A DPC or Damp Proof Course is a horizontal layer or barrier installed in a building’s walls, floors, or foundation to prevent moisture from rising through the building’s structure.
It is typically made of materials such as asphalt, bitumen, plastic, or slate, and is inserted at a strategic point in the building’s structure to prevent moisture from penetrating the walls and causing dampness or rot.
Purpose of DPC
- To prevent moisture from rising through the walls and causing dampness.
- To prevent the growth of mold, fungi, and other harmful microorganisms that thrive in damp environments.
- To prevent rot and decay in the building’s wooden components, such as floor joists, wall studs, and roof rafters.
- To prevent the corrosion of metal components, such as steel beams, reinforcement bars, and electrical wiring.
- To prevent the deterioration of masonry materials, such as brick, stone, and concrete, due to moisture penetration.
- To improve the thermal insulation of the building by preventing heat loss through the walls and floors.
- To enhance the fire resistance of the building by creating a barrier that inhibits the spread of flames and smoke.
- To reduce the risk of structural damage to the building caused by moisture-related problems, such as foundation settlement and cracking.
- To improve the overall durability and longevity of the building by protecting it from the damaging effects of moisture.
Causes of dampness in building
1. Rising damp
Occurs when moisture from the ground rises through the walls and floors by capillary action, due to the absence or failure of a damp-proof course.
2. Penetrating dampness
Occurs when water penetrates through the building’s walls, floors, and roofs due to defects in the building envelope such as cracks, gaps, and faulty seals.
3. Leaks
Occur when water enters the building through plumbing, roofs, gutters, or windows due to defects or damage to these components.
4. Poor ventilation
Occurs when there is insufficient air circulation in the building, which can lead to the accumulation of moisture and the growth of mold and mildew.
5. Poor construction
Occurs when the building’s design or construction is inadequate to prevent the entry of moisture or to promote adequate ventilation.
6. Condensation
Occurs when warm, moisture-laden air comes into contact with cooler surfaces such as walls, floors, and ceilings, causing water droplets to form.
Effects of dampness on structure
1. Cracking and spalling of masonry
Dampness can cause masonry materials such as brick, stone, and concrete to crack, flake, or spill, leading to structural instability and aesthetic damage.
2. Increased risk of electrical hazards
When moisture enters electrical lines, it can increase the chances of short-circuiting, which can pose a significant safety risk to occupants.
3. Damage to surface finishes
Dampness can cause the bleaching and flaking of paints, which can affect the appearance of the building and require costly repairs.
4. Infestation by pests
Termites are attracted to damp environments and can cause extensive damage to the wooden components of the building, leading to structural instability and safety hazards.
5. Deterioration of building components
Dampness can cause the disintegration of tiles, damaged plaster, and bricks, which can lead to a reduction in the strength and stability of the building.
6. Corrosion of metal
Dampness can cause metal structural components such as steel beams, reinforcement bars, and electrical wiring to corrode, leading to structural damage and potential safety hazards.
7. Weakening of mortar joints
Dampness can weaken the mortar joints between masonry components, leading to instability and collapse.
8. Efflorescence
Dampness can cause salts to migrate to the surface of masonry materials, leading to the formation of unsightly white stains or crusts.
9. Discoloration and staining
Dampness can cause discoloration and staining of walls, ceilings, and floors, which can be unsightly and difficult to remove.
10. Mold and mildew growth
Dampness can create an ideal environment for mold and mildew to grow, which can lead to health problems for occupants and damage to building components.
11. Structural settlement
Dampness can cause the building’s foundation to settle, leading to structural instability and potential safety hazards.
12. Decay of wood
Dampness can cause wooden structural elements such as floor joists, roof rafters, and wall studs to decay, weaken, and ultimately fail.
Types of DPC
There are several types of DPC (Damp Proof Course), which are used to prevent moisture from rising up through walls and floors in buildings. Here are the 6 common types of DPC list are as follows:
- Physical barrier Damp Proof Course (Membrane Damp Proof Course)
- Chemical Damp Proof Course
- Electro Osmotic Damp Proof Course
- Cavity wall Damp Proof Course
- Integral Damp Proof Course
- Surface Damp Proof Course
1. Physical barrier Damp Proof Course (Membrane Damp Proof Course)
This is a layer of impervious material such as bitumen felt, plastic sheets, or PVC that is installed horizontally within a wall, usually at the base of the wall or between two different materials to prevent moisture from rising.
Materials used:
- Bitumen felt
- Polyethylene sheet
- PVC (polyvinyl chloride) sheet
- EPDM (ethylene propylene diene monomer) rubber sheet
- Plastic or rubberized asphalt membrane
2. Chemical Damp Proof Course
This type of Damp Proof Course involves the injection of a water-repellent chemical into the masonry or concrete to create a barrier against moisture.
It can be either cream or liquid-based and is applied by drilling holes in the masonry.
Materials used:
- Silane/siloxane-based DPC fluids
- Calcium nitrate-based fluids
- Silane/siloxane-based gels
3. Electro Osmotic Damp Proof Course
It is a relatively new technology that uses electrical charges to prevent moisture from penetrating walls and floors.
It works by installing an anode and a cathode at opposite ends of the damp wall, creating an electrical circuit that induces a charge in the water molecules within the wall.
This causes the water molecules to move toward the cathode, which is usually located at the base of the wall, where the moisture is then drained away.
Materials used:
- Titanium mesh anodes
- Platinum-coated titanium anodes
- Graphite anodes
- Copper mesh anodes
4. Cavity wall Damp Proof Course
This is a Damp Proof Course that is installed in the cavity between two walls, usually during construction.
