Construct Pitched Roofs (Simple) 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 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

Selecting Members

For types of roof we will cover today

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°

Complete Following

Answers

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

Similar Triangles

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

Install Soldier Trims

Cut Overhangs & Install Verge Trims

Install Wall Blocking

Install Fascia

Kliplock Minimum Pitch 1⁰

Trimdeck Minimum Pitch 2⁰

Custom Orb Generally Known as Corrugated Iron Minimum Pitch 5⁰ Not Suitable For Flat Roofs Maximum Recommended Support Spacings Type of Span Thickness (mm) BMT 0.42 0.48 Roofs Single Span End Span Internal Span Unstiffened Eaves Overhang Stiffened Eaves Overhang Walls Single Span End Span Internal Span Overhang 700 900 1200 200 300 1800 2500 2700 200 800 1300 1700 250 350 1800 2700 2700 250