Will a root lifting a slab decay and drop the slab?

What kind of tree root?

There are many kinds of tree roots that after being severed will keep growing, and form new trees!

esp; popcorn trees ( Sapium sebiferum) and empress tree (Paulownia tomentosa)...privet (Ligustrum sp.) Also... Mulberries and figs!

Root cuttings is a common method of propagation...

Add me to the nay sayers... once pushed up, the cement is likely to stay up. Even with the decomposition of the tree root.

Soil is full of holes... They have to pack the soil before adding hardscape, and even so... it doesn't stay compressed.

Consider frost heave...

In areas with freezing winters, the moisture in the soil freezes and expands, forcing the pavement to buckle. Those roads don't settle afterward, and must be re-compacted, and patched.

Probably not. Yes the root will die, decompose, and leave a hollow spot under the slab, but there will be dirt that filled in the emptied space as the root was lifting the slab holding it up. Think of a board balanced on a can, there's a lot of empty space around the can under the board and above the ground, and over time that fills with dirt washed in by rain, carried by animals, etc. When the root rots away, that dirt will still be there holding it up. However, with an empty hole underneath it, the slab might break if it was somewhat thin and the root was quite large.

So I guess it depends on how solid the dirt is. If it flows easily, it might just shift into the empty space left by the root and allow the slab to lower somewhat (in which case you'd be right). If it's quite solid, the slab wouldn't lower much at all, though it could break where the empty hole is.

I can't think of any trees whose roots would keep growing after being disconnected from the tree, so I'm pretty sure that first person is just plain wrong.

This is based on personal experience. I owned a rental property. The driveway was heaved and broken in several areas from pine tree roots. I had the roots cut back and the driveway torn out and re-poured, removing all of the severed roots. Six month later the drive was showing signs of heaving from new roots growing off of the severed roots. I had the tree removed. When we purchased our home in the late 80's there were pine trees planted every 10' on both side of the lot. We had them removed and the stumps ground. Over the years we have installed flower beds, vegetable gardens and my husband built a large shop. During the last 10 years we have had holes appear in the beds and gardens where the stump finally rotted out. That was not a big problem. The problem is where the slab of the shop is over the old stumps. We have had to fill stump holes with concrete to avoid damage to the slab. This is on going because the tap root is also rotting out so the concrete fill sinks every year and more has to be added. I live in south Louisiana so there is no issue of soil heaving from freeze. That is another issue.

Good luck

I assume you want to get rid of the roots under the slab and keep the tree if so just cut back the invasive roots some place between the tree and the slab. They may grow out again but it will take years before the are big enough to be a problem again. If you don't find big roots(as big as your arm) going under the slab the cracks may be caused by general earth movement or settling which you can't do anything about.

I think you are correct, but your friend who says the slab will just stay lifted has a point. While the portion of the root no longer attached to the tree will rot, the length of time this will take depends on your climate, the species of tree, and other organisms such as termites. Smaller roots will send out new roots at the point where the root is cut, and this won't help your situation. However, cutting the root will prevent further lifting of the slab, so the problem shouldn't get worse.

http://www.gfc.state.ga.us/community-forests/ask-t...