Vertical Cracks in block walls of gable ends in loft

[Grimreaper1]

After having our bathroom refurbished, which involved:
a) knocking off all tiles and render back to blockwork on internal non-supporting walls, as they found they couldn't fit in the bath!
b) kocking out some of the blockwork on an external wall beneath a window for burying pipes for wall hung basin

I then noticed (and they definitely weren't there before) in the loft on the gable end above the window and wall hung basin, a 2mm vertical crack that extends up through about 3 courses of blockwork, splitting a couple of blocks and then following mortar lines. The other gable end has a shorter length 1mm wide crack going through a single block and some of the mortar in a similar location.

Could this have been caused by the vibration travelling through the building of them knocking off the tiles and render - it seemed an awfully hard process? Or structural movement as a result of them chasing out the blockwork beneath the window on the external wall for the wall hung basin? They've cut out more than they should have for the pipes!

Or I guess it could be coincidental, but I'm not convinced! Also had some roof tile/undercloak slippage at same time.

House is early 70's build, inner leaf and partition walls are lightweight thermal blocks

 

[^woody^]

I'm going for coincidental

 

[Grimreaper1]

Thanks but never had probs with cracks before. Checking last night the crack in the gable end above said bathroom extends through the mortar joints up to the roofline and there's movement in the blocks/section of wall to the right of it which is really worrying. When the wall was chased for the pipes for the semi ped the guy said he had to use kango or similar. As I say these weren't narrow vertical chases but quite a large section beneath the window in the bathroom that's been effectively chopped out of the block work. It surely must have weakened the wall?

 

[tony1851]

The lightweight blocks do shrink a lot and crack - you may not have noticed the cracks in the loft before.
(Seems strange to use a Kango on lightweight block, though)