There are a finite amount of houses in the world, and a greater number of people who want a house.
Scarcity is the economic concept that there is insufficient productive resources to meet all human wants and needs. I think we agree on that. I think your contention here is the "want" rather than the "need".
Of course there is a finite number of houses in the world. There is a finite amount of eveything. However, according to the Cenus Bureau, as of Q4 of 2013, the rental unit vacancy rate was 8.2% and more than 300,000 homes are foreclosed and unoccupied according to RealtyTrac. That's 8.2% of rental units that would be making more money than they are now if the rent on them was $10/month and 300,000 homes that are wasted livable space. There is no real shortage of housing in terms of need. People might want bigger and better, but there is no excuse for there to not exist housing that eveyone can afford.
There is no scarcity of food. We throw tons of it away constantly. The only thing holding us back from supplying as much food (with current production levels) as the world could ever need is a societal problem where we cannot bring ourselves to help eachother out. Current food needs are fully funded (by the people who are throwing away food). The only expense that should exist in providing food to low income families is logistics.
The only thing stopping us from solving the human population's basic needs is greed. Our society has been taking great pride in this greed for the last several hundred years and I don't expect the problem to be solved within my lifetime. But humanity should at least admit its problem and lower its head in shame rather than taking pride in climbing on top of other people.