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OUTDOOR DRAINAGE

Patio Holding Water

A patio holds water when the surface has insufficient fall, local dips, blocked outlets or settlement beneath the paving.

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Stop if water is contaminated or entering the building

Do not handle foul water without suitable protection. Avoid deep excavation near foundations or buried services, and do not redirect water onto neighbouring property.

MOST LIKELY CAUSES

Start with the water route, outlets and ground levels

Incorrect surface fall The patio does not slope toward a safe outlet.
Local settlement Slabs or blocks have sunk and formed a basin.
Blocked channel or outlet Water reaches drainage but cannot escape.
Raised edges or thresholds Borders trap water on the surface.
◫ Symptom variations Match the flooding, ponding or blockage pattern. ⌄
  • Puddles remain after rain
  • One slab area stays wet
  • Water collects near the house
  • Channel drain fills but does not empty
  • Paving rocks or has sunk
✓ Quick checks Safe checks before digging or altering drainage. ⌄
  1. Use a long level to check the fall.
  2. Identify the lowest point.
  3. Clear channels and outlets.
  4. Check for sunken or rocking slabs.
  5. Inspect whether pointing or edging traps water.
Important: Clear existing outlets and map the water path before adding new drains or changing levels.
1 Step 1 — Confirm the intended drainage direction Make the smallest safe correction and retest. ⌄

Water should move away from the building.

2 Step 2 — Clear outlets and channels Make the smallest safe correction and retest. ⌄

Remove silt and test flow.

3 Step 3 — Lift and relay low areas Make the smallest safe correction and retest. ⌄

Correct the sub-base and restore a consistent fall.

⌁ Why the problem happens How rainfall, falls, soil and drainage capacity interact. ⌄

Even a small dip can hold several litres of water. Settlement often creates isolated low spots after installation.

⌘ Advanced checks Further diagnosis for persistent drainage faults. ⌄
  1. Measure falls over several metres.
  2. Check sub-base depth.
  3. Inspect drainage-channel invert level.
  4. Assess impermeable pointing.
  5. Check threshold and damp-proof-course levels.
◇ Tools and information needed Useful items for accurate checks. ⌄
  • Long spirit level
  • Straightedge
  • Rubber mallet
  • Shovel
  • Drain brush
▣ Parts or improvements that may help Common drainage components linked to this problem. ⌄
  • Channel drain
  • Replacement bedding
  • Paving units
  • Jointing compound
  • Drain outlet fittings
! When to call a professional Conditions that should end basic DIY diagnosis. ⌄
  • Water ponds against the house.
  • The patio is above damp-proof-course level.
  • A large area requires relaying.
  • The base has washed out.
  • Drainage must connect to a regulated system.
? Frequently asked questions Common outdoor drainage questions. ⌄

How much fall should a patio have?

Enough to drain consistently away from the building without creating a trip hazard.

Can I drill holes through paving?

That rarely solves the underlying fall or sub-base problem.

Why did it start after a year?

Settlement or washed-out bedding may have created a low spot.