Q. If a Muslim has money set aside to purchase a house, is it necessary to pay Zakat on that money?
A. Zakaat is compulsory upon a person when he has a savings over the Nisaab and one year has passed over this saving.
The fact that the person still has the money with him means that he is in the possession of a nisaab/savings and must pay Zakaah on the money.
So, the answer to your question is that a Muslim will pay Zakaah on the monies which he has set aside to purchase a house when the year has come to an end and he has not yet used the monies.
And Allah knows best.
Mufti Waseem Khan