Rowena decided to take the plunge and install internal boxes in her gable at roof space level, using what has come to be known as the Cambridge System. Two external boxes under the eaves of the same gable, installed in 2015, housed one pair of Swifts in 2016.
Bill and Dick managed to install 3 half brick inserts and the boxes in one day. There is nothing new here, but we are pleased how it turned out. Technical details are:
The half brick inserts were cast in white concrete, then stained red.
The bricks each side of a vertical bond were reduced by 56mm to make space for the insert.
The nest boxes are made of treated external plywood: a simple "shoebox" with internal dimensions W 25cm x L 20cm x H 15cm. Flanges above and below the front of the box are screwed directly into the blocks, which are made of soft vermiculite. The top screws were angled downwards as this is more secure.
A simple hinged door on the back allows for inspection and maintenance.
The PVC pipe has an external diameter of 107mm. The pictures below show how the pipe is trimmed to span the cavity. A slot is cut in the top of the pipe as it is a tight fit. Mortar was placed in the bottom of the pipe to provide traction for the Swifts.
A 107mm diameter core drill was used to make holes through the blocks
|Two eaves boxes and 3 new internal boxes|
The external box on the right had breeding Swifts in 2016. Photo Clive Cooper
|Close up of one of 3 entrances. Photo Clive Cooper|
|Internal box, showing hinged door and simple catch. Photo Clive Cooper|
|Components of the Cambridge System: entrance piece, pipe, nest box and concave.|
|Components in context|