How big/small a seasonal crack do you worry about?

[SlinkyDogg]

We live in an Edwardian house in London and have a crack near the front door which opens up to about 2.5 mm in the summer but closes completely in the winter.
This summer seems to have been the worst.
I'm not sure if it's the clay soil or the huge tree in the footpath just outside the property.
Should we be worried especially as we are thinking of getting a loft conversion done.
Is there anything we can do about it, like asking the council to cut the tree down and replace with something smaller?

No. Trees drink a huge amount of water. Taking it down will ensure the water stays in the soil and can make it swell. If it’s clay, this is likely. This can cause heave. Cracks tend to be vertical with heave as the walls are pushed outwards by the upward force on the foundations. Door frames can go out of true.

With subsidence, (foundations sinking) cracks tend to be more stepped. However at 2.5m, I would get this crack looked at and I would say the house is moving with ground conditions. The water in the soil in winter closes it up and then it dries out in summer so the crack appears again. Cutting the tree down, even if it’s replaced, probably isn’t a great idea. Contact your insurers.

Thanks Bubbles. I feel quite wary of talking to our insurer just yet.
Who else can you discuss this sort of issue with, a structural engineer perhaps?

Yes. That would be a good course of action. They can advise about the crack and possibly monitor it. My DH is a Structural Engineer (although he doesn’t really do this sort of work any more) but it is worth ascertaining what the problem is before you go down the insurance route. However as I’ve been married to DH for several decades I do know that cutting down a mature tree is risky as I described above. Another issue could be tree roots. Are they interfering with the foundations? This is why you need a professional to look at the whole situation.

Yes, it could well be the roots as some summers the tiles in our front garden path start to lift.

Or it could be water retention in the soil due the excessive rain we have had. The tree possibly isn’t drinking all of it. Uneven paths is a sign of heave but again, get advice to decide how to proceed.

Sounds like the tree needs reducing in size but it needs to be done slowly to stop heave