UKTC Archive

Re: Subsidence where foundations less than 300mm deep

Subject: Re: Subsidence where foundations less than 300mm deep
From: Bill Anderson
Date: Sep 08 2020 08:46:45
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






--
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




-- 
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