The figure below shows selected code sections that must be considered when designing this type roof.įigure R802.5. Ridge boards shall be at least 1 inch nominal thickness and not less in depth than the cut end of the rafter (IRC section R802.3).Ĭhapter 8 of the International Residential Code (IRC) prescribes the elements for a type of roof frame known as a 'compression roof'. 6 FUTUREBUILD® LVL RESIDENTIAL DESIGN GUIDE 0800 585 244 .n 2.1 PRODUCT AVAILABILITY Table 1: Futurebuild® LVL Standard Product Range Product Depth (mm) Thickness (mm) Length (0.6 m increments 45 63 90 where indicated) hySPAN® 150 2.4 13.2 m 170 200 240 300 360 400 450 600 hy90® 150 4.8 7. Ridge boards can only be used in roofs with slopes from 3 in 12 up to 12 in 12. Ridge beam sizing is based on the span of the beam between supports, and the amount of roof load supported by the beam.Ī ridge board is a non-structural member that serves as a prop for opposing rafters to rest against and connect to. Ridge beams are required by code if the roof slope is less than 3 in 12 (IRC section R802.3). By using the simple formula provided in this guide and tailoring it to your specific roof specifications, you can confidently select the right size for your ridge beam.A Ridge Beam and a Ridge Board are both located at the ridge but they serve very different purposes for very different applications.Ī ridge beam is a structural member used to support the ends of the rafters at the ridge, transferring it's loads to posts or gable end walls. ConclusionĬalculating the ridge beam size is a critical step in ensuring the structural stability of your roofing project. Q3: Can I round the calculated ridge beam size to the nearest standard size available in the market?Ī3: Yes, it’s common to round the calculated size to the nearest standard beam size that is readily available in your area. Q2: Do I need any special tools to calculate the ridge beam size?Ī2: No, all you need is the formula and the measurements of your roof’s slope, length, width, and the allowable stress of the materials used. Roof 0.4 kPa Dead Loads Span/300 or 20mm 1200mm for sheet roofs Live Load 0.25 kPa Live loads Span/250 330mm for tile roofs 1.1 kN Wind load Span/150 Snow Load 0. Simply plug in the appropriate numbers to calculate the ridge beam size. Q1: What if my roof has a different slope or allowable stress?Ī1: The formula can be used with any roof slope or allowable stress value. Now that we’ve covered the formula and an example, let’s address some frequently asked questions to clarify any doubts you might have. So, for this example, the calculated ridge beam size (RB) is approximately 0.36 inches. Allowable Stress (F): 1,000 pounds per square inch (PSI).Roof Slope (S): 4:12 (or 0.33 as a decimal).Suppose you are designing a roof with the following specifications: For example, you can span a 1 grade (no knots) southern yellow pine joist a greater distance than a 2 grade of the same species (with knots). The lengths and sizes of joists vary depending on the species and quality of the lumber used. Now, let’s explore how to use this formula step by step with a practical example. Considerations when using the Rafter and Joist Span Tables. It’s an important factor in ensuring the structural integrity of the ridge beam. F (Allowable Stress): Allowable stress is a measure of how much stress or load a material can withstand safely.W (Building Width): Building width is the horizontal distance between the exterior walls of the building.L (Roof Length): Roof length is the horizontal distance from one end of the roof to the other.It’s typically measured as a ratio of vertical rise to horizontal run. S (Roof Slope): Roof slope refers to the angle at which the roof inclines. RB (Ridge Beam Size): This is the value we want to find, representing the required size of the ridge beam.My plan was to nail and glue 2×12’s with 1/2 ply wood in the middle to make a 48ft ridge board this will be supported by 4×4’s and 2×6’s. Formulaīefore diving into the calculation process, let’s break down the components of the ridge beam sizing formula: I will be using 6×6 poles on 8ft centers with 2×6 framing in between, with 1/2 osb on the outside. By the end of this article, you’ll have all the tools and knowledge necessary to determine the ideal ridge beam size for your roofing project. We’ll explain each component of the formula, provide practical examples, address common questions in the FAQs section, and even offer a ready-to-use Ridge Beam Calculator in HTML code. In this comprehensive guide, we will walk you through the process of calculating the ridge beam size using the formula:
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