An annexe is the most useful aspect of a property a homeowner can have. But I use the term 'annexe' in the loosest sense. The more separate and self-contained the better, but as long as it's space that's self-contained in terms of bedroom/bathroom/very basic kitchen that might just include a kettle and microwave, it meets the criteria.
An annexe provides a useful way of living and infinite flexibility. Guests can be less ever-present, they're a halfway house for children who haven't quite flown the nest, a wonderful place for family to stay for extended visits, great for nanny or au pair, or a permanent home for elderly parents or grandparents who can no longer live alone.
For the times in life that none of the above apply, the homeowner has the luxury of finding their own use for the space – either as a place of work or play, or to generate some cash on a regular or occasional basis. It's win-win.
While an annexe may just be a separate area of the house, the best are independent in layout with their own access, outside space and utilities. Homeowners who have too much space within the main property would do well to think of ways of carving the space up and adapting it to create an annexe. If the main house doesn't have any spare space, but there's outside space available, think about creating completely separate secondary accommodation. There are a host of options ranging from a proper new build, to converting an existing building, to a shepherd's hut, to a caravan.
Bear in mind that planning permission for an annexe is generally granted on the basis that the property can't be sold separately. There may be other restrictions attached regarding use, especially relating to renting out – check these carefully before you invest.
Be careful of making decisions about secondary accommodation that are based entirely on income rather than utility. Do realistic sums about costs and likely occupancy / rates, and work out how long it will take to pay off the investment.
If you're buying a new property, one with an annexe really is an excellent proposition for almost every stage of life, and allows for so much flexibility. Even if you hadn't thought you needed one, think about the benefits and how it may make the property viable for a much longer life, negating the need to move, and saving huge sums of money in moving costs.
