Conifer trees & subsidence

[Sunshine]

Dear ArbTalk Arborists

 

I would be very grateful to hear your opinion regarding 2 conifer trees and the subsidence issues we are experiencing in our flat and the flat opposite us.

 

Both flats are ground floor in a 1920’s building (renovated in 2005) sat on top of London Clay in South West London.  The flats foundations are strip foundations.

 

The flats have plants at the front, which includes two wisteria plants, and two conifer trees at the back.  All planted in 2005.

 

The flats move in the summer, causing cracks to the internal & external walls.  The movement takes place in the corner of the flat where the wisteria plant is planted.

 

During the last years the flank step wall (which was originally hard up against our flat walls) has been sinking and creating a gap of around 4cm currently.

 

My understanding is that trees extract large volumes of water from the soil and during dry hot weather can cause the clay soil to shrink, which can lead to subsidence.  Similarly for the wisteria plant.

 

What is the right thing to do here?  Removing trees and wisteria?  Reducing them in size?  Installing an irrigation system?  Should we factor heave here?

 

I am attaching pictures for you to look at.

 

Many thanks in advance.

 

Sunshine

 

 

Edited December 1, 2021 by Sunshine

[Squaredy]

9 hours ago, Sunshine said:

Dear ArbTalk Arborists

 

I would be very grateful to hear your opinion regarding 2 conifer trees and the subsidence issues we are experiencing in our flat and the flat opposite us.

 

Both flats are ground floor in a 1920’s building (renovated in 2005) sat on top of London Clay in South West London.  The flats foundations are strip foundations.

 

The flats have plants at the front, which includes two wisteria plants, and two conifer trees at the back.  All planted in 2005.

 

The flats move in the summer, causing cracks to the internal & external walls.  The movement takes place in the corner of the flat where the wisteria plant is planted.

 

During the last years the flank step wall (which was originally hard up against our flat walls) has been sinking and creating a gap of around 4cm currently.

 

My understanding is that trees extract large volumes of water from the soil and during dry hot weather can cause the clay soil to shrink, which can lead to subsidence.  Similarly for the wisteria plant.

 

What is the right thing to do here?  Removing trees and wisteria?  Reducing them in size?  Installing an irrigation system?  Should we factor heave here?

 

I am attaching pictures for you to look at.

 

Many thanks in advance.

 

Sunshine

 

 

Surely this is a question for a structural engineer?  Yes trees do take moisture out of soil but those buildings need to be looked at by a qualified engineer or three not tree experts on a forum.

 

That flank wall is clearly a much later addition so clearly built to different standards and using different methods, and maybe not compatible with the older wall next to it.  I think this is quite a complex problem, and may be affected by trees and vegetation, but the fundamental problem needs to be assessed by an engineer on site.

[Khriss]

Do you own that land, or is it someone elses? K

[Sunshine]

No we don't own the land, the flats are all leasehold

[Sunshine]

Squaredy yes regarding the building we have got structural engineers looked at it but they say they cannot comment on the trees as they are not Arborists.

 

Posting on this forum to get opinions on trees, wisteria & flats subsidence.  I know there are very knowledgeable Arborists on this forum and some of them with extensive knowledge on subsidence.

 

For example, I am not an expert but it seems to me those trees are too close to the flats and they are not going to stop growing so problem is likely to get worse.  But is removing them an option or could that cause heave, which is worse than subsidence?  Is crown reduction an option?  Have read that causes the trees to consume more water?

 

Any comments are greatly appreciated as this is causing us lot of concern.

 

 

[Mark J]

1 hour ago, Sunshine said:

Squaredy yes regarding the building we have got structural engineers looked at it but they say they cannot comment on the trees as they are not Arborists.

 

Posting on this forum to get opinions on trees, wisteria & flats subsidence.  I know there are very knowledgeable Arborists on this forum and some of them with extensive knowledge on subsidence.

 

For example, I am not an expert but it seems to me those trees are too close to the flats and they are not going to stop growing so problem is likely to get worse.  But is removing them an option or could that cause heave, which is worse than subsidence?  Is crown reduction an option?  Have read that causes the trees to consume more water?

 

Any comments are greatly appreciated as this is causing us lot of concern.

 

 

You should probably contact your insurance company; if they suspect the subsidence is related to moisture abstraction by vegetation they will engage the services of a suitably qualified arboriculturalist.