Zakat is due on income/proceeds from the sale of the house if the sale is done on the basis of profit /business. Having mentioned that, if the sale is done after a year passed ever since the intention to sell the house on the basis of profit/business is made, Zakat on Business is based on 2.5% of the income from sale if it reaches the nisab. If the house is for normal residence and not business, income/proceeds from the sale is not due for Zakat. Nevertheless, if the income/proceeds is kept for a year (haul) and reaches nisab together with other savings, Zakat is due i.e. Zakat on Savings.