On 23/07/2016 18:20, DerbyBorn wrote:
being a
kitchen and a separate flat upstairs. I guess this would apply to the
ceiling as well if/when I do it?

Tim


....or is it one of those jobs that a professional wouuld simply eat and
have it done perfectly in a few hours whilst you are struggling with broken
sheets?


No. Why would the sheets become broken, when new plasterboard has some
flexibility ?.

If the existing timer uprights are way off plumb then add another set of
correctly spaced horizonal noggins cut to fit the gaps
between the verticals but aligned horizintally to give a flat wall.