There are 11 million empty houses all over European Union. 3.4 million of them are located in Spain, 2 million in France, 2 million in Italy, 1.8 million in Germany, and 0.7 million in the UK, according to ee24.сom citing kyero.com.
There are also many empty houses in countries with relatively cheap property, such as Greece and Portugal. These buildings were built mostly before the crisis, but nobody ever lived there. A lot of these houses were bought by investors who are waiting for increase in prices.
It's estimated that there are 4.1 million homeless people in the EU. But if all investors put their European property for sale, this would reflect negatively on the European economy.