Hi. It probably is expansion, so I've based the solution on that. Click this link
http://i9.tinypic.com/4fu566c.jpg and you will find a rough sketch. Scroll around it a bit to get the hang of it. Basically you will have to get the builder to cut vertically down the centre of the crack and rebuild some brickwork to form a vertical expansion joint 1/2" wide. The joint must be filled with 1/2" waterproof compressible fibreboard and the front and any other exposed fibreboard face sealed with non-setting mastic. 4 sliding joints are required in the height of the wall constructed of 12" lengths of 3/8" stainless rod, one end built into and fixed in the wall and the other end left to slide as necessary in a plastic tube. That's all there is to it - done properly you will have no more trouble. Ask away if anything is unclear.