Will removing these cause heave?

[nmjg11]

We've bought a house with a pair of trees in the back garden (Leylandii?) which are very tall. They are also on the southern side of the garden and we're considering having them removed, or significantly reduced to fence height to allow in more light.

 

Shown here taken from our garden, but with our neighbour's in the back of the shot. The closest trunk is about 7m from the corner of our house. It's closer than that to the neighbour's conservatory, but actually their plot (starting the other side of the fence) is a good metre lower than ours.

 

I'd be keen for any thoughts on whether it would be safe to remove these trees, or if we're better off just reducing them right down? 

 

Thanks

 

[bolthole]

This is probably only a big worry if you're on clay soil. Where are you in the UK?

Are there any existing signs of subsidence around the house? Eg. minor cracking around wondow lintels?

Do the trees pre-date the building of the properties (I kind of doubt it, but it's worth an ask!)

[daltontrees]

unless you give a location, no-one can start to answer the question.

[T-Tree]

Hi. I would be interested in hearing the answer to this question for someone in clay soil (East Midlands uk), who does have some cracking around door frames. 

 

[bolthole]

Hi T-Tree,

Clay soil shrinks as it dries out. There's what you see at the surface, which is a big swing between summer and winter, but often clay soil can be very deep and it's the overall moisture content of that which matters. The surface will be muddy in the winter and rock hard in the summer, but deeper down and throughout the whole 'layer' this variability is far less. 

What does happen is that where land is built on, the amount of water that reaches the clay is generally reduced - houses have roofs and hard landscaped area (paths, driveways, etc), which takes water which would have previously gone into the soil away. So overall, it's fairly normal for clay land that's been built on to shrink. It's sort of pot luck but generally, you'll see a bit of settling in a building on a clay soil. This is the lintel cracks I mentioned. 

Houses have gardens and people plant trees in gardens to make them look nice, amenity, fruit, etc... so after the building hapens, there's then a period where people plant trees and patches of this land where those trees go are subject to more drying - especially with very vigorous, quick growing trees, the area around a tree will become drier and therefore the soild around the roots will tend to shrink more, and more quickly.

For example, I have a fairly mature Laylandii near the back corner of my bungalow. We live on a flood plain on deep clay. That corner of the bungalow has a big-ish crack, not a wide crack, but nevertheless noticable. We asked our builder and he says that the rule of thumb is, if you can't get your fingers in the crack, there's nothing to worry about! Not sure about that, but he knows more than me. The ground under that corner has shrunk a bit more than the rest and that back corner of the building has dropped a bit... enough to open up a crack. We have a bit of very mild cracking elsewhere in the property, but this corner is worse.

If we remove this tree, the bit of garden where it was will become 'wetter' again... so the soil where the roots are will expand. Proably all that will happen is that the crack will close up again, because the tree came after the house.

It's quite a complicated subject and if you have any major concerns you should speak to a structural engineer... but if you have a house which is built amongst existing trees, on clay soil, and you remove these trees the soil will become wetter and expand. This is 'heave'. 

Say you house is completely surrounded by trees, and they were mature when you built the house, removing them would make the soil all around your house expand and probably you'd not notice anything. It would 'heave evenly'. Maybe. If you had the same scenario but say two big trees at one corner and you removed them, the soil there would expand and that corner of your house would be lifted and... you'd probably get cracking, or worse.

With the original poster, I'd be concerned about that conservatory - if it was added on after the house was built, and that big old tree is removed, and they're on clay, there might be some heave! Probably the house will be fine... but it might have a bit of cracking already.

Imagine you've got a big gingerbread house and you try and pick it up... if you can get a tray under it you'll probably be fine, if you get your fingers under one corner, it's going to end in tears!!

[T-Tree]

Hi Bolthole! 
What can I say. Thank you so, so much for taking the time to write such a detailed and thoughtful answer. That’s so appreciated. How kind. I have to admit to feeling quite overwhelmed by the amount of work there is to do at the property and I’m also dealing with some sneaky/nefarious behaviour nearby.

 

Your answer makes a lot of sense. There has been some professional advice, though not specifically about heave.
I believe that the house predates the trees. One is taller than the house and the trunk is about 16 - 18 feet from the corner of the building. The garden is terraced with the tree being in a corner bed on the top terrace (patio). The patio is now very uneven throughout, with some big dips. I’m not sure the best course of action to prevent damage. Trees are great for keeping the air clean, dampening noise and generally look good, so ideally I wouldn’t take it out, but it does block a lot of light. I’d like to reduce it but I’m not sure how sensible that is.

Currently other remedial work needs to be done and apparently I should wait 6 months after work on the trees.

I need an project manager 💛

Thank you so much again for your reply. 

[Mick Dempsey]

I’d say almost certainly not. 
Cut it to the yellow line this year, then take it out completely next year or the year after.

[Mesterh]

7 hours ago, Mick Dempsey said:

I’d say almost certainly not. 
Cut it to the yellow line this year, then take it out completely next year or the year after.

I see that you've played choppy conifer before.

 

The top yellow line is where the customer wanted it cutting down to. The next yellow line is where they decided that it really needs cutting didn't down to although they only tell you this once the once the blower has just been switched offand the van fired up. The third and forth line happen within a frenzy of pissed offendnish and the fifth and final like is underscored in red as its the final, thats it, we'll all agree or there's going to be a fight.

 

[daltontrees]

20 hours ago, T-Tree said:

Hi Bolthole! 
What can I say. Thank you so, so much for taking the time to write such a detailed and thoughtful answer. That’s so appreciated. How kind. I have to admit to feeling quite overwhelmed by the amount of work there is to do at the property and I’m also dealing with some sneaky/nefarious behaviour nearby.

 

Your answer makes a lot of sense. There has been some professional advice, though not specifically about heave.
I believe that the house predates the trees. One is taller than the house and the trunk is about 16 - 18 feet from the corner of the building. The garden is terraced with the tree being in a corner bed on the top terrace (patio). The patio is now very uneven throughout, with some big dips. I’m not sure the best course of action to prevent damage. Trees are great for keeping the air clean, dampening noise and generally look good, so ideally I wouldn’t take it out, but it does block a lot of light. I’d like to reduce it but I’m not sure how sensible that is.

Currently other remedial work needs to be done and apparently I should wait 6 months after work on the trees.

I need an project manager 💛

Thank you so much again for your reply. 

I reiterate, unless you say where this is no-one can help. Why? Because in some areas there aren't shrinkable clay soils or persistent soil moisture deficits that could cause subsidence or heave damage. Why worry about these until you know the local soil type?

 

And as usual the original poster has disappeared. All a big fat waste of time.

Edited September 11, 2023 by daltontrees

[Tikay Musiiwa]

I am not a specialist and I can't be sure but there is also a risk when it comes to this subject. The best thing you can do is contact a specialist and see what their thoughts are.