How do I find my damp proof course from outside?

Look at the brickwork a couple of courses above ground for a mortar joint that looks different, a thin dark line, or a course of slate or engineering brick. That is the line the ground outside should be sitting at least 150mm below.

My patio is higher than the damp proof course. Does it all have to come up?

Often not all of it. Forming a drained channel along the wall — dropping the level next to the building and giving the water somewhere to go — solves most cases without lifting the whole patio.

Is bridged damp the same as rising damp?

No, and confusing them is expensive. In bridged damp the barrier is intact and water is going around it, so the fix is outside the wall. In rising damp the barrier is missing or defective, which is what remedial damp proofing addresses. The symptoms inside can look identical.

Can render cause damp?

Yes, in two ways. Taken down past the damp proof course it bridges it directly. And cement render on a solid wall stops the wall evaporating moisture from its outer face, so water that used to leave the wall now comes inside instead.

Caution

Updated 30 August 2026

Bridged Damp Proof Course

Low-level damp inside where a path, patio, flower bed or render outside has been built up over the damp proof course.

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What's happening?

A bridged damp proof course is the most fixable cause of low-level damp, and the most frequently mistaken for rising damp. The barrier in the wall is intact and doing its job — but something has given water a route around it. Outside, the usual culprit is height: a path, patio, drive, decking or flower bed built up so that ground sits at or above the barrier, so water enters the wall above the line the barrier protects. Render taken down past the damp proof course does the same thing, as does a cavity part-filled with mortar droppings or rubble. Inside, a floor screed laid up over the barrier bridges it just as effectively. The guidance sets the external damp proof course at least 150mm above adjoining ground for exactly this reason.

What usually causes it?

Path, patio, drive or decking laid up to or above the damp proof course line
Flower bed, raised planter or accumulated soil and mulch banked against the wall
External render or a plinth carried down across and below the damp proof course
Internal floor screed or a new solid floor laid up over the barrier at the wall junction
Mortar droppings, rubble or spilled cavity insulation bridging the cavity above the barrier
A porch, step or lean-to added later with its floor above the original damp proof course
Retrofitted external wall insulation taken below the damp proof course line

Is it dangerous?

No, and this is the good news case in this category: the wall base gets wet, the plaster and skirtings suffer, mould can follow, but the remedy is external and mechanical rather than injected. What makes it worth acting on is that it is usually cheap to fix and frequently mis-sold as something expensive.

Can I fix it myself?

More than in any other damp problem here. Find the damp proof course on the outside — commonly a distinct mortar joint or slate course a couple of brick courses up — and measure down to the ground. Clear soil, mulch, gravel and leaf litter back below it. Cut back a flower bed. Where a path or patio is the problem, digging a channel along the wall to drop the level and provide drainage is a genuine fix and within reach of a determined DIYer. What needs care: do not simply seal the wall face, do not undermine a foundation while digging out, and leave render removal below the line to someone who will make good properly.

When should you call a damp proofer?

Call a damp proofer where you can see bridging but want the diagnosis confirmed before spending on landscaping, where the internal floor appears to be bridging the barrier, or where a suspected bridged cavity needs opening up to check. Also call if you have been quoted for injection on a wall where the ground outside is clearly high — that is exactly the case where the cheaper remedy is the correct one, and it is worth a second opinion.

What will the damp proofer actually do?

Locate the damp proof course externally and measure the ground and floor levels against it
Correlate the internal damp pattern with where the bridging actually is
Open up to check the cavity for mortar droppings, rubble or dropped insulation, and clear it
Reduce external ground levels and form a drained margin along the wall so run-off is carried away
Cut back render, plinths or external insulation that cross the damp proof course, and detail the stop correctly
Allow the wall to dry and only then make good the internal plaster and skirtings

The levels that matter

Most bridging is a levels problem, and the levels are set out in the moisture guidance for external walls. Checking these before commissioning any damp work is the cheapest survey there is.

The damp proof course in an external wall should be at least 150mm above the level of the adjoining ground.
The damp proof course should be continuous with any damp proof membrane in the floors.
In an external cavity wall, the cavity should be carried down at least 225mm below the lowest damp proof course, or a damp proof tray provided instead.
Where a damp proof tray is used, weep holes at roughly 900mm centres let water out through the external leaf.

Frequently asked questions

We’re happy to answer all your questions.

Sources & References

Rising DampCaution Failed Damp Proof CourseCaution Wet Rot In Skirting BoardsCaution

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