One corner its closed at the bottom then as we go up it cracks around 3mm further up its goes to 5mm along the top and in the corner its around 10mm away from the original building as you can only see mortar on 1 side.It's hard to tell from the videos. If it's a consistent width line from top to bottom then it's shrinkage so nothing to worry about.
If it's closed at the bottom and widens towards the top then the far end of the extension has sunk, so the whole thing has tipped away from the original building. This may or may not be a problem, depending on the extent and whether the foundations are on subsoil or topsoil.
Check for signs of sinking at the far end of the extension. If it's severe to the extent that the brickwork and floor are out of level then there's definintely a major issue. But I doubt it's that severe, I've seen a porch that had a 2" gap at the top of the joint to the original building.
can see any on the wallpaper not can i see through the plasterboards or joists?Any cracks inside?
Looks like shrinkage to me...
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