UKTC Archive

RE: Subsidence where foundations less than 300mm deep

Subject: RE: Subsidence where foundations less than 300mm deep
From: Liam McKarry
Date: Sep 08 2020 15:02:14
The question is whether the damage would have occurred without the tree roots 
being present beneath foundations and following that can a link be proven 
between the tree and the damage through soil testing, crack width or level 
monitoring and root id.

Whether we like it or not inadequate foundations is rarely a good defence if 
the property is on a clay soil with a cyclical pattern of movement

Regards

Liam McKarry
Arboricultural Officer (Planning)
Colchester Borough Council
Rowan House
33 Sheepen Road
Colchester
CO3 3WG
01206 XXXXXX



-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info <uktc-request@xxxxxx.tree-care.info> 
On Behalf Of Bill Anderson
Sent: 08 September 2020 09:46
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Subject: Re: Subsidence where foundations less than 300mm deep

This message originated Externally. Do not click links or open attachments 
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Not to mention all the other things that might lead to soil moisture not 
being replenished; things such as building a house and shoving the rain that 
falls on the roof into the sewerage system rather than back into the soil, 
building a road that diverts its rainfall into the drainage system rather 
than into the soil, compacting the soil by mowing the grass so the rain runs 
off rather than soaking in, creating "pans" by ploughing, and I'm sure 
there's other stuff. But yes I've no idea how trees came to be seen as the 
major problem.

On Tue, 8 Sep 2020 at 09:13, Jerry Ross <trees@xxxxxxxxxx.co.uk> wrote:

...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






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