I did the maths for this a while back, we already have way more rooms per 1000 people than the euro average, they just have more properties per 1000. I guess this comes from our historically larger families.
The numbers:
Ireland has the 2nd largest houses on average, with 5.3 rooms per dewelling. The euro average is 4.32 rooms per dwelling.
So if we have 410 dewllings per 1,000 people, at 5.3 rooms per dwelling we have, 410*5.3= 2173 rooms per 1,000 people
European average is:465 * 4.32 = 2008.8 rooms per 1,000 people,
So we already have way more rooms than the euro average!
On average European dwellings are larger than in Ireland, 90 sqm vs 88.3 sqm. but I dont' think building more tiny dwellings is going to help that figure much.
source of dwelling size data:
http://www.finfacts.com/irelandbusinessnews/publish/article_10005314.shtml