Obviously the higher the ceiling height, the better, but it's not uncommon to end up with a ceiling height less than the 2.3m your architect is suggesting. Unless the Building Regs have recently changed, there is no legal minimum ceiling height. However there is still a practical minimum height you should work to in loft conversions of at least 2.1m throughout (standard ceiling height elsewhere should be at least 2.4m). Ideally in rooms with sloping ceilings, at least 50% of the floor area should have a floor to ceiling height of at least 2.1m. I recently saw a rear dormer conversion where the ceiling height was only 2.05m because of existing parameters. I'm 6 foot plus, yes it felt lower than normal, but most loft conversions tend to have a 'quirky' feel to them anyway. If you can, you should try and view a loft conversion with a ceiling height lower than your architect is suggesting. rahrahrah, I get where you're coming from, but unless you can find a builder that will guarantee at their expense, any remedial works needed to conform to Permitted Development or Planning Permission should the planners find out the builder has been too 'liberal' in their interpretation, then there is a large financial risk for the householder if they get 'found out'. Trust me, some planning officers can be real sticklers for regulations. By law an architect has to carry professional indemnity insurance, so therefore they can at least be sued for giving bad professional advice. With a builder you'll be lucky to get more than a shrug of the shoulders out of them if things go wrong...