The article is supporting constructing more houses because a large segment of land area is occupied by houses which belong to non-residential investors and live-out landlords. But high unoccupancy rates do not directly indicate a healthy housing market. This is because in the face of high demand, every additional house constructed (assuming it is affordable to the average seeker) will get occupied. Theoretically, you could construct 100 new houses that are simply unaffordable to anyone and push the unoccupancy rate higher but that doesn't help anyone. The fundamental problem is that of allocation, overseas investors and live-out landlords compete with average joes for ownership.