How far below the damp-proof course should a patio be?

Approved Document C sets the damp-proof course at least 150mm above finished ground level, so paving against a house should sit at least that far below the damp-proof course line. Where a threshold makes that impossible, the usual answer is a drainage channel and a lowered margin rather than raising the paving.

Can I just add a drainage channel and leave the levels alone?

A channel helps by catching runoff before it reaches the wall, and it is sometimes the only option at a door threshold. It does not fix a bridged damp-proof course, though — if the paving and its bedding sit above that line, moisture still has a path into the masonry.

Is the damp inside definitely caused by the patio?

Not necessarily, and it is worth being honest about that. A bridged damp-proof course is a common cause of damp at skirting height on an external wall, but a leaking gutter, a failed downpipe, a bridged cavity or a plumbing leak can all look identical inside. Correcting the levels removes one certain cause.

Do I need planning permission to relay a patio lower?

A rear patio at ground level is normally permitted development. Raised platforms and decking have their own height rules, and paving a front garden has separate drainage conditions — the Planning Portal covers both.

High risk

Updated 30 August 2026

Patio Drains Towards The House

Rain runs off the patio towards the wall instead of away from it, and the paving sits level with or above the damp-proof course.

Find a landscaper

What's happening?

This is a levels fault, not a paving fault, and re-laying the same patio at the same height will not fix it. Two things have to be right where hard landscaping meets a house. The paving must fall away from the wall so surface water runs off rather than towards the brickwork. And the finished surface must sit low enough that the damp-proof course is still doing its job: Approved Document C of the Building Regulations puts the damp-proof course at least 150mm above the finished ground level, so a patio built up to or over the airbricks and the damp-proof course has bridged the very barrier that keeps ground moisture out of the wall. Once bridged, water enters the masonry above the barrier and shows up inside as damp at skirting height.

What usually causes it?

The patio laid to fall towards the house instead of away, often to match an existing threshold height
Paving built up over successive re-lays until it sits level with or above the damp-proof course
Airbricks buried or blocked by the new paving, stopping sub-floor ventilation
No drainage channel where the paving meets the wall, so runoff has nowhere to go but the brickwork
Mortar, hardcore or debris packed against the wall, bridging the damp-proof course even where levels look right
A patio laid over an old one rather than the old one being taken up
Downpipes or a rainwater gully discharging onto the patio and running back to the wall

Is it dangerous?

Not a physical hazard, but a real risk to the building. A bridged damp-proof course puts moisture into the wall continuously, which shows up as rising damp inside, ruined plaster, blown paint and mould in the room behind. Buried airbricks stop the sub-floor from breathing, which promotes rot in a suspended timber floor and, where a gas appliance depends on that ventilation, is a safety issue in its own right. Water standing against the wall in winter also lifts the risk of frost damage to the brick face.

Can I fix it myself?

Measure before assuming. Find the damp-proof course — usually a visible mortar line or a black strip two courses above the paving — and measure down to the patio surface. If that gap is less than 150mm, the levels are wrong. Pour a bucket of water in the middle of the patio and watch which way it runs. Clear any soil, mortar or debris heaped against the wall, and dig out and clear any buried airbricks so they can breathe again. Beyond that, correcting the fall or lowering the paving means taking the patio up, which is not a DIY afternoon.

When should you call a landscaper?

Call a landscaper promptly if the paving is level with or above the damp-proof course, if the airbricks are buried, or if damp has already appeared on the inside of that wall. Do not put it off to next summer — the wall is absorbing water every time it rains. If damp is already showing internally, get the levels corrected first, because replastering before the water is stopped simply ruins the new plaster too.

What will the landscaper actually do?

Locate the damp-proof course and measure the shortfall between it and the finished paving level
Lift the paving and, where needed, reduce the sub-base so the finished surface sits at least 150mm below the damp-proof course
Re-lay the paving to a positive fall away from the house, typically shedding water to a channel or a permeable margin
Form a drainage channel or aco run along the wall line and connect it to a soakaway or surface water outlet
Clear and reinstate airbricks, adding periscope vents where the level cannot be dropped enough, and cut back mortar, hardcore and soil so nothing bridges the damp-proof course
Check where downpipes discharge and redirect them into the new drainage rather than onto the paving

Frequently asked questions

We’re happy to answer all your questions.

Sources & References

Garden Floods Every WinterCaution Garden Steps Uneven And UnsafeCaution Decking Slippery, Soft And BouncyCaution

Need a landscaper?

Compare local landscapers on Tradehand — coverage areas, accreditations and phone numbers, no middleman.