Saturday 17 February 2018

Cambridge System in a timber frame gable

In 2017 we were alerted to a situation in Isleham where a garage was about to be demolished while there was still a pair of Swifts feeding a chick in the roof. Confronted with a large steel ball, we took the pragmatic (though possibly illegal) approach, of removing the chick for fostering, which was successfully accomplished by Judith Wakelam.

The garage was demolished to make way for a new development of 4 houses, providing 5 suitable gables for Swift boxes. The company hired to assess the environmental impact detected 1 bat leaving the garage, but did not detect the Swifts.

However, the enlightened developer was more than willing to install 10 Swift boxes, 2 in each gable.

The building is timber frame, similar to the Fulbourn internal nest box design. but different from anything that we have previously tackled.

The structure of the walls behind the gables in the roof-space is: brick 102.5mm, empty cavity 50mm, silver-coated plywood 9mm, studs (4" x 2”) 100mm. There is no insulation.

It may have been possible to embed a suitably chosen Swift brick in the outer wall (provided it was less than 152.5mm from front to back, but we chose to recommend a version of the Cambridge System. This is a low cost simple way of accommodating Swifts by securing a nest box inside the roof space between the studs, flush with the plywood.

It comprises:
A half-brick entrance piece: the bricks either side of the entrance piece need to be trimmed by 56mm to leave a space122mm wide.
A piece of nominal 4” pipe, ~115mm long, trimmed to fit in the outer leaf
A simple plywood box, with no front, outside dimensions w350 x d162 x h150mm
A concave nest platform, glued to the floor of the box.
A nominal 4 inch hole is required in the plywood

The box is secured with battens across the studs..

Model of the outside

Model of the inside


System components
2 installed Swift boxes and 1 bat box. Photo Judith Wakelam