Related Clues:
- Enlarge a house
- Not standard
- Computer peripheral, e.g.
- Arm or leg, e.g.
- Supplemental component
- Home builder's afterthought
- Expansion
- Garage, perhaps
- Building wing, e.g.
- Extra, and this puzzle's title
- Include as a bonus
- Build an annex
- Enlargement
- Optional item as supplement or increment
- Might a priest finish one of 6 down for an attachment