Wednesday 2 May 2018

Swift boxes in a rendered cavity wall

In a rendered wall, one cannot see the brick structure, so doing a neat job, as in the Cambridge System, is not an option.

[See update at the bottom of this post where we re-engineered the entrances]

Christina Day had 9 Swift boxes in the gable of her house in Haverhill (see here). Circumstances conspired so that she had to move to Lode, leaving four occupied boxes behind. Her new home is a one storey house on the end of a terrace with a gable 6 metres high.

So we inserted 6 boxes in her gable by using a 78mm diameter core drill (acquired from Screwfix) through the render and outer leaf and a 107mm core drill through the inner leaf. The entrance was reduced with mortar to a half-moon 30mm high, with a ramp across the width of the outer leaf.

The 50mm cavity is bridged with a 100mm pipe.

The risks in this project were that we could have hit a wall tie, or the render could have been laid on steel mesh - but fortunately we encountered neither of these.

We did not anticipate that the bricks in the outer leaf would have a 'frog' facing down, leaving holes in the entrance passage which needed making good ('frog' = a depression made in a brick). Nor did we anticipate the state of the inner leaf, with much of the mortar loose, needing substantial repointing.

6 neat holes in the gable
6 installed Swift boxes with a satisfied Bill Murrells
Close up of entrance exterior
Close up of entrance interior
Installed Swift box, with perspex back and cover removed.

Section through computer model
Tool used to fashion entrances

UPDATE September 2018

We are pleased to report that one pair moved in to one of the boxes, laid 2 eggs and hatched 2 chicks. However, we had second thoughts about the entrances after the chicks fell out and were then replaced in the box.

We realised that any chick venturing as far as the conical tunnel entrance would not then be able to reverse back into the box. so it was decided to re-engineer the entrances. This was achieved by drilling a rectangle of small holes around the circular entrance and then inserting a half-brick entrance piece. For this project we used up some entrance pieces made from sections of air brick liner as described here.

A further problem was that, in the long hot summer, the temperature in the roof space reached 42°C, so the chicks were taken into rehab and were successfully fostered by Judith Wakelam. The plan is to install ventilation tiles in the ridge of the roof.

Finally, on inspecting the boxes at the end of the season, 2 other boxes had feathers stuck down to the nest forms, so maybe more pairs will materialise next year. 

6 re-engineered entrances

Close-up of re-engineered entrance

1 comment:

  1. What a great job, creating so many neat homes for swifts.