I have an old home (new to us) on a typical suburban lot with a pretty narrow driveway that cannot accommodate two modern vehicles side by side. After doing the daily vehicle shuffle with my wife for a while now, I'm contemplating expanding the driveway footprint. However, my neighbor has a mature sweetgum tree about 20' away that has sent pretty substantial roots right where I would want to pour the new concrete. The new pad would be 3-5' inside my property line, but the roots will be in the way regardless of the offset. I'd estimate the main root in question is ~5" in diameter, so I'm guessing cutting it would potentially cause damage to the tree. I haven't yet consulted an arborist, and there may be more I can't see underground. Unfortunately, the HOA rules explicitly prohibit a less permanent/more porous option like gravel.

Curious on the board's opinion on how to approach this with my neighbor, if at all. Am I overthinking/overstating how much damage it will do to the tree, or should I seek to get the project blessed by my neighbor before moving forward? I don't want to be a crappy neighbor and damage his tree (spiky seed pods notwithstanding), but at the same time, I don't know how much free "right of way" is appropriate to give a neighbor's tree when it's impacting the usage of my property.

If you and the neighbor have a good relationship, or you want one. I would ask an arborist opinion on expected damage to the tree should you remove the roots to widen your driveway. See if you could get it in writing to show your neighbor you went through the effort to try to minimize damage to his tree.

If you are going to sever less than 1/3 of the entire root system, then don't worry about it.
The tree can handle it, just as it could pruning branches.
How much of the expanded driveway is in the critical root zone?

Talk to an arborist.

Root pruning can be done. A&M has done this plenty. There is a process to make it easier on the tree.

It may involve pruning limbs to in order to take some load off of the tree and it may need to be done in stages if it is severe enough. May include adding fertilizer, etc. to help compensate for a while until the tree can adjust.

An arborist should be able to walk you thru the correct steps.

this. you can cut limbs that hang over your fence. you can cut roots that run under it.

Jason_Roofer said:

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Nothing to ask about. Dig out your drive, cut out everything that's in the way. We have cut out 6 and 8" roots from liveoaks that were damaging old structures. The trees don't seem to care. Your neighbor probably doesn't even know they are there. Cut them. Do what you need to do.

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I agree with this. I added a carport to my home, and there was a tree close by that I didn't want to cut down. We took a good portion of roots and a large branch. That was three years ago, and the tree is just fine.

Neil Sperry just addressed this as maybe OK on his weekend radio show within weeks of this writing.
I'll bet sending photos to him for an opinion might be the icebreaker a neighbor might welcome if concerned about "his roots" & tree health.

You also have respected opinions found here as well to take to neighbor.

Failing that, I'm wonder if you can find a draftsman or better to draw a driveway expansion on the other side, away from such roots ... that are adding to costs.