Can you build over or under an easement?

In brief – "Substantial" or "material" interference with easement is key test

Normally an easement will not prevent you from building over or under it. For example, if there is an access way through your property, you probably will be able to put a sewer under it or a structure over it.

But whether or not you actually can build over it will generally depend on whether your proposal causes substantial interference to someone else's rights.

What if there is an easement over your property?

An easement gives someone the right to use a section of land for a specific purpose even though they are not the owner of that land. Typically this could be a access way or an easement for drainage.