Monday, 22 July 2013

Temperature experiment

It is generally thought to be not a good idea to place Swift nest boxes in direct sunlight. But this experiment shows that acceptable temperatures can be maintained in the sun.

by Dick

With the recent hot weather, I thought it worth rerunning an experiment I did a few years ago by making a direct comparison of a John Stimpson Zeist box, made of 12mm plywood, with one modified with an additional roof. I replaced the original roof with a close fitting piece of ply, then I spaced the original roof off this by using 3 strips of ply. I didn't bevel the new roof, as it conveniently provided 2 small triangular ventilation holes. I then painted it white. Both boxes were placed side by side in the sun and 2 max-min thermometers were placed inside at the ends furthest from the entrances.

The boards on top of the boxes are intended to simulate the shading effect of narrow eaves.
A view end on, showing the additional roof and air gap.
And the result is that the additional white roof reduces the temperature by up to 5°C. On 3 different days, I recorded maximum temperatures of 31.8 vs 37.0°C, 36.8 vs 42.1°C and 34.6 vs 38.4°C.

Part of this effect is the white paint - it certainly feels a lot cooler than the unpainted wood, and part is the shading effect and the air gap between the 2 layers of plywood.

The additional roof not only defends the box from the sun, but also from the rain, which is important for a wooden box.

We actually described this idea some years ago here and here


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