How to identify tree roots that have lifted concrete slab?

[BBY]

Some large plant has lifted my Garden shed concrete slab on one side. The slab is very close to my fence on the other side of which is my neighbour's 20 year old Giant Bird of Paradise, some palm trees and a very small section of thin bamboo, all in very close proximity to the fence. I suspect that the main culprit is the Giant Bird of Paradise or the Palm trees. Action taken to date includes cutting down the tall trunks of the Bird of Paradise (neighbour does not wish to kill it and it has since re-grown as he does not believe its roots are the cause). Have also dug up the soil between the plant and the fence (close to the Bird of Paradise) but could not locate any large roots that could be causing the problem. I suspect that we did not dig deep enough (about 40 cms) to get to the roots! Any ideas? I am thinking of getting an arborist to prepare a report which identifies the cause. I would appreciate any ideas and similar experiences other community members have had.

[MitchellMc]

Welcome to the Bunnings Workshop community @BBY. It's wonderful to have you join us, and many thanks for your question about concrete slabs.

I’d recommend continuing to dig a trench along the length of the fence, but dig deeper than 40 cm — ideally, to a depth of 60 cm to 1 meter. This will help ensure you reach any larger, more invasive roots that might be spreading under the concrete slab. It’s also possible that the roots are tangled and harder to spot, so a larger excavation may reveal them. As for the arborist, it could be helpful for them to see this work already done, as it would give them a better idea of the root system's extent and whether it’s likely to be the cause. Without seeing visible roots under the slab, it might be difficult for them to confirm the exact culprit, but the trenching will provide solid evidence to support their investigation. Additionally, if the root system is extensive, the arborist may recommend cutting back or even removing certain plants to prevent further damage. It’s definitely worth continuing the trenching to ensure all potential roots are addressed before moving forward with any more drastic measures.

Please let me know if you have any questions.

Mitchell