UKTC Archive

Re: Subsidence where foundations less than 300mm deep

Subject: Re: Subsidence where foundations less than 300mm deep
From: Jerry Ross
Date: Sep 08 2020 08:13:35
...in other words, it's a building design problem of structures that aren't designed to withstand the naturally occurring stresses that they're likely to be subjected to out in the real world. When houses fail to keep out the rain or have roofs that don't stay on, these are regarded as problems of poor design and/or build. But an unholy alliance between insurers, volume house builders and a flourishingly profitable subsidence claims industry conspire to attribute the cause of buildings developing symptoms of subsidence due to differential soil drying, solely to the malign influence of trees. What's more, in the majority of cases the damage that occurs is rather minor, often confined to non-structural cracks and the like, matters that could be dealt with by other, non-destructive means. The fact is that because of the terror of subsidence that has been instilled in property owners by the aforementioned conspirators, the most significant damage caused by these claims is to the equity those properties represent, a subs claim (even one that's been resolved) being likely to knock many thousands of pounds off the value of a property.

There.  Got that off my chest.



On 08/09/2020 08:40, Alastair Durkin wrote:
Hi Wayne

Essentially in certain parts of the UK (particularly London) there are large 
amounts of clay present at, and below, foundation depth (clay shrinks 
significantly when water is sucked out of it, unlike sand - for example). 
Buildings that were built pre Building Regulations with shallow foundations 
can suffer differential movement due to the drying of soils underneath and 
around these foundations, particularly when trees are growing nearby. This 
can also happen to modern buildings where trees are planted within 
influencing distance, and is a particular problem when extensions are built 
with an insufficiently deep foundations, as they move differently to the 
parent building (assuming it has deeper foundations). There are lots of other 
elements to take into account, but I think that is basically it.

Piled foundations can be the answer to all this, but they are expensive.

Alastair


-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info <uktc-request@xxxxxx.tree-care.info> 
On Behalf Of Wayne Tyson
Sent: 07 September 2020 21:57
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Subject: Re: Subsidence where foundations less than 300mm deep

Pardon the density of my gray matter, but I continue to fail to see why trees are 
blamed for subsidence. Perhaps I haven't been paying attention, but is this cited 
anywhere in the US? Are there scientific studies demonstrating the fact? I understand 
the "theory," but question the conclusion.

The engineers I know would use pilings instead of foundations. Then there's 
the famous Frank-Lloyd Wright-designed hotel in Japan.

Would anyone care to lead me out of the darkness?

Wayne

On Mon, Sep 7, 2020 at 5:15 AM Jon Heuch <jh@xxxxxxxx.co.uk> wrote:

Trevor



There is nothing magic/noteworthy about 300 mm deep foundations.



What I expect they are trying to say is that seasonal movement in a
property should be less the deeper the foundations. With shallow
foundations some seasonal movement can be expected & identifying the
cause of that movement with shallow foundations can sometimes be
problematic.



a.      Would the same or similar movement have occurred without the trees?
b.      Will removal of the trees solve the problem i.e. reduce the
seasonal
movement to within acceptable limits?



"no other cause produces a similar pattern"....well I wouldn't state
this definitely related to a 300 mm foundation. It depends what the
structure is so a light weight structure such as a garage might move
seasonally on a 500mm foundation without any trees..whether that is a
problem or not depends upon the structure and whether it can put up
with the differential movement.




Jon






--
The UK Tree Care mailing list
To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info

The UKTC forum is supported by Bosky Trees arboricultural consultancy
and Stockholm Tree Pits https://www.stockholmtreepits.co.uk







--
The UK Tree Care mailing list
To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info

The UKTC forum is supported by Bosky Trees arboricultural consultancy and
Stockholm Tree Pits
https://www.stockholmtreepits.co.uk