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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
Flush Gable with Raked Eaves
Roof Extends to Form eave
Ridge Extends to Form Eave
Verge Trimmers to Support Gable Rafter
Second Rafter to Support Verge Trims
Trimmers to Support Verge Trims and Roof Battens
Gable Stud supports 1. Second Rafter2. Brick Work or
Wall Lining
Top Plate may be extended to support Rafter
Boxed Gable
Purlin & Lintel Extended to Support Verge RafterMinimum Back span2 x OverhangDesign 3 x Overhang
Verge Rafter
Gable Studs & Sheeting
Base of Gable Lined & Level with U/S of Eaves
VergesIs the Junction of the Roof and the Barge/Verge Board
Verge Detail for Tiled Roof
Verge Detail for Tiled Roof
Principles of Roofing
1. Ridges are Level2. Rafters run at 903. Hips & Valleys bisect all internal & external Corners4. Roof members are set out along centrelines
Roofing Members
Common Rafter Ridge
Collar Tie
Purlin
StrutStrut
Ceiling Joist
Top Plate
Top Plate
Strutting Beam
Hanging Beam
Roof MembersCommon 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 Members
Common Rafter Ridge
Collar Tie
Purlin
StrutStrut
Ceiling Joist
Top Plate
Top Plate
Strutting Beam
Hanging Beam
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
Joining RidgeBoards
Roofing Members
Common Rafter Ridge
Collar Tie
Purlin
StrutStrut
Ceiling Joist
Top Plate
Top Plate
Strutting Beam
Hanging Beam
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 Members
Common Rafter Ridge
Collar Tie
Purlin
StrutStrut
Ceiling Joist
Top Plate
Top Plate
Strutting Beam
Hanging Beam
Struts
• Transfer Loads to Load Bearing Walls
Roofing Members
Common Rafter Ridge
Collar Tie
Purlin
StrutStrut
Ceiling Joist
Top Plate
Top Plate
Strutting Beam
Hanging Beam
Collar Ties
Common Rafter Principles
Birdsmouth Max 1/3 Depth of Rafter
Common Rafter PrinciplesSpan – From Birdsmouth to Birdsmouth
Half Span – From Birdsmouth to Centre
Common Rafter PrinciplesTrue Rise – Birdsmouth/Top of Rafter to Apex
NOTE – True Rise is not measured from TOP PLATE
Common Rafter PrinciplesIf Rise is taken from Top Plate to Apex pitch will be incorrect
Common Rafter Principles
Pitching Line x-y line
Common Rafter PrinciplesMeasured to edge of Ridge
Measured to centre of Ridge
Common Rafter Principles
True Length Centre Line Length
True Length is usually what we need
Determine Rafter LengthMathematically
Rafter 90 x 45Ridge 125 x 19
Determine Span = