| +/- landuse=residential
Predominantly houses or apartment buildings.
An area of land dedicated to, or having predominantly residential houses or apartment buildings.
If there is a small (one company/property) area of commercial (or similar) landuse within an otherwise residential area, you can still use landuse=residential for the outline of the whole larger area. You could later draw a separate area tagged with landuse=commercial for that commercial establishment (but in general a residential area does not change its character just because of a single business. This depends on the kind and size of the differing usage).
The landuse tag is mostly used for larger areas and not at parcel granularity; as described above, a single shop in a residential area does not warrant an extra "commercial" landuse.
Of course, if the change in landuse is relevant, then it makes sense to map it. Relevance can either come from size - if there is a whole shopping mall in a residential area, one would probably map this separately - but even something small can be relevant. This is the mapper's decision. If you want to make a hole for another landuse inside a residential area, you can use a multipolygon relation for that.
Separation from roads
It is perfectly ok for a (small) road to lead through a residential area. Nevertheless some mappers split residential areas into blocks that do not contain any streets; others restrict such splitting to major thoroughfares, and still others draw one big residential area around a whole town.
If you choose to let a landuse area end at a road, you have a choice of either re-using the nodes of the way representing the road, or drawing the boundary using new nodes next to the road. Both methods have their advantages and disadvantages, and neither is wrong.
If you had access to land parcel data, you'd probably draw the ways with landuse=residential along the parcel edges, which are (mostly anyway) some distance away from the road centerline, i.e. behind the sidewalk. Draw accordingly or discuss at Key:landuse discussion page.
Related terms: <residential landuse>