It consists of a strip of impervious material such as metal or plastic that bridges the gap between the two walls to prevent moisture from penetrating.
Materials used:
- Metal cavity trays (usually made of lead or copper)
5. Integral Damp Proof Course
This type of Damp Proof Course is incorporated into the structure of the building during construction, either as a layer of impervious material such as asphalt or as a mixture of water-repellent materials in the concrete mix.
Materials used:
- Water-repellent admixtures
- Hydrated lime
6. Surface Damp Proof Course
This type of Damp Proof Course involves the application of a water-repellent coating or paint on the surface of the wall or floor to create a barrier against moisture.
Materials used:
- Bituminous coatings
- Cementitious coatings
Materials used for DPC
- Bitumen felt
- Bitumen mastic
- Polyethylene sheet
- PVC (polyvinyl chloride) sheet
- EPDM (ethylene propylene diene monomer) rubber sheet
- Liquid damp proof course (a liquid membrane applied by brush or spray)
- Chemical injection damp proof course (a chemical injected into the walls to form a barrier)
- Metal sheet DPC (usually made of lead or copper)
- Concrete or mortar layer
- Plastic or rubberized asphalt membrane
- Bentonite clay waterproofing material
Properties of DPC materials
1. Impermeability
Materials should have a high level of impermeability to prevent water penetration.
2. Durability
Damp Proof Course materials should be durable and able to withstand exposure to moisture, UV radiation, and other environmental factors.
3. Flexibility
Damp Proof Course materials should be flexible enough to accommodate any movement or settling of the building structure without cracking or breaking.
4. Resistance to compression
Damp Proof Course materials should be able to withstand the pressure exerted on them by the weight of the building structure without compressing or losing their effectiveness.
5. Absence of Deliquescent Salts
Damp Proof Course materials should be free from deliquescent salts such as sulfates, chlorides, and nitrates.
Minimum height of DPC
According to IS:7198-1974, for walls and floors above ground level, the minimum height of the damp-proof course should be 150mm above the ground level.
- According to the guidelines set by IS 7198(1974), the damp proofing treatment (DPT) should be laid across the full thickness of the walls.
- This means that the DPT should cover the entire wall, from the inner surface to the outer surface, to create an unbroken barrier against moisture.
For Example,
If the wall is 9 inches thick and spans 12 feet between columns, the DPC should also be 9 inches thick and 12 feet in length to provide a uniform barrier against moisture.
- Laying the DPT across the full thickness of the walls ensures that there are no gaps or weak areas where moisture can seep through, which can lead to various issues, including mold growth and structural damage.
- It is recommended that the DPC should be of even thickness throughout its length.
DPC thickness details
As per the guidelines set by Indian standards, the minimum thickness requirement for DPC is 40mm.
DPC details for building walls
- The recommended ratio for damp-proof course cement mortar is 1:4, which means one part cement and four parts sand.
- The thickness of the DPC should be at least 40mm – 50mm to ensure adequate protection against dampness.
- To increase the effectiveness of the DPC, it is often mixed with a waterproofing compound or cement concrete in a ratio of 1:2:4.
Cement concrete 1:2:4 refers to the ratio of cement, sand, and coarse aggregates used in the mixture.
| Recommended Ratio for damp proof course Cement Mortar | 1:4 |
| Thickness of DPC | 40mm |
| Cement Concrete M15 | 1:2:4 |
DPC details for basement walls
To achieve damp-proof ness in basement walls of residential buildings, a course of DPC in cement-mortar I:4 or cement concrete 1:2:4, and 12 mm minimum thickness should be used.
The recommended ratio for cement-mortar DPC is one part cement to four parts sand, while the ratio for cement concrete is one part cement, two parts sand, and four parts coarse aggregates.
The minimum thickness of the DPC should be 12mm to ensure adequate protection against dampness.
| Recommended Ratio for damp proof course Cement Mortar | 1:4 |
| Thickness of DPC | 12mm |
| Cement Concrete M15 | 1:2:4 |
Steps for applying a damp proof course (DPC)
- Prepare the Surface: Ensure that the surface to be treated is clean, free from debris, and dry.
- Determine the DPC Placement: Identify the appropriate height and location for the damp proof course. Typically, the DPC should be placed between the external and internal walls of the building, about 150mm above the ground level.
- Cut and Install the DPC: Cut the DPC to the required length and place it in the designated position. Ensure that the DPC is placed in a continuous line without any gaps or breaks. The thickness of the DPC should be at least 12mm.
- Secure the DPC: Fasten the DPC to the wall using masonry nails, adhesive, or other fastening methods, depending on the type of DPC and wall material.
- Seal the Joints: Ensure that all joints are sealed tightly to prevent water infiltration.
- Backfill: Once the DPC is installed, backfill with clean soil or other material to cover the DPC and protect it from damage.
- Check for Adequate Protection: Inspect the DPC after installation to ensure that it provides adequate protection against moisture ingress.
Advantages of DPC
- Prevents moisture from penetrating walls and floors, thereby reducing the risk of structural damage.
- Helps to prevent mold growth and other moisture-related problems that can impact the health of the occupants.
- Increases the longevity of the building by protecting it from water damage.
- Helps to maintain a comfortable and healthy living environment by reducing humidity and condensation.
- Protects the building against rising dampness and capillary action.
- Prevents the deterioration of wall finishes and coatings due to moisture.
- Increases the resale value of the property by protecting against dampness.
- Reduces energy costs by preventing heat loss through damp walls.
