Purpose and Application: Sawn Timber Firrings are essential for creating a slope on flat roof systems. Despite the term "flat roof," building regulations mandate a slight incline to prevent water pooling. Typically, these firrings are nailed onto ceiling or roof joists to establish the necessary slope.
Customization and Specifications: Flat Roof Firrings are usually cut to order, tailored to the specific requirements of each project. They are available in various heights and lengths, with common sizes being 50mm, 100mm, and 150mm. However, custom sizes can be provided to meet unique project needs.
Usage in DIY and Building Projects: For most DIY enthusiasts and general building tasks, firrings that taper to 0mm are preferred. This means the firring starts at a specified height at one end and reduces to 0mm at the other, creating a gradual slope.
Building Regulations for Flat Roofing Systems: Building regulations stipulate a minimum slope to ensure proper drainage. Each roofing material may have additional specific recommendations, typically provided by the architect or the manufacturer.
Nominal vs. Regularised Timber Sizes: It's important to note that timber is often measured as a nominal size. Regularised timber, such as that used for firrings, usually finishes around 5mm smaller than its advertised size (e.g., 50mm becomes 45mm). Building regulations specify falls in units, not timber sizes.
Examples and Calculations for Firring Sizes: To comply with building regulations and BS6229 standards, specific guidelines and calculations are necessary. A 90mm fall over 3600mm meets the 1:40 fall regulation. It’s crucial to note that not all firrings need to taper to 0mm. For instance, a 100mm to 10mm firring can provide a suitable 90mm drop, and some roofers might prefer this over a "to 0mm" firring.
Ensuring Compliance and Accuracy: When referencing building regulations or BS6229, always verify with the latest updates from the relevant government department or professional body to ensure compliance with the most current guidelines.
