Gap in Join of Extension and Original Wall

[Maisiemeg]

Looking for some advice please.. A gap has developed where the walls of the original building and the extension meet. It has got progressively worse with the current spell of dry weather. Not sure who I need to get to look at this? Do I go straight to a builder or need a structural engineer or some such first. I would also like to have some idea of what remedial works are likely to be required if anyone has previous experience of similar problem.

I see nobody has replied yet..

You need to go back to the builder and if they dont have a resolution or you dont trust the direction the conversation is going you may need a structural engineer.

If you had any independant design or planning advise you may ask for their professional opinion too.

Plus check if the building works were subjected to building control inspections.

Firstly the good news is it may just be normal settlement cracks.

Your house and your extension weigh different weights. Think a full cup of tea and a half cup placed on a big sponge at the same time the full cup will compress the sponge more.
However in your situation there was a full cup of tea on the sponge you added an empty cup and began to fill it so the area under it will be squished at a slower rate and the cup may tilt a little as originally the one area near the house was already squished by the full cup so settlement makes the new part appear to pull away from the old part.
Its "normal" subsidence.

You can get subsidence monitoring tools which will track the distance and speed at which the gap is opening.
(This method is equivelant to screwing a screw on either side of the gap to get 2 fixed points and measure between the points at regular intervals)

If its not normal settlement you are looking at methods of underpining and mechanically bolting the new part into the older part.

The health warning, the gaps shoud be small if the cracks are in the same place internal and external, if windows or doors are (suddenly) sticking or window glass cracking I would go straight to an independant engineer.

Did the builder have insurance?

Thank you for responding. The extension was built before I moved here, over 20 years ago so it's not a case of getting back to the original builder. When you say an engineer are you referring to a structural engineer?

If its moving after 20 years + I would go with a local subsidance company who should have the equipment to do a survey and monitor.

Few things
Have you checked that your drains and sewage pipes are ok?
Any chance there was an oil leak near the foundations in the past?
Have you checked your insurance policy for cover as sometimes you have to use their approved company list

I have detected no issues with drains and do not believe there has been an oil leak. I will be checking insurance. Thanks for the guidance

A “subsidence” company is a structural engineer. Do go with one that’s actually qualified - CEng MIStructE.

Its probably differential settlement. The extension might have different foundations. You could see if local building control had the design details of the foundation. However an engineer will tell you what has happened.

It does sound like subsistence, but it may be relatively minor. If the ground is very clay based combined with the dry smell then some houses are suffering minor stuff like this. If you went to your insurers would probably go into a monitoring phase. However, it then becomes very difficult to sell your house.

We had this years ago with a conservatory during a dry summer. Insurance company diagnosed subsidence (we were on clay) and employed builders to add extra ties to the walls and re-plaster. We also had to get rid of a large Eucalyptus tree which was suspected of adding to the problem. All passed as OK 12 years later by surveyor when the house was sold.

@Maisiemeg

Unless you have split bricks and obvious cracks in the walls, it’s probably not subsidence. If it was, almost certainly both section of the house would be affected. The extension is probably designed to move differentially to the rest of the house. This actually prevents serious cracking. But do get it checked. If there are cracks in bricks then that’s more serious. I would not contact insurance just yet. I would pay for a structural engineer first and pay. They can then advise if you need to go to your insurance for repairs. They will advocate for you if your insurance co is difficult.

Thanks everyone for your input. There is no cracking to the bricks on either the extension or the main building - it is purely the join where the bricks were butted against each other, rather than tied in. It is built on clay which I suspect is much of the problem, with the dry weather. Think I will take the advice of TizerorFizz and not go to the insurers in the first instance, but will seek a local structural engineer instead.

Friends had this, surveyor monitor then ties employed. It's still standing decades later.

Most buildings will be standing after movement. Very few collapse in this country.

The reason why the bricks are not tied in @Maisiemeg is to ensure each section moves independently. This prevents bricks cracking as each section can move independently. It’s like rail lines with movement joints to prevent buckling. Get a report to put your mind at ease but if bricks are not cracked you are probably ok.