I use the NHBC span table.
http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2010/Part6/section4/appendix.htm
A 170 x 47 gives a 3.7m span - going to 8 x 2 wouldnt be a bad ides.
http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2010/Part6/section4/appendix.htm
A 170 x 47 gives a 3.7m span - going to 8 x 2 wouldnt be a bad ides.