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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

BCGA3007B

Construct Pitched Roofs

(Simple)


Types of roofs we will cover
Types of Roofs we will Cover

Coupled Roofs

  • Gable Roofs


Types of roofs we will cover1
Types of Roofs we will Cover

Non Coupled Roofs

  • Skillion Roofs

  • Lean to

  • Graded Battens





Flat roofing
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
Skillion Roofs

  • Freestanding

  • Wall at one end is higher

  • Walls parallel to rafters are tapered


Selecting members
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
Select Rafter Size ceilings are unlined to space rafters greater than 650 c to c.

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 ceilings are unlined to space rafters greater than 650 c to c.

Rafter Spacing

Read Notes

Roof Load


Alternate method to calculate rafter
Alternate Method to Calculate Rafter ceilings are unlined to space rafters greater than 650 c to c.

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
Complete Following ceilings are unlined to space rafters greater than 650 c to c.


Answers
Answers ceilings are unlined to space rafters greater than 650 c to c.


Alternative set out
Alternative Set Out ceilings are unlined to space rafters greater than 650 c to c.

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
Similar Triangles ceilings are unlined to space rafters greater than 650 c to c.

If all angles are the same the triangles are similar

All sides are increased by same magnitude


Similar triangles1
Similar Triangles ceilings are unlined to space rafters greater than 650 c to c.


Basic steel square demo
Basic Steel Square Demo ceilings are unlined to space rafters greater than 650 c to c.

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
Graded Batten Roof ceilings are unlined to space rafters greater than 650 c to c.

  • Where direct fix ceiling is required to be level on flat roof

  • Fall is achieved with Battens


Constructing a skillion roof
Constructing a Skillion Roof ceilings are unlined to space rafters greater than 650 c to c.

Place End Rafters, allowing for soldier trims


Place Rafters at maximum 600 centres (580) ceilings are unlined to space rafters greater than 650 c to c.

Provide Solid Blocking at 1800 centers max


Install Soldier Trims ceilings are unlined to space rafters greater than 650 c to c.


Cut Overhangs & Install Verge Trims ceilings are unlined to space rafters greater than 650 c to c.


Install Wall Blocking ceilings are unlined to space rafters greater than 650 c to c.


Install Fascia ceilings are unlined to space rafters greater than 650 c to c.


Kliplock
Kliplock ceilings are unlined to space rafters greater than 650 c to c.

Minimum Pitch 1⁰


Trimdeck
Trimdeck ceilings are unlined to space rafters greater than 650 c to c.

Minimum Pitch 2⁰


Custom orb generally known as corrugated iron
Custom Orb ceilings are unlined to space rafters greater than 650 c to c. Generally Known as Corrugated Iron

Minimum Pitch 5⁰

Not Suitable For Flat Roofs


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