There are three main options when choosing your gutters: perishing, rusting or just plain old breaking, in other words: PVC, galvanised steel or fibre cement.
Ok so mayhaps a touch negative but I want to make the point that you have to treat your building's rainwater goods like the clutch on a car - they will work well for many years but will eventually need replacing.
"Plastic" gutters are pretty much the standard now, reasonably economical and easy to fit they do the job well.   They are available in a wide range of sizes but 170mm half round is the most commonly specified, anything less should be avoided - there is a big difference in capacity between a 130mm and a 150mm gutter
We specify "Hunter HighFlo", a UK made brand widely available should you ever require spares in a hurry.   Please try us should you be replacing gutters as our prices are highly competitive.
For big span buildings or where the number of downpipes has to be limited it is possible to obtain an 8" (200mm) variant which can handle enormous volumes of water.
Some people really don't like PVC gutters but we have fitted vast quantities with no problems, the key is to provide sufficient appropriately spaced outlets and to use plenty of brackets which are essential to keep the gutter in shape.   Where we have seen problems it is usually excessive spacing between the brackets allowing the gutter to droop and distort that is the cause.   Eventually however they are affected by UV radiation and become brittle with perished seals when replacement is the only sensible option, although modern products have better protection agents incorporated during manufacture and you can expect many years of life.
To sum up, PVC gutters are relatively cheap, simple to install and repair if accidentally damaged, require no maintenance but will probably require replacement after 25 years or so.
PVC rainwater goods are only of use for standard gutter arrangements, if you have a valley between two roofs or a boundary wall situation then you need to be looking at steel or fibre cement.
Steel gutters have the advantage that they can be designed and made to suit specific requirements rather than being restricted to fixed sizes and shapes which makes them ideal for valley and boundary walls, however they are just as useful as a replacement for standard gutters and are particularly suitable where you can't practically fit many downpipes.
They can be supported in brackets or designed to freespan post to post in single sections.
The galvanising will last a good time but if you give them an occasional slap of bitumen paint inside and clear out the leaves then they will outlast you, they are a bit more expensive than PVC but a good investment.
Summmary; more expensive than PVC and a pain to repair if accidentally damaged but they will last forever if (and only if) you maintain them.
Before PVC was invented these were the equivalent, available off the shelf with a wide range of fittings, rust proof and relatively easy to fit.   Unfortunately they eventually get very brittle and when you try to fix them you just end up breaking more of the stuff.
You can still buy them but they are now pretty expensive because of the low sales volume.   If you love them (or want a 'retro' look) then by all means go ahead but we see no real advantage over PVC that makes it worth paying the difference.   Actually I can only remember fitting them on a new build twice in the last 20 years.
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