The full paper is available on www.esri.ie but I will give just a short summary as with most academic economic papers it has a good amount of econmetrics which is very heavy going stuff, although he seems to have conciously kept it to a minimum and to have written the remainder of the paper with a view of making it readable to people other than economists.
The headline from the paper is that from his analysis of housing collapses across the OECD since 1970 is that housing booms give up upto 70% of there gains. On this basis he reckons that the Irish housing market could fall 40-60% over the next 8-9 years. However, what is not highlighted in the reporting of the paper is that he actually reckons the 40-60% fall is an fact a conservative estimate and that it could be even higher!!!
Note also that his figures are based on real (inflation adjusted) figures. So for comparative purposes if house values fell 5% nominally this year then combined with a 5% inflation rate then that would be the first 10% of the 40-60% fall that he is predicting. A lot of people I think will eronously assume that he means 40-60% of the nominal value rather than the real (inflation adjusted) value. This should really have been made clear in the reporting but never was.