Crack in pebble dash brick wall where extension joins house

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Would this "downward movement" just be settling of the foundations rather than the dreaded form of subsidence relating to the lack of foundations. Is there a definitive way to tell via observation?
 
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Settlement and subsidence are often confused. Buildings settle when first built. The amount depends on the subsoil. Ideally the building settles evenly, but when it does not this is known as differential settlement and can cause cracking in the structure.
Subsidence is when something like leaking drains cause the problem.
Just by looking can sometimes be tricky, unless there are some obvious possibilities like trees close by in shrinkable clay, or in a mining area.
You may have to dig some trial holes.
 
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Thanks for the reply. The engineer recommended a drain survey so I think I will go with that as he pointed out a tree approx. 2m away from the extension, but it is more of a bush about three foot to five foot high.

What else could it be if the drain survey comes back without any damage?
 
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Could be the extension isn't tied the to house and has just moved slightly. Buildings are always on the move.
 
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I received two new photos of the crack from my engineer. He said that the reason why he thinks it is still moving is that the mastic that was placed into the crack is not as snug as it should be.

Are these comments and new photos a game changer in regards to the cause of the crack?

they are of the bottom of the extension going up to the top.
 
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As well as those pics. it would have helped to see the side of the building as a whole.
 
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The only other pics I have is the one

to the left of the crack is the extension and to the right is the main house.
 
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Is it time to be concerned?
does it look more damp around the bottom where the crack is than further to the left past the crack? Could this suggest pipe damage?
 
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I'm not a builder so this is just my personal opinion.
The house was built in 1936 so it has had almost 80 years to settle, whereas, the extension was built only 2 years ago so I would expect there to be some movement. However, only a detailed examination will tell if this movement has been 'normal' for this time frame. This may involve taking various measurements, historical searches of the surrounding area and possibly bore hole soil samples. Regarding the foundations, or lack of, then any plans submitted to the local authority for planning permission should still be available and maybe even a copy with the title deeds of the house. The building inspector should also have been on site during the construction to make sure relevant rules/regulations were being adhered to. This may help you to decide if there is anything to be duly concerned about.

One other point. If that is concrete rendering below the pebble dashing it could be bridging any damp course that has been installed. It needs to come off.
 
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If the extension was intended to be rendered to match the existing, the outer skin could have been built of lightweight aerated conc. block. That block is notorious for shrinkage, and that could possibly explain the vertical crack, particularly if they used starter strips instead of bonding-in.
See if you can find the plans, and check what was specified for the outer skin.
 
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There is a bathroom immediately off to the right of the crack in the main house on ground floor. The engineer noted a crack on the interior wall of it if that helps to diagnose.
 
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Looks to me like the extension wasn't tied in the the house properly, or at all.
 
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Would that account for the lower crack where it goes off to the right?
 

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