Eucalyptus tree and foundations

[Ian Wroe]

Hi, looking for abit of advice if anyone is able to offer it.
I’m looking to build a 5x3m rear single storey extension to my 1930’s semi.
We have a eucalyptus tree in the garden which is big a rough guess at least 15m high. The new rear wall of the extension would be 7.5m from the tree. As part of the work I had planned to have the tree removed as I’m aware they can be abit of a problem and to have it pruned wasn’t much different to having it removed.
I have spoken with building control to try get a little more info regarding footing depths due to a few other trees we have, he has advised that although the tree will be cut down footing depths would have to be around 2.4m due to the eucalyptus, and advised speaking to a structural engineer or have mini piles. The garden is raised a meter up from the proposed extension so would be looking at around 3.4m deep from the base of the tree, but I don’t think this is taken into consideration? Any advice would be greatly appreciated as it’s looking very expensive to just get out out the ground, and whether it would be viable to get started. Many thanks

 

[DevilDamo]

As you may already be aware, the Eucalyptus is a high water demand tree and with a mature growth height of 18m. This coupled with a high, medium or low shrinkage soil will determine your foundation depths. With a distance of 7.5m to the tree, these depths range from 1.9m for low shrinkage, 2.25m for medium shrinkage and over 2.5m for high shrinkage, which requires an engineered solution as stated by BC. If you were within low-medium shrinkage, you could have had the option of stepping the foundations at various depths, but this does not appear to be an option for you.

 

[Ian Wroe]

Thanks for your reply, yes naively I assumed once the tree was removed this would resolve the need to go down so deep. I’m assuming this could get very expensive to just get out the ground?

 

[DevilDamo]

Removing a 14m high tree and its roots in their entirety?

It will not be cheap but engineered solutions are not as expensive as they used to be. I find a lot of contractors prefer to hand over the groundworks package to piling firms nowadays too. It’s just something you need to factor in.

 

[rssteve]

If you removed the tree and waited you could do the build at a later date. Basically the soil will gain moisture and expands upwards once the tree has stopped water intake. I'm not sure of times but I would of thought 2 winters worth of rain would allow enough time for the ground to change.

 

[Munroast]

I removed a Eucalyptus tree and its roots a few years ago, it wasn't a big tree, may be trunk was a foot in diameter, but its roots were just ridiculous I have never seen tree roots like it, took forever to dig out. they are well anchored in.

 

[JohnD]

might be too late now, but if you saw down a tree and (same day while the sap is still running) brush a couple of coats of undiluted Glyphosate concentrate on the cut surface, it will be drawn down to the roots and kill them. Apply more the following day (protect from rain). This prevents suckers and regrowth.

If you see any green shots later, cut them off and dab on more concentrate or, if flexible, turn them upside down and submerge them in a jar of it for a few minutes. Also works on ivy.

Yes, it really does work, and does not poison the soil or adjacent plants.

 

[^woody^]

might be too late now, but if you saw down a tree and (same day while the sap is still running) brush a couple of coats of undiluted Glyphosate concentrate on the cut surface, it will be drawn down to the roots and kill them. Apply more the following day (protect from rain). This prevents suckers and regrowth.

If you see any green shots later, cut them off and dab on more concentrate or, if flexible, turn them upside down and submerge them in a jar of it for a few minutes. Also works on ivy.

Yes, it really does work, and does not poison the soil or adjacent plants.

But if you saw down a tree to ground level, don't the roots die anyway?

 

[Munroast]

But if you saw down a tree to ground level, don't the roots die anyway?

99% of the time - BUT - if it is really really important that they don't spring back into life then they probably will.

 

[JohnD]

But if you saw down a tree to ground level, don't the roots die anyway?

No.

 

[mikeey84]

No.

Well that depends on the tree.

Some do die when you cut them down to ground level, others don't.

 

[Londoner2]

A neighbour removed a medium conifer about 10m away from house back in 2014, this resulted in my patio/outbuilding movement due to roots shrinkage.

 

[frutbunn]

A neighbour removed a medium conifer about 10m away from house back in 2014, this resulted in my patio/outbuilding movement due to roots shrinkage.

More likely to be caused by clay heave.