There are a few things you can with your standard langstroth roofs to help keep the bees comfortable during a heat wave. There are also a few design modifications well worth considering when building your own roofs that may further protect your bees from the intense mid-summer sun.
Can't the bees just fan the hive to keep things cool?
Yes, they will certainly try, but as amazing as they are, even bees have their limits. If it gets too hot they will shut down brood production, and in extreme situations it is possible to lose colonies.
To get a sense of how hard your bees are working to keep cool, it's relatively easy to place a thermometer at your entrance(s) to gauge the temperature of the air being pushed out of the hive.
Keep in mind brood rearing requires a temperature in the 33-36°C (91 - 97°F) range. If your entrance temperatures are significantly above that, you may wish to take the temperature near the brood nest to see if they are winning the climate control battle.
Even when things are not too extreme, why not take a few simple steps that might save your bees from wasting time and energy?
Adding an upper entrance and tilting a telescoping cover back is certainly a simple way to offer some heat relief to a colony.
Painting metal roofs white
With the ambient temperature at 33.8°C (92.8°F), a plain metal covered roof was a very hot 46.1°C (115°F), while a metal rooftop with a coat of white latex paint was 38.3°C (101°F):
In my region, it is generally advised to locate your bees in full sun. For those living further south, the conventional wisdom is to try and provide mid-day shade. If, like me, you have chosen a full sun location, you can provide shade only when the temperatures are unusually hot.
A simple, if temporary, way to add shade is to lay a few tree branches on top of your hive. I chose branches from a tree species known to be invasive in my area.
Within a short period of time, this dropped the temperature of my painted roof down 3.4°C to 34.9°C (95°F).
Of course, the leaves will soon dry out and shrivel. If you are experiencing an extended heatwave, you may wish to consider a more durable solution.
Build a double-level roof.
The idea here is that the top-level creates a solar shield that effectively shades the bottom level, while simultaneously creating an air gap through which a breeze can pass, thus minimizing thermal conduction of heat downwards into the hive.
With the ambient temperature at 33.7°C (92.7°F)
The metal covered, upper-level of the roof was 46.7°C (116°F), while the temperature below was a cool 31.4°C (88.5°F)
The inspiration for this style of roof comes from the warré hive.
Build your roofs with corflute under the metal
Corflute is the kind of material election signs are usually printed on. The air pockets in the material help insulate and minimize thermal conductivity.
Use a Quilt or other form of insulation
A warré style quilt helps keep heat in during the winter, but it also helps keep heat from the sun out of the hive during the summer.
The thermometer I used throughout this post is a regular digital thermometer that one might use in a kitchen.
The main quality you are looking for in this tool is ability to adjust to ambient temperature relatively quickly. You can find one here on Amazon.