Is it your sidewalk or the city's sidewalk? First review the laws; you may not have the options you have described.

If it really is your sidewalk and your property, is it possible to detour around the offending roots with a gentle curve? Otherwise, you may have to remove the roots and re-pour the concrete. Any other material with the roots intact will not be a walkway, but a hazard.

If this isn't a public sidewalk at the street, Kim's suggestion to reroute the walk further away from the tree trunks is probably the best approach. If the new walk is also going to be concrete, you might want to include a root barrier with a biocide impregnated on one side to keep new roots from doing the same thing.

If this walk is not a public sidewalk, and your situation allows, using a raised boardwalk to span the offending roots with sleepers set over concrete piers may be a better way to cross this area with least disturbance of existing tree roots.

Some pictures of the spot and more information would be useful to give better advice.

You might research a non permeable product called Terra Pave to see if it is a good fit with your climate and site specific situation.

Terra pave was recently installed in a very upscale old established neighborhood as a pedestrian and bike path . This neighborhood had its streets lined with old established heritage trees that had tons of tree roots lifting the sidewalks.

The city removed the damaged concrete paths and replaced the path with decomposed granite.
The upscale ( multi gazillion dollar homes ) neighbors complained that the decompose granite was 'dirty' and tracked onto their driveways.
So they removed the decomposed granite and installed Terra Pave.
Terra Pave looks like a cross between asphalt and decomposed granite.
It is non porous and extremely stable.
It cannot be installed during the rainy season due to the natural stabilizer ( I think it is pine pitch ).
Locally in Northern California a company called Wheeler Zameroni offers it.

You might check out the spec's and see if it is a good fit for your installation.

Thank you for all the messages.

Yes, the sidewalk is privately owned and maintained by the landlord.

I will be looking at all these options, though we do need to go over the roots at some points, as there is not enough room for a small pathway around them.

Will the tree not be damaged if we cut through its roots? It is old and big, but still...

I found Terrapave on the web and I am also looking at decomposed granite, but that does not sound like the best choice.

Many thanks again.

If those big roots are lifting the sidewalk next to the house, they are on their way to the house. Most trees can sustain damage to the odd root but some don't take well to it at all and damage to several roots is likely not a good idea - especially for a large tree near a house, since roots function in part to keep trees upright. Learning what kind of tree it is will help you determine not only how it is likely to respond to root cutting but also what its roots (and the rest of it) are likely to do in the future.

One thing I have done around tree roots is to use paving stones, laying them around and between the tree roots. But this has only been for a back pathway to the alley; for a front sidewalk used by guests or the mail carrier, this is not good enough.

Bottom line is that if a tree is causing trouble around structures, you want to think about the long term viability of this tree in this location before doing contortions to adapt to the tree. You might put thousands into a new sidewalk only to find that the tree is removed within five years for its other incursions as it grows... canopy, other root problems, etc.

KarinL