook & loop fastener adhesive tape should be of good quality, as it will be exposed to the weather, with heat and rain. I chose white, as the hook side of the tape remains on the (white) window frame when the screen is taken off.

For the yarn, I chose a slightly sturdier version than the yarn used for making clothes.

Measure the dimensions of the glass surface of the window. We will add some to the top and to both sides for the velcro, yet not to the bottom: To the height add 2.5 cm, to the width add 5 cm. Then cut this from the mesh fabric.

Stick the loop side of the velcro tape to the top of the mesh fabric. Start on one side and continue until you reached the other side, then cut the tape. Keep the film that was covering the glue side.

Use the film that was covering the glue side of the velcro tape from the previous step as a measure, and take a similar length from the grosgrain ribbon. Add about 5 mm. After cutting the ribbon it needs to be sealed to prevent it from fraying. I did that by carefully (!) bringing a flame from a lighter or a candle next to it and melting the fibres at the end.

The grosgrain ribbon is placed on the other side of the mesh fabric, so that the mesh fabric is sandwiched in between the velcro tape and the grosgrain ribbon. Use a pin needle to hold it in place.

Using the sewing machine, join the velcro, the mesh fabric, and the grosgrain ribbon together. For that I made a seam all around, and added a Box X stitch at the two ends. (My first project with the sewing machine, so please excuse those far from perfect stitches.)

Repeat steps 2 to 5 for the two sides of the mesh fabric. It is not necessary to attach velcro to the bottom.

When the loop side of the velcro tape is firmly attached to the top and the two sides of the mesh fabric, the hook side of the velcro tape can be attached to the outside of the window frame. Use the mesh fabric to estimate where the tape has to go, cut it to shape and attach it to the window frame.

Attach the mesh fabric to the window, with a slight pull to have it stretched out. The two full-frame pictures are before and after attaching the sun protection mesh fabric (there is also a mosquito net in front of the window). And there is also a picture how it looks from the outside (please ignore the white net below the window, that is unrelated).

I did a test run on a double window to get an idea of the sun heat blocking efficiency of the mesh fabric, with the mesh fabric attached only on the left window. I then closed the curtains and waited for about 10 min before I took three temperature measurements at different spots to see how much the curtain did heat up due to the sun:

- As a reference, on the side of the window, not hit by the sun: 30.5 °C

- Behind the right window without the mesh fabric: 40.6 °C

- Behind the left window with the mesh fabric: 33.3 °C

Compared to the reference, this yields a delta of 10.1 °C without protection, and a delta of 2.8 °C with the sun heat protection installed, resulting in a 72% reduction in delta.

(Test done end of June, 10:25 am, sunny conditions, outside temperature: 27.6 °C)

In this second test I measured the temperatures of the wooden floor:

- Shadow of the window frame, not hit by the sun: 26.4 °C

- Sunlight coming through the open window: 35.3 °C

- Sunlight coming through the closed window, with the mesh fabric installed: 27.2 °C

(Test done end of July, 10:15 am, sunny conditions, outside temperature: 23.3 °C)

While this is obviously not a completely fair comparison, I think it is still impressive how much of the sun heat is kept outside by the mesh fabric!