tree roots & buildings

[simonm]

Could damage occur to a building if tree roots were growing underneath and the tree was removed??? we have removed Lombardy Pops before because they were sucking moisture out of the clay causing it to contract which left a void under the building which led to cracks appearing along a wall. I have never known of damage further down the line due to removal though .

I suppose if they were fairly substantial they would leave a void as they broke down??? creating unsupported footings? would not apply to something built on a raft though ???

[Gary Prentice]

depends on which was there first

[Kveldssanger]

depends on which was there first

 

Exactly this. If a structure is built upon an existing root crown area, and the root crown area rots away as the tree is felled / dies, then you may see some shifting as the soil is displaced and fills the voids. On the flip side, if the tree is planted after a structure is built and causes soil to shift in a heaving manner, the structure can only revert back to its original level as it were before the roots became an issue.

[Shane]

How severe is the root-void issue in reality?

 

Wouldnt the roots decompose slowly but gradually morph into a compost rather than leave an empty space?

 

I can see that the resulting 'mush' would be less supportive but have often wondered what really happens. We all know that surveyors tend to err on the side of caution and that insurance companies are always looking for a get-out.

 

No doubt some of the academics on here can enlighten us more than I ever could.

[Gary Prentice]

I think the OP is a little confused as to the reason for removal. Moisture loss causing structural damage (which should be seasonal and supported by level monitoring) suggests shrinkable clays, so the issue is volumetric changes ie heave/subsidence

[Kveldssanger]

I'd also take a guess and suggest most lombardy pops are planted after development, given they don't last too long. Any lombardy pops would likely be cleared before building, as well, if some did exist on a building site.

[Kveldssanger]

OP - my comment on roots also applies to subsidence and heave.

 

If a structure is built on shrinkable soil, a tree is then planted after construction and the site begins to subside, upon removal of the cause the ground can only re-hydrate itself back to its size as it was when the structure was built (assuming there was no desiccation at the time).

 

Alternatively, if a structure is built upon an already desiccated soil with some trees retained during development, their removal might cause heaving issues if the soil re-hydrates to a point where such re-accumulation of moisture expands the soil to levels the structure has not previously been exposed to. Thus, heaving cracks.

[Tom D]

The issue with shrinkable clay is that the ground swells once the trees have gone, the rotting of the roots is not the issue. When trees grow on shrinkable clay they suck up a lot of moisture which shrinks the clay. when the trees are gone the clay re-hydrates and expands.