"Stan The Man" wrote in message
...
I'm planning to remove a 35m-long double-planted row of very
well-established leylandii (approx 30 years old) from my front boundary
which is 4m from the front of the detached house (purchased last year),
part of which was built 100 years ago with a sizeable extension added
15 years ago.

This dense hedge was 10m tall until I cut the top off at the end of
last year in preparation for the coup de grace. It is now 4m tall. Some
of the trunks are 300mm diameter and I'm concerned about their root
systems. How far are they likely to have spread in poor-draining, clay
soil?

And what, if any, could be the risk to the foundations of the house?
Removing so many at once will presumably have a significant impact upon
the soil structure and drainage. There used to be a drainage ditch
along the front of them but this was filled in some years ago and
surface water collects rather easily in heavy rain. Without the trees
to consume a lot of it, I'm worried about drainage. Should I put in a
soakaway? TIA.

Simon

The root spread on it's own is not the real problem. Nor is the fact that
some of the trunks are 300mm in diameter, (which in this double row case,
may mean double the density of such trunks)
The real issue is the clay soil and foliage cover of the trees and the fact
that 4m is not really all that far away in such circumstances.
Not only do they soak up the surface water, but also play a part in
controlling the water table.
When digging a large hole to assess the foundations of a building, a certain
volume of water will appear in the hole having being released from under the
foundations as a consequence of digging the hole.
Reducing the trees, as you have done will help to minimise the effect, but
I'd be inclined to reduce them even further this year (to 2m) and then next
year remove them entirely.
However, you would be best advised to get direct, on site professional
advice
As for creating a surface drain, structurally, that'll probably be more a
matter of convenience for you in terms of your ability to use and enjoy the
property.... unless off course your talking about volumes of surface water
capable of washing the building away (-;

Patrick