Vaastu is all about magnetic energy flow. Many people doesn't understand this concept. We all studied this in 7 or 8th grade.
So why north / East facing housing is good. means.
Energy flows from North to South and we all learnt this in 7 or 8 th grade science. So when the North is open the energy flows inside your house and you should block your South-west.
So ideal is House faces North is 1st degree.
North East should be open
South West should be closed.
Even if you buy house with perfect vaastu if you have window on South west and if it kept open you may face financial, Person who lives there faces un-stable issues. When someone is not balanced then you know what happens in the family.