Even small churches need a place to worship and carry out the work of formation and mission that makes them into full (if not filled) places. The smallest churches tend to fall into one of two solutions:
- Rented or borrowed space
- An owned space, often built when there were many more members
Given my choice, I'd rather meet in a conference room for two hours a week than be part of a little crew rolling around an enormous edifice like bbs in a box. For one, the former is easier to maintain and small congregations are already inconvenienced for participants. The second reason: a near-empty church signals an unhealthy congregation, even if it plugs along satisfying its own members. (Not necessarily an unrelated phenomena, but for consideration another time.)
But how much space?
Be sure to grab the Air Force's Religious Facilities Design Guide from Archives.org (the original Air Force site is down) for a steely-eyed idea. (Does anyone else have a suggestion?)
Space too big? Other than decamping within the building to a parlor or workroom -- unpopular ideas I'd imagine -- I've seen big buildings/small congregations partition off the nave with screens and plants to keep the worshipers within hymn-singing distance of one another. But that won't save you a cent on heating bills.