Giant tree roots above ground

Newbie question. My parents' house's backyard has 2 very large trees with thick roots that stick above ground 2-3 inches , and radiate from the base of the tree about 20-30 feet. All the grass underneath the trees are gone because of the canopy and years of dead leaves. Took 26 55 gallon garbage bags to dispose of the leaves and small branches Left behind lots of mulch, though.
Do I get lots of topsoil and cover up the roots? How deep under the topsoil should the roots be? This is flat ground. For one tree, it is at the base of a hill.
Also, can anyone recommend grass seed which grows with very little sunlight?
THanks
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First, explain where you live and what kind of trees they are. And, it might be good (and free) to call your states cooperative extension service and ask about those trees.
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This last bit is good advice. Depending upon the type of tree (although it's generally inadvisable for most) covering those roots with soil could damage and/or possibly even kill the tree. As for the type of grass seed that grows in little sunlight, that can also be answered by your cooperative extension since they're intimately familiar with your area, and it could also be affected by the type of tree. There are some varieties that sap so many nutrients from the ground as to make it impossible to grow turf grass beneath them.
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And, some trees will send up a network of fine roots into the soil you pile around them, which ends up defeating your purpose, since not much will grow in that medium. I think the OP would be better off looking into ground covers that'll put up with funky soil and not-so-much water. Vinca is one. Not exciting, but neither is throwing grass seed at a spot where it won't grow.
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