When the iD editor raises the "Building crosses Foot Path" or "Building crosses Highway" issues, the first two suggestions are "Tag this as higher" and "Tag this as lower". Unfortunately, these options used in isolation are almost always wrong. Not only do they not fix the problem, but they also hide it from QA tools which would help other users to really fix the problem. This isn't your fault, it's one of the many design flaws in the iD editor where suggested improvements actually degrade the map.

This particular problem can be fixed by realigning the building, using the OSMUK Cadastral Parcels overlay.

In other cases, where there is a driveway or passageway through a building, the highway can be split where it joins the building and tunnel=building_passage added to the section in the building. It rarely needs a layer tag.

I've realigned the terrace on Railway Street in https://www.openstreetmap.org/changeset/162493336