Heave / subsidence from oak on clay soil

[joepatr]

Hi all

 

I’m based in North West London (an area with shrinkable clay subsoil) and currently have an oak tree in my garden, approx 6/7 metres tall. 

 

I’d like to have this taken down eventually but am obviously concerned about the risk of not only subsidence but also heave. 

 

Could anyone recommend the best way to manage this to ensure ensure the safety of my property? I was thinking the best way would be to have the tree slowly reduced over a period of time before having the stump totally removed. 

 

Would this be the way forward, if so, how much and over what period? I was thinking taking it down in quarters over the next few years but one of the local tree surgeons suggested thirds every couple of months. 

 

I’d be grateful for any suggestions and also any companies in the Hillingdon area who could help. 

[Mark2]

Clearly this tree and your house have got on fine for a long time with no problem ! 

From the little we can see, it looks to have been well maintained! It also looks ‘of value ‘ in that area as there are few trees to be seen in photo.

How long have you lived there? And why do you want to remove it ?

conclusion—- strengthen foundations and regular maintence of tree !

[Chris at eden]

1 hour ago, Squaredy said:

 

 Your risk as you say is heave not subsidence, but equally destructive.

Why would you think that?  Subsidence is way more common than heave.  If the tree continues to grow then the subs risk will increase. If the frequency and length of droughts continue to increase then the risk of subs will increase. 

 

Then in again the house could have sufficient foundations. A lot of old houses have cellars. It’s difficult to say without the facts but the situation where heave is the bigger risk are pretty rare. 

 

My my advice to the OP is get it looked at properly. 

[joepatr]

1 hour ago, Mark2 said:

Clearly this tree and your house have got on fine for a long time with no problem ! 

From the little we can see, it looks to have been well maintained! It also looks ‘of value ‘ in that area as there are few trees to be seen in photo.

How long have you lived there? And why do you want to remove it ?

conclusion—- strengthen foundations and regular maintence of tree !

I wanted to remove it purely to get light into the garden and also to protect the property.  Whilst there is no rush or risk right now apparent, I don’t want to threaten the property. 

 

I’m sure in the medium term it will also be more cost effective, rather than having to pay someone to come back every few years to maintain it. 

[Mark Bolam]

5 hours ago, benedmonds said:

Looks a lot more then 6m tall unless it has been topped just above the photo..?

Still not sure what a structural engineer will tell you...

 

 

Quite possible - it’s London!

 

A lot more about the structure of the house and the actual soil conditions than anyone else.

The house being the expensive part of the equation....

[Squaredy]

8 hours ago, Chris at eden said:

Why would you think that?  Subsidence is way more common than heave.  If the tree continues to grow then the subs risk will increase. If the frequency and length of droughts continue to increase then the risk of subs will increase. 

 

Then in again the house could have sufficient foundations. A lot of old houses have cellars. It’s difficult to say without the facts but the situation where heave is the bigger risk are pretty rare. 

 

My my advice to the OP is get it looked at properly. 

I meant the risk if the tree is removed.  Of course if the tree remains the risk is subsidence, but the OP was asking how to avoid heave if the tree is felled.

[Rough Hewn]

Get the house underpinned.
Keep the tree.
[emoji3][emoji106][emoji106][emoji106]

[Roz]

If you read Biddle heave is not as common as subsidence and in my experience from data supplied by insurance mitigation companies when you question the risk of heave they run around chasing their tails licking a finger and sticking it in the air to get an answer.

 

I am no expert but one factor that has to be considered  among others mentioned is the moisture content of the soil when the property was constructed?   I note  when it was built so while you wont have a definitive if for example built on already desiccated soil  this has continued to potentially dry out slowly over time with some seasonal re-wetting,   whereas a site which has been built on when the soil is at field capacity and has had the soil moisture gradient drastically modified by development etc may experience a more dramatic volume change? 

 

Doesn't answer the question to fell or not to fell but  another aspect to ponder.

[Khriss]

Insurance companies talk a lot of shite abt subsidence / heave. Got 4 cases ongoing myself and they basically want the tree OUT. Then they pay out. Actually had one insurance guy say to me ' oh NHBC guidelines 4.10 ? Nah mate that ain't relevant' k

[Mark2]

Haveing ‘slept on this one’

i reckon you’v already made three good decisions!

you decided to get unbiased advice from arbalk. 

You havent acted in hast to regret at leasure.

And you put your cards on the table and been honest about your motives. I like your style!

—- you’v made the right decision not rushing this, take a year or two,

there seem to be 3 parts to this problem. 1. The structural aspect. 2 your personal preference and 3,the legal and environmental impact.

Edited January 25, 2019 by Mark2

[Mark J]

If it was my tree, I'd be inclined to reduce it by maybe 15-20 percent and keep it about that size by pruning every few years.  My reasoning being: if it hasn't caused an episode of subsidence at its current size, a reduction may be significant enough to prevent it from doing so in the future.

That way, heave isn't very much of a consideration, the risk of subsidence is lowered, you get more light and the tree gets to stay.
It's not my tree though and I know nothing of the site or its history, but it may be an avenue worth exploring.

 

 

Edited January 25, 2019 by Mark J