Minimum DPC height above ground level
The 150mm rule, what counts as finished ground level, and the site conditions that quietly bridge it.
Short answer
A damp proof course should be at least 150mm above the finished ground level next to the wall. That height keeps rain splash and standing water below the DPC line. Lower heights are only acceptable where the design provides an equivalent barrier, such as a drained threshold detail at an accessible entrance.
Key figures
| Requirement | Value | Basis |
|---|---|---|
| Minimum DPC height above finished ground | 150 mm | Approved Document C |
| Minimum DPC lap at joints | 100 mm | Approved Document C |
| Cavity fill height below DPC | at least 225 mm below the lowest DPC | Approved Document C |
What the requirement actually says
Approved Document C requires walls to resist the passage of moisture from the ground. The practical expression of that in low-rise housing is a continuous damp proof course, linked to the floor damp proof membrane, set a minimum of 150mm above the finished ground level adjoining the wall.
The number is not arbitrary. 150mm is the height at which rain splashing off a hard surface stops reliably reaching masonry above the DPC line. Reduce it and you are relying on the render, the mortar and the brick to do a job they were never designed to do.
Finished ground level, not the level on the day
The measurement is taken against the ground level once external works are complete. That is the single most common source of dispute: the DPC is correct at superstructure stage, then the landscaper raises the patio, the driveway gets a second bind and wear course, or topsoil is graded up against the wall.
On a site with any change in level, record the DPC height at brickwork stage with a photo and a tape in shot, then re-check the same wall after external works. Two records, months apart, settle almost every argument about who raised the ground.
How it fails in practice
- Paving laid to the underside of the DPC so surface water sits against the wall.
- Render or a sand-cement plinth carried down across the DPC, bridging it.
- Mortar droppings on cavity trays and wall ties forming a path over the DPC.
- A flower bed or turf built up above the DPC after handover.
- Sub-floor vents blocked or buried by the same regrade that buried the DPC.
Checking it on site
This is a two-minute check with a tape and a straight edge. Measure from the finished ground surface to the visible DPC line at the lowest point of the ground adjacent to the wall, not the average.
How to check it
- Find the lowest adjacent ground level. Walk the elevation and identify the point where the external surface is highest relative to the DPC line.
- Measure to the DPC. Measure vertically from the finished surface to the underside of the visible DPC. Record the reading with a photograph and the tape in shot.
- Check for bridging. Look for render, mortar, paving haunching or soil crossing the DPC line at any point along the wall.
- Re-check after external works. Repeat the measurement once driveways, patios and soft landscaping are complete, because that is the level the requirement is judged against.
Common questions
Is 150mm a legal minimum or best practice?
Approved Document C is guidance on how to meet the functional requirement of the Building Regulations. 150mm is the accepted way of showing compliance; anything less needs a design that demonstrates equivalent resistance to moisture.
Can the DPC be lower at a doorway?
Yes, at an accessible threshold a lower step is normally unavoidable. That case is handled by a designed threshold detail with drainage, a proprietary threshold DPC and a cavity tray over, not by simply dropping the DPC height.
What if the paving has already been laid too high?
The usual remedies are lowering the paving, or forming a drained channel against the wall so the effective ground level next to the masonry drops back below the 150mm line. Sealant along the wall is not a remedy.
Basis in regulation
Part C
Approved Document C — site preparation and resistance to contaminants and moisture
Read the source
Last reviewed 2026-08-21.