Why Stockton patios hold water
Three things combine in most local gardens.
The ground. The British Geological Survey maps glacial till, a stiff, stony boulder clay, under much of west Stockton, including Fairfield, Elm Tree and Eaglescliffe. Under central Billingham it maps softer glaciolacustrine clay and silt, laid down in a lake at the end of the last ice age, and under Norton sandier lake deposits. Till and lake clay both drain slowly; the sandy deposits in Norton drain better but vary over short distances.
Flat gardens. Much of Stockton is low and level. On a flat plot, water goes nowhere unless the patio is built with a fall.
Surface water. The Environment Agency's long-term flood risk service shows many low points across the borough where rainwater collects after heavy storms, even well away from the Tees and its becks. A patio built at the bottom of one of these spots will collect water from neighbouring gardens as well as its own.
The basics: levels and falls
- Fall away from the house. We build a gentle fall, typically around 1 in 60 to 1 in 80, so water runs off without the slope being noticeable underfoot.
- Stay below the damp-proof course. Building regulations guidance on damp proofing expects the damp-proof course to be at least 150mm above adjoining paving. If the finished patio has to sit closer than that, a drain against the house is needed.
- Keep air bricks clear. Never raise a patio over an air brick; it ventilates the floor void.
- No back-falls. A patio that falls towards the house, even slightly, sends every storm against the wall.
Where the water should go
Building regulations guidance in Approved Document H sets an order of priority for rainwater from buildings and paved areas: first an adequate soakaway or other infiltration system; if that is not practicable, a watercourse; and only then a sewer. We follow the same thinking for patios.
1. Let it soak in nearby
For a modest patio, the simplest answer is a fall towards a lawn, planted border or a gravel strip along the low edge. On Norton's sandier ground this often works well. On boulder clay, the border needs to be wide and the patio small, or the border just becomes a bog.
2. A channel drain to a soakaway
A slot or channel drain along the low edge collects the run-off and pipes it to a soakaway, a pit or crate system that lets water seep into the ground. On clay we test first: a percolation test shows how fast the ground absorbs water, and stiff till often fails it. Soakaways are normally kept at least five metres from buildings, so they need a reasonably long garden.
3. Connect to a surface water drain
If the ground will not take the water, the channel can connect to an existing surface water drain or rainwater gully, provided it is a surface water system and not the foul sewer. Rainwater should never be connected into a foul drain.
4. Permeable paving
A permeable patio lets rain pass through the joints or surface into a deep, open-graded stone base that stores it and releases it slowly into the ground. The government's sustainable drainage standards describe this kind of storage approach. On free-draining ground it can be the neatest answer; on clay the base needs to be deeper, and sometimes an overflow pipe is added for heavy storms.
Front gardens and the five square metre rule
If you are paving at the front, the national rule applies: more than five square metres of impermeable surface draining onto the road needs planning permission. The government's guidance on permeable surfacing explains the options. In Stockton's conservation areas, Article 4 Directions can also remove the right to lay a hard surface at the front, so check first. Our conservation areas guide covers this.
A note on your water bill
Northumbrian Water's sewerage charge includes surface water drainage. It explains that if your property is not connected for surface water, because roof and paving water goes to a soakaway, you may be entitled to a rebate. Sending patio water to a soakaway rather than the sewer is one small part of that picture.
Signs your existing patio has a drainage problem
- Puddles that are still there hours after rain.
- Green algae and moss along one edge or against the house.
- Damp patches on internal walls near the patio.
- Slabs sinking where downpipes discharge onto them.
- Water running into a garage, utility or back door.
Some of these can be fixed with a channel drain alone. Others mean the patio was laid with the wrong fall or on a failed base, and lifting and relaying is the lasting fix.
How we design drainage into a new patio
- Survey the levels of the house, damp-proof course, air bricks, doors and the garden.
- Check the ground when we dig, and test it if a soakaway is being considered.
- Find the existing drains and confirm whether they are surface water or foul.
- Design the fall and outlet together, so water has a planned route from the first day.
We cover the build itself on our pages for patio slabs and porcelain patios, and a sloping garden needs extra thought, covered in our guide to patios on a slope.
Questions people ask
How do I fix a patio that floods?
Find out why first. If it falls towards the house or has no outlet, a channel drain along the low edge can help. If slabs have sunk or the base has failed, the patio needs lifting and relaying with the right fall.
Should a patio be level or sloped?
Sloped, gently. A fall of roughly 1 in 60 to 1 in 80 away from the house lets water run off but still feels level underfoot.
Can patio rainwater go into the sewer?
It can go to a surface water drain where there is no practical way to let it soak away. It should never be connected to the foul drain that serves toilets and sinks.
Is permeable paving a good idea on clay?
It can be, but the base must be deep enough to store water while the clay slowly absorbs it, so it costs more. On stiff till, a conventional patio with a channel drain is often simpler.
Sources: GOV.UK: Approved Document H, drainage and waste disposal; GOV.UK: sustainable drainage systems, non-statutory technical standards; GOV.UK: permeable surfacing of front gardens; Environment Agency: check long-term flood risk; BGS Geology Viewer; Northumbrian Water: charges and surface water drainage.