A counter for houses or buildings meaning one house/building (used for standalone houses, shops, etc.).
その通りには空き家が一軒ある。
There is one vacant house on that street.
私の実家は一軒家で庭が広い。
My parents' home is a detached house and has a large garden.
新しい店を一軒開く計画を立てている。
I'm planning to open a new shop.