The short answer.  As far as possible.

Plants are constantly growing taller and spreading wider.

When planting small to medium shrubs my goal is 1-2 feet of air between the edge of a shrub and the home.  Not just when I plant.  For the life of the landscape.

You can prune the back of a shrub, where no one sees, as often as needed to keep the gap.

If there isn’t a gap you’re in trouble.

Medium shrubs like Rhododendrons, Azaleas, Spirea, Holly and Boxwood go  2.5-3′ from the side of the house.

I can easily walk behind the shrubs after planting.

Large shrubs and small trees like Viburnum, Dogwood and Stewartia go a minimum of 6′ from the edge of the house and preferably 8′.

When in doubt plant farther from the house.  You’ll never regret it.