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Building Homes or Extensions/Cracking in exterior extension wall


Hi Martin

When there is stepped cracking (4 mm wide)in the mortar at the point where a brick built  extension joins the original house - should we be concerned? The extension was built more than eight years ago and the cracking runs vertically from the top of it to the bottom. Someone has attempted to repair it previously by putting silicone down the length of the crack.

It sounds like a settlement crack. This is caused by the weight of the new extension gradually compressing the ground beneath, causing a small amount of movement. If it is settlement then there is no need to worry. Silicon will seal the joint, or alternatively you could repair it with mortar. Other signs to look out for are uneven floors, and signs of movement in door or window openings, which could indicate a more serious problem.

You should monitor the crack to make sure the building isn't still moving and if you are still concerned get a surveyor to take a look at it. Settlement is very common in extensions. It rarely causes any serious problems.

Building Homes or Extensions

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Martin Owen


Anything relating to the design and construction of extensions and loft conversions.


I currently work as an Architectural Technologist for, where I design extensions and advise on legal implications.

Degree in Architectural Design and Technology

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