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Gable Roof. BCGCA3007B. Gable Roof. Flush with no eaves Flush with raked eaves Boxed. Flush Gable (No Eaves). Rafter finishes in line with end wall Barge fixed to outside wall No Overhang. Studwork to take sheeting or support brickwork Not required to support roof.

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gable roof

Gable Roof

BCGCA3007B

gable roof1
Gable Roof
  • Flush with no eaves
  • Flush with raked eaves
  • Boxed
flush gable no eaves
Flush Gable (No Eaves)
  • Rafter finishes in line with end wall
  • Barge fixed to outside wall
  • No Overhang

Studwork to take sheeting or support brickwork

Not required to support roof

flush gable with raked eaves
Flush Gable with Raked Eaves

Ridge Extends to Form Eave

Verge Trimmers to Support Gable Rafter

Trimmers to Support Verge Trims and Roof Battens

Gable Stud supports

Second Rafter

Brick Work or Wall Lining

Second Rafter to Support Verge Trims

Roof Extends to Form eave

Top Plate may be extended to support Rafter

boxed gable
Boxed Gable

Verge Rafter

Gable Studs & Sheeting

Purlin & Lintel Extended to Support Verge Rafter

Minimum Back span

2 x Overhang

Design 3 x Overhang

Base of Gable Lined & Level with U/S of Eaves

principles of roofing
Principles of Roofing

Ridges are Level

Rafters run at 90

Hips & Valleys bisect all internal & external Corners

Roof members are set out along centrelines

roofing members
Roofing Members

Ridge

Common Rafter

Collar Tie

Top Plate

Hanging Beam

Purlin

Top Plate

Strutting Beam

Strut

Ceiling Joist

Strut

roof members
Roof Members

Common Rafter –

  • Main Sloping Roof Member
  • Spacing 450mm or 600mm for Tiled Roofs
  • 900mm for tiled roofs
  • Supports Roof Battens which in turn support roof coverings
  • Must be in single lengths or joined over supports
  • Fixings 2 x 75mm Skew & 2 x 75mm into Ceiling Joist (if joist is > 38, 90mm Nails)
roofing members1
Roofing Members

Ridge

Common Rafter

Collar Tie

Top Plate

Hanging Beam

Purlin

Top Plate

Strutting Beam

Strut

Ceiling Joist

Strut

ridge
Ridge
  • Highest Part of the Roof
  • Will run full length of Gable Roof
  • Runs Parallel to TOP PLATE
  • Fixes Rafters at Top of Roof
  • Rafters are nailed either side and not offset by more than 1 thickness
  • In Uncoupled Roof, they act as beams
  • Nailed to Rafters with 2 x 75mm Nails
roofing members2
Roofing Members

Ridge

Common Rafter

Collar Tie

Top Plate

Hanging Beam

Purlin

Top Plate

Strutting Beam

Strut

Ceiling Joist

Strut

purlin
Purlin
  • Also known as Underpurlin
  • Fixed to Underside of RAFTER
  • Runs parallel to ridge and wall plates
  • Reduce span of RAFTER
  • Will run full length of Gable Roof
roofing members3
Roofing Members

Ridge

Common Rafter

Collar Tie

Top Plate

Hanging Beam

Purlin

Top Plate

Strutting Beam

Strut

Ceiling Joist

Strut

struts
Struts
  • Transfer Loads to Load Bearing Walls
roofing members4
Roofing Members

Ridge

Common Rafter

Collar Tie

Top Plate

Hanging Beam

Purlin

Top Plate

Strutting Beam

Strut

Ceiling Joist

Strut

common rafter principles
Common Rafter Principles

Birdsmouth Max 1/3 Depth of Rafter

common rafter principles1
Common Rafter Principles

Span – From Birdsmouth to Birdsmouth

Half Span – From Birdsmouth to Centre

common rafter principles2
Common Rafter Principles

True Rise – Birdsmouth/Top of Rafter to Apex

NOTE – True Rise is not measured from TOP PLATE

common rafter principles3
Common Rafter Principles

If Rise is taken from Top Plate to Apex pitch will be incorrect

common rafter principles4
Common Rafter Principles

Pitching Line x-y line

common rafter principles5
Common Rafter Principles

Measured to edge of Ridge

Measured to centre of Ridge

common rafter principles6
Common Rafter Principles

Centre Line Length

True Length

True Length is usually what we need

determine rafter length mathematically
Determine Rafter LengthMathematically

Determine Span = 2700mm

Determine Half Span = 2700/2

= 1350mm

Determine Rafter Run = 1350-

Half Ridge Thickness = 19/2 = 9.5

Rafter Run = 1341.5

True Length Rafter = 1341.5 / Cos 25

= 1480

Rafter 90 x 45

Ridge 125 x 19

determine rafter length mathematically1
Determine Rafter LengthMathematically

In this case Timber Famed Wall

O/H = 450 / cos 25

= 497mm

  • Roofing calculations are always measured from Birdsmouth or pitching point

Rafter 90 x 45

Ridge 125 x 19

determine rafter length mathematically2
Determine Rafter LengthMathematically

In this case Brick Veneer Wall

O/H = 450 + 40 + 110

cos 25

= 662mm

Total Rafter Length

Timber Frame = 1480 + 497 = 1977mm

Brick Veneer = 1480 + 662 = 2142mm

Rafter 90 x 45

Ridge 125 x 19

determine rafter length graphically
Determine Rafter LengthGraphically

Draw Roof Full-size

Measure members directly

Avoid using scaled drawing

Scale use only for angles

Rafter 90 x 45

Ridge 125 x 19

determine rafter length using roofing square
Determine Rafter LengthUsing Roofing Square

Use Calculator

Press Tan 25 – what does this give you

Therefore for every 1 metre run there is 0.466m rise

Using the principle of similar triangles we half the size of the triangle

slide38

Use Calculator

Press Tan 25 – what does this give you

Therefore for every 1 metre run there is 0.466m rise

Using the principle of similar triangles we half the size of the triangle

slide39

Use Calculator

Press Tan 25 – what does this give you

Therefore for every 1 metre run there is 0.466m rise

Using the principle of similar triangles we half the size of the triangle

slide40

Using Similar Triangles

1341/500 = 2.682 or

= 2 r 341

slide41

Using Similar Triangles

1341/500 = 2.682 or

= 2 r 341

Step out 2 full triangles

Select Start Point Allowing for O/H

slide43

Using Similar Triangles

1341/500 = 2.682 or

= 2 r 341

Step out 341 & use square to extend

Step out 2 full triangles

Select Start Point Allowing for O/H

slide45

Determining Angles with Roofing Square

When we set out rafter previously we determined plumb cut

slide47

Determining Angles Mathematically

Extend Line 90⁰ From Rafter

slide48

Determining Angles Mathematically

Extend Line 90⁰ From Rafter

Extend Plumb Line

slide49

Determining Angles Mathematically

Extend Line 90⁰ From Rafter

Extend Plumb Line

Angle Formed is same as roof pitch

slide50

Determining Angles Mathematically

Extend Line 90⁰ From Rafter

Extend Plumb Line

Angle Formed is same as roof pitch

Offset = Tan (pitch) x width

slide51

Determining Angles Mathematically

Extend Line 90⁰ From Rafter

Extend Plumb Line

Angle Formed is same as roof pitch

Offset = Tan (25⁰) x 90 = 42

determine roof angles graphically
Determine Roof AnglesGraphically

Plan – View

We can only see rafter run

determine roof angles graphically1
Determine Roof AnglesGraphically

Extend Top Plate & Ridge

determine roof angles graphically2
Determine Roof AnglesGraphically

Extend Top Plate & Ridge

Mark Rise

determine roof angles graphically3
Determine Roof AnglesGraphically

Plumb Cut

Extend Top Plate & Ridge

Mark Rise

Draw Hypotenuse

Foot Cut