PVC gutters are made from unplasticized polyvinyl chloride. The sections and fittings are lighter, easy to fix and do not require painting. The fittings available are the most common used and easy to work with if fitting them as a DIY enthusiast. Half round, square and ogee profile guttering and fittings are available. An ogee is a half-round adaptor used to join gutters of different profiles. Square gutters have a much greater capacity for carrying water than the half-round type. If you need to replace part of the cast iron gutter, there are adaptors available to connect new PVC guttering to either half round or square cast iron guttering. It is important to replace any guttering with a type using a similar size channel.
When the first guttering was installed, its size was calculated to deal with the amount of water likely to come off the roof during a period of heavy rain. If you choose a smaller channel of gutter, you could experience overflowing water damage at times of heavy rain. Larger channels are not a problem, but will be extra unnecessary cost. It is sensible to get a list or brochure showing the entire set of fittings available from a manufacturer before starting to buy parts.
Most domestic rainwater installations use 100mm (4 inch) gutter widths and 62.5mm (2½ inch) downpipes. There should be a slight slope on the guttering leading to the downpipes. A 1 in 600 slope is ideal for guttering, measured from the base of the facia boards.