Cavity walls



Damp-Proof Courses Introduction

The installation of the damp-proof courses in a cavity wall construction is an important element in ensuring the building performs to a satisfactory level. Detailed below are installation details in areas where there is a high risk of water ingress.

Sill Details

Diagram C36 - Typical DPC installation detail around window cills

Diagram C37 - Typical DPC installation - concrete cill

Diagram C38 - Typical DPC installation - brick cill

Jamb Detail

Frames must be installed behind the outer leaf and care should be taken to ensure frames are installed plumb, level, square, and fitted to acceptable tolerances.

Diagram C39 - Typical DPC installation - jamb detail

DPC Location

To ensure dampness cannot penetrate inside the building it is important to ensure that the DPC is provided in the correct location.

Diagram C40 - Correct location for DPC to prevent damp penetration

Pressed Metal Lintels

Diagram C41 - Pressed metal lintels - stepped DPCs above openings

Pre-Stressed Concrete Lintels

Provide stepped DPCs to all openings in cavity walls or proprietary cavity tray DPCs.


Weepholes should be provided above openings at a maximum of 450 mm centres.

Diagram C43 - Weepholes in unrendered outer leaf

In the case of brick, fairfaced blockwork, or any surface where the outer leaf is unrendered, weepholes should be provided at no more than 450 mm centres. Also, lodging of mortar droppings in DPC should be avoided.

Typical Stone-Facing DPC Details

Diagram C44 - Typical DPC detail - window/door head for stone facing onto cavity wall

Diagram C45 - Typical DPC detail - cill detail for stone facing onto a cavity wall

Diagram C46 - Typical DPC detail - window/door reveal for stone facing onto a cavity wall

Roof Abutments

Careful detailing of damp-proof courses and flashings is required for flat roof and mono-pitch roof abutments. These types of abutments can occur at balconies, porches, garages etc. In all cases, cover flashings should be built-in under the stepped DPC.

Metal used for flashings should be non-ferrous. In cases where lead is used, the lead should be at least a code four (colour code blue). Laps for flashings should be greater than 100 mm (150 mm in locations prone to high wind and rain) and individual lengths should be less than 1.5 m.

Diagram C47 - Typical DPC detail - flat roof abutment

Diagram C48 - Typical DPC detail - mono pitch roof abutment


If DPC is not installed correctly, any moisture that drains down the cavity will seep through and show up as damp on the ceiling of habitable rooms inside.