The disadvantage of using metal roof is, it absorbs heat and transfers the heat into the Bh. Due to cost and easy installation we have no choice but to use them.
I have seen many Bhs roofing using metal (zinc) and theirs internal environment goes hare wired. Making records of 36-40C during hot weather and when it rains it drops below 28C. In such condition I wonder which type of Swiftlets would stay. None!
It’s not that metal roofing can’t be used or totally should be avoided. It can if you know how to make use of it. If the ceiling material below the metal roofing is of 2x4’ ceiling board and not concrete then insulation material has to be put beneath the metal roofing. This is to reduce the heat absorbed by the metal roof from penetrating into the Bh
Normally many would put 2-4” thick Styrofoam on the top of the ceiling board inside the ceiling. It would help further if an insulation material is being put directly under the metal roof. So there would be double insulation, one beneath the metal roof and another one on the ceiling boards.
If there is no insulation material beneath the metal roofing. The temperature at the air buffer between the metal roof and the ceiling remain high. As the pressure increases during hot weather all hot air would be pushed into the Bh thru the gap of the ceiling.
To reduce the temperature in Bh many resorted to using Humidifiers, water sprinklers,etc to cool down the Bh’s internal. Its neither works as the internal of a Bh is a an closed area. Unless all doors or ventilation holes are opened up so that fresh air could be drawn into Bh often by doing this the whole internal environment is jeopardized. At the end you may get a cool Bh with good temperature reading but with birds staying or make nests.
To avoid this, make sure insulating materials are put beneath the metal roof and then hold them with ceiling boards. By doing this it could reduce the BH’s temperature by at least 25% or more.
A good Bh starts from the moment its constructed not after it has been constructed.
Good Swiftlet farming All!