The housing market is heating back up. But only a small percentage of new homes are fully-built.

• New-home sales jumped 8% in December as mortgage rates fell.
• But most of the new homes aren't yet complete, with only 17.9% ready for move-in.
• Builders are racing to meet supply needs as existing homeowners stay out of the market.

New-home sales rebounded in December, rising 8% as homebuyers rushed to take advantage of falling mortgage rates, US Census Bureau data shows.

But while consumers appear eager to re-engage with the housing market, new purchases don't mean an immediate move-in for some.