Understanding Damp Proof Course (DPC) and Its Importance in Building Projects
The damp proof course (DPC) is a critical component in construction that serves as a barrier to prevent moisture from penetrating walls and floors, ensuring the longevity and quality of the building. This article delves into the necessity of DPCs, their roles in different construction scenarios, and common issues related to dampness in buildings.
What is a Damp Proof Course?
A Damp Proof Course, or DPC, is a continuous barrier designed to prevent moisture from rising up through the walls and floors of a building. Traditionally, early DPCs were made of physical materials like slate, tile, or a heavy gauge of plastic tarred felt, or metal, but modern construction typically uses heavy gauge plastic or polyethylene sheets.
Where is a Damp Proof Course Used?
DPCs are used in both walls and flooring to create a moisture barrier. In buildings, they are commonly placed around 6 inches above the external ground level, often continuous with the damp proof membrane (DPM) that protects the ground slab. DPCs are also essential in cavity construction, where the inner and outer leaves of walls enclose around window openings and similar features.
Why is a Damp Proof Course Necessary?
MOISTURE can cause a myriad of serious issues within buildings, from moisture around windows to slip hazards. These can include:
Damp Patches Mildew Growth leading to respiratory allergies Mold and Mildew Salt Stains Damage to Surface Finishes leading to an unsightly appearance Fabric Corrosion and Decay Flooring and Insulation Damage Floors and Electrical FailuresSeveral primary factors can lead to persistent dampness in buildings:
Condensation, both on surfaces and in interstices Penetrating Damp, which can be due to structural defects or faulty DPCs Rising Damp, caused by capillary action drawing moisture through the porous parts of the buildingConstruction Standards and Specifications
For new construction, DPCs are a legal requirement under Building Regulations. Part C of the Building Regulations, which covers site preparation and resistance to contaminants and moisture, mandates that DPCs should be continuous with the floor DPM and at least 150 mm above the external ground level for external walls. Suspended timber floors also need DPCs between the timber and moisture-retaining ground materials.
Rectifying Dampness Issues in Older Buildings
In older buildings, the absence of a DPC can be remedied by introducing a moisture-impermeable layer, either through the installation of a new DPC or the application of water-repellent chemicals. However, dampness could also be due to structural leaks or faulty construction, such as cracks, rather than rising damp. It is essential to identify and correct any such issues before inserting a DPC. In cases where a 150 mm DPC is not feasible, external drainage solutions like French Drains might be necessary.
Conclusion
A damp proof course is a vital element in ensuring the protection and longevity of a building. Whether in new or older structures, understanding the necessity and proper installation of DPCs can significantly enhance the overall quality and lifespan of a building. By addressing moisture issues, building owners can prevent the myriad of problems caused by dampness, leading to a more secure and reliable living environment.
References
For detailed standards, refer to BS 8215:1991, Code of Practice for Design and Installation of Damp-Proof Courses in Masonry Construction.