Any structural engineers? Potential heave/subsidence problem.

tipsychick

I just wondered if anyone here is a structural engineer and could give me some advice.

I live opposite a 70 foot-ish mature oak tree, owned by the local council and right on the edge of my opposite neighbour's garden. I'm probably about fifteen metres away from it, with a road in between. The closest house would be the opposite neighbour's and the tree is no more than five metres from his property. The soil is London clay.

Apparently my opposite neighbour complained to the council a few months back about the tree "smelling". (No other neighbours have smelt anything though). The council have now done some kind of expensive ultrasound test of the trunk, deemed it to be infected with a fungus making it unsafe and the tree is marked for imminent felling. The tree looks absolutely beautiful, is probably a hundred years plus old (pre-dating the houses which are 1930s) and has no outward signs of infection - leaves, branches, etc. all healthy.

This is purely supposition on my part but the oak tree is bang slap in the middle of the opposite neighbour's driveway, which is making parking their three cars pretty difficult (particularly as his eldest has just learnt to drive) and I imagine he is keen to remedy this by paving over the whole garden.

None of the surrounding neighbours are too thrilled at the thought of subsidence/heave, etc. and we have a meeting with the council's head tree honcho tomorrow. (He has said that with the road in between, our side of the road is unlikely to be affected but obviously we don't know for sure).

I'm keen to find out if there are any specific tests the council could do to map the spread of the roots and at least ensure they're not under our place or the adjoining neighbours. Anyone got any ideas?

(I've made sure we've definitely got subsidence/heave cover in place on our insurance!)

I've posted on the DIY board too, so please do merge/delete. I'm hoping this is where all the structural engineers hang out!

DVardysShadow

So what do you want? The tree chopped? or left to stand?

tipsychick

I'd prefer it be left standing personally. The bark, branches, leaves, etc. all look incredibly healthy.

As a non-expert, I think the chances of subsidence/heave are much greater than it suddenly falling over in a storm but if it must come down, as is the council's current position, then I'd like it done with as much forethought to minimizing subsidence/heave as possible!

lincroft1710

It's more usual for a tree to cause subsidence problems while it is standing, rather than after it has been felled.

g_attrill

lincroft1710 wrote: »

It's more usual for a tree to cause subsidence problems while it is standing, rather than after it has been felled.

Apparently the extra water caused by the tree not being there (to soak it up) can cause clay to expand (heave) and cause problems.

However from what I've read, it sounds like it's far enough away to not be an issue. The neighbour is far more likely to have problems.

tipsychick

lincroft1710 wrote: »

It's more usual for a tree to cause subsidence problems while it is standing, rather than after it has been felled.

I guess it is more likely then to be heave that we get once the tree is down. The tree roots will no longer be sucking up the water and so it will collect, causing the ground to swell and affect our properties that way. As a layman, the damage to properties from heave/subsidence seem quite similar to me.

I'm hoping as we haven't had subsidence to date, then we won't have heave in the future!

lincroft1710

I agree that removal can cause problems, but I've come across more cases of standing tree causing subsidence/heave.

tipsychick

g_attrill wrote: »

However from what I've read, it sounds like it's far enough away to not be an issue. The neighbour is far more likely to have problems.

That's really what I'm hoping for us, particularly with a road in between which will have it's own foundations, plus all the usual utilities, drains, etc.

The tree is pretty close to our neighbour's property. Certainly it would have been close enough to put me off buying because of that. Their front garden/driveway is dominated by it and I imagine it must be quite gloomy inside because of it.

jenny74

lincroft1710 wrote: »

It's more usual for a tree to cause subsidence problems while it is standing, rather than after it has been felled.

More usual, but not exclusive. A large tree that is cut down has the potential to cause a substantial degree od subsidence. This is because the roots will rot and shrink, and somethingwill fill the void, usually from above. Hence damage being caused by the land heaving and the property subsiding.

I agree, it does sound as it OP is unlikely to be affected though.

If I were op, I would try to get the council to get a second opinion on the condition of the tree.

Jenny

tipsychick

jenny74 wrote: »

If I were op, I would try to get the council to get a second opinion on the condition of the tree.

I think this special ultrasound scan that detected the fungus was a second opinion, or at least it was done by an outside contractor at some cost to the council.

I will definitely be urging more/different opinions tomorrow though!

I'm so relieved that the consensus seems to be that we're less likely to be affected. I'm not sure that it's going to do much for the value of my property if the opposite neighbour does have problems!