The biggest trends in new homes right now are built-in solar panels and separate apartments for aging relatives.

It typically costs $10,000 to $20,000 to retrofit an existing house with solar panels, but builders are increasingly putting them into new homes. Buyers can then choose to purchase the system or lease electricity from the builder.

Buying the system costs more upfront, and the full cost might not be reflected in a mortgage appraisal. But doing so can save money in the long run, especially since homeowners who generate more power than they need can often sell it to an electric company for a credit.

Leasing is cheaper initially, and can still result in significant savings over buying power at full price from a utility.

As for in-law apartments, a recent survey of homeowners by a major builder found that 32% expected to have an aging relative living with them at some point in the future.

Builders are responding by creating homes with one-bedroom apartments with separate entrances, and in some cases small cottages separate from the main house. These often sell at a very significant premium.

Houses with separate units are still restricted by zoning rules in many areas, but lobbying groups such as AARP have been working hard to change these laws.