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BCGA3007B. Construct Pitched Roofs (Simple). Types of Roofs we will Cover. Coupled Roofs Gable Roofs. Types of Roofs we will Cover. Non Coupled Roofs Skillion Roofs Lean to Graded Battens. What is a Roof. Roof Structure Definitions. Roof Structure Definitions. Flat Roofing.
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BCGA3007B Construct Pitched Roofs (Simple)
Types of Roofs we will Cover Coupled Roofs • Gable Roofs
Types of Roofs we will Cover Non Coupled Roofs • Skillion Roofs • Lean to • Graded Battens
Flat Roofing • Pitch less than 1:11.5 or 5⁰ • Ceilings usually directly fixed to underside. • Member Sizes Adjusted Accordingly • Usually Single Span, therefore large members • Due to low pitch roof coverings types are limited
Skillion Roofs • Freestanding • Wall at one end is higher • Walls parallel to rafters are tapered
Selecting Members What determines rafter spacing ? Ceiling Linings – if direct fixing Roof Batten Span Required Rafter span Roof Material Mass Ceiling Mass – if direct fixing
Roof Battens Have Span Limits – it is not uncommon where ceilings are unlined to space rafters greater than 650 c to c. Note 70 x 35 will be unsuitable Always Check Notes first to ensure it is suitable
Select Rafter Size Pitch 3° Rafters 600 c to c Step 1 – Calculate Rafter Length i.e. Distance Between Supports Note Horizontal Distance is called run Span = 4200 / cosine 3° = 4200/ 0.9986 = 4206
190 x 45 with maximum overhang of 1550 Rafter Spacing Read Notes Roof Load
Alternate Method to Calculate Rafter Rise 1 in 20 Rafters 600 c to c 230 Rise = Every 20 meters, Rise of 1 meters Rise per m = 1/20 = 0.05 x 4.6 Rise = 0.230 Use Pythagoras to Calculate Rafter Length Rafter = √ (4.62 + 0.2302) = 4.606 To Determine Pitch Pitch =230/ 4600 = 0.05 = Inv Tan 0.05 = 2.862°
Alternative Set Out Length = 4606mm 230 Step 1 – Set out Rafter Length along one edge Remember to allow for overhang Step 2 – Extend Plumb Lines to other edge
Similar Triangles If all angles are the same the triangles are similar All sides are increased by same magnitude
Basic Steel Square Demo Roof Run = 4600 Roof Rise = 210 Ratio =210/4200 = 0.05 Square Run = 500mm Rise = 500 x 0.05 = 25 Alternate Method – Using Similar Triangles Roof Pitch = 3° Tan 3⁰ x 1m =0.052m (Answer is always value for 1) Remember angles stay the same in similar triangles Rise for triangle half size = = tan 3⁰ x 0.500m = 0.026m or 26mm Plumb Cut 3⁰ 1
Graded Batten Roof • Where direct fix ceiling is required to be level on flat roof • Fall is achieved with Battens
Constructing a Skillion Roof Place End Rafters, allowing for soldier trims
Place Rafters at maximum 600 centres (580) Provide Solid Blocking at 1800 centers max
Kliplock Minimum Pitch 1⁰
Trimdeck Minimum Pitch 2⁰
Custom Orb Generally Known as Corrugated Iron Minimum Pitch 5⁰ Not Suitable For Flat Roofs