If you are replacing or installing uPVC guttering, the main choice is usually between half round, square and deepflow.
For most normal domestic jobs, the choice between half round and square is mainly about appearance and matching the property. Deepflow is the option to look at when you genuinely need more rainwater capacity.
Half round or square guttering?
Half round guttering has the traditional curved profile. Square guttering has a flatter, more angular look. If either system is suitable for the roof, we normally recommend choosing the style you prefer or matching what is already on the property.
Freeflow's published figures do give square guttering a slightly higher flow capacity than half round. With a central outlet and a 1:600 fall, half round is rated at 2.43 litres per second and square at 3.03 litres per second. In practice, we would not normally tell a customer to choose square purely for that difference. If capacity is the reason for changing system, Deepflow is the more meaningful step up.
When should you use Deepflow guttering?
Deepflow guttering is deeper and carries considerably more water than the standard half round and square profiles. Freeflow rates its 116mm x 77mm Deepflow system at 4.60 litres per second with a central outlet and a 1:600 fall.
That makes it the better choice where the roof area, gutter run or expected water volume needs extra capacity. If an existing gutter regularly overflows, first make sure the system is clear, supported correctly and falling towards the outlet. If those basics are right and capacity is still the problem, Deepflow is the system designed to give you more headroom.
How much difference does the outlet position make?
The gutter profile is only part of the calculation. Freeflow's own figures show that outlet position makes a large difference to the amount of water a run can carry.
| System | Central outlet, 1:600 fall | End outlet, 1:600 fall |
|---|---|---|
| Half Round | 2.43 L/s | 1.21 L/s |
| Square | 3.03 L/s | 1.55 L/s |
| Deepflow | 4.60 L/s | 2.29 L/s |
So if you are planning a new system, do not choose the gutter profile in isolation. The roof area, length of run, fall and outlet position all affect the finished capacity.
Round or square downpipe?
Freeflow uses 68mm round and 65mm square downpipe systems. For a normal domestic installation, we treat this mainly as a style and matching decision rather than a performance choice.
If you are fitting a complete new system, choose the downpipe style that suits the guttering and the property. If you are repairing an existing system, match what is already there. You can see our downpipes and fittings together here.
Will new gutter fittings fit old guttering?
Most common uPVC gutter sizes are fairly standard, so replacing square with square or half round with half round will often work. We still do not recommend buying replacement fittings on appearance alone.
If possible, bring a small section of the old gutter or the fitting you are replacing with you. That lets you physically match the profile and make sure the new fitting clips onto the old system correctly before buying the rest of the job.
This is especially useful on older systems where the original manufacturer may not be obvious.
Which one should you choose?
Choose Half Round if you want the traditional curved style or need to match an existing half round system.
Choose Square if you prefer the more angular appearance or need to match existing square guttering.
Choose Deepflow when you need a genuine increase in rainwater capacity rather than simply a different shape.
If you are starting from scratch, browse our full guttering, downpipes and fittings range. Once you have chosen the system, our guide to fitting guttering and downpipes covers the installation order, fall, bracket spacing, cutting and final water test.
