Bat boxes are something we have a lot of inquiries from clients about .
The type of bat box to use will depend on what species of bats you need to provide for or want to attract. Brown long-eared bats will prefer boxes with large cavities, whereas pipistrelles prefer flatter boxes that they can squeeze up into. Maternity roosts will often look for much larger boxes or in the case of Brown long-eared bats the use of roof spaces or attics.
However clients also want bat boxes to look pretty and fit the style of the house.
Many bat boxes are designed more for modern architecture than a renovated building. For example Schwelger [http://www.schwegler-natur.de/index.php?main=produkte&sub=fledermaus ] have the biggest range of “concrete” boxes and their very helpful website contains pictures and specifications for what they look like in reality and how to fit them. The bigger ones are surprisingly heavy and nearly the size of a postbox, an important consideration for aesthetics and safety. They are widely available via resellers in the UK.
On buildings where appearance is very important, especially listed buildings, built-in bat boxes may be a better option. Soffit boxes are a possibility and bat boxes can also be built into walls, where there is sufficient thickness or a double skin arrangement with a wide enough cavity. Both these options leave only a small external access slot, which looks a bit like a letter box.
Wildcare stock a wide range of bat boxes and can send you a very nicely illustrated catalogue quickly by post : http://www.wildcareshop.com/product/nest-boxes-artificial-habitats/bat-boxes.html
You may also wish to consider installing bat access tiles as an alternative provision for bats.
[Footnote : Liz from the Sales Team at Wildcare has told us there is a wider selection of Schwelger boxes on their website than in their catalogue at the moment if you want something specific. ]