...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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