What Is DPC in Construction: Essential Guide and Materials

June 12, 2024

The Damp Proof Course (DPC) is a crucial element in building construction, designed to restrict the movement of moisture through walls and floors. By preventing moisture penetration, the DPC safeguards the structure from dampness and related issues that could compromise both aesthetics and structural integrity.

Properties of Effective DPC Materials

Imperviousness

The material used for the DPC should be non-porous to prevent moisture from passing through. This ensures that the barrier remains effective over time, protecting the structure from dampness.

"Endike Primary School - 16th February 2012 (5) - External pier construction including DPC" by BSFinHull is licensed under CC BY-NC-ND 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-nd/2.0/.

Strength and Durability

Materials must withstand both dead and live loads without damage. This means that the DPC should be able to bear the weight of the building above it, as well as any additional loads placed upon it during its lifespan.

Dimensional Stability

The DPC materials should maintain their shape and functionality over time, ensuring long-term effectiveness.

Free from Deliquescent Salts

DPC materials should not contain salts like sulfates, chlorides, and nitrates, which can attract moisture and compromise the barrier's effectiveness.

Types of DPC Materials

Flexible Materials

Flexible DPC materials include bitumen felts (hessian or glass fiber-based) and plastic sheeting (polythene). These are commonly used for their ease of application and good performance in various conditions.

Semi-rigid Materials

Semi-rigid DPCs consist of mastic, asphalt, or a combination of materials arranged in layers. These materials provide a balance of flexibility and rigidity necessary for certain types of construction.

"Construction of blockwork footings" by HEA Engineering Subject Centre is licensed under CC BY-NC 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc/2.0/.

Rigid Materials

Rigid DPCs are made from first-class bricks, stones, slate, and cement concrete. These materials are chosen for their robustness and ability to provide a formidable barrier against moisture.

Selection of DPC Materials

Climate and Atmospheric Conditions

When selecting DPC materials, it is important to consider the environment where the DPC will be applied. The materials should be suitable for the specific climate conditions to ensure lasting effectiveness.

Nature of the Structure

The building’s construction and usage must be taken into account when choosing DPC materials. Different structures may require different types of DPCs to address their unique moisture control needs.

Specific Situations

Materials should be selected based on the location within the building. For example, above-ground applications might use different DPC materials than those used below ground level.

Installation Considerations for DPC

Above Ground Level

If the wall thickness is ≤ 40 cm, use any of the mentioned materials. Cement concrete (M15 mix) is commonly used, with added waterproofing materials in damp conditions. Apply two coats of hot bitumen over the concrete DPC for added protection.

"Brickwork below DPC" by HEA Engineering Subject Centre is licensed under CC BY-NC 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc/2.0/.

Floors and Roofs

For larger areas like floors and roofs, flexible materials such as mastic, asphalt, bitumen felts, or plastic sheets are preferred to reduce the number of joints and potential weaknesses.

Differential Thermal Movements

To accommodate thermal movements, use flexible materials like mastic, asphalt, bitumen felts, or metal. These materials can handle the expansion and contraction caused by temperature changes.

Cavity Walls

For cavity walls, use flexible materials such as bitumen felt to bridge cavities over doors and windows, ensuring continuity of the damp-proof barrier.

General Principles for Laying DPC

Coverage

The DPC should cover the full thickness of the walls, excluding rendering. This ensures that all potential moisture paths are blocked.

Preparation

The mortar bed must be level, even, and free from projections to prevent damage to the DPC materials during and after installation.

Continuity

When transitioning from horizontal to vertical sections, a cement concrete fillet (75mm radius) should be provided at the junction to maintain a continuous barrier against moisture.

Placement

Ensure that each DPC layer is placed correctly to achieve a complete and continuous barrier across all parts of the structure requiring damp protection.

Visuals and Diagrams (Referenced)

Figures 1-7 explain various conditions and placements of DPC:

  • Fig 1: Cross-section of DPC.
  • Fig 2: Air Drain.
  • Fig 3: DPC Treatment for basement on undrained soils.
  • Fig 4: DPC plan in a building.
  • Fig 5: DPC Treatment for basement in damp soil.
  • Fig 6: Asphalt tanking.
  • Fig 7: DPC for flooring.
  • Fig 8: DPC for internal walls.

Summary of Key Facts

Definition

A DPC restricts the movement of moisture through walls and floors.

Abbreviation

DPC stands for Damp Proof Course.

Desirable Material Properties

  • Impervious to moisture.
  • Strong and durable.
  • Dimensionally stable over time.
  • Free from deliquescent salts.

Types of Materials

  • Flexible: Bitumen felts, plastic sheets.
  • Semi-rigid: Mastic, asphalt.
  • Rigid: First-class bricks, stones, cement concrete.

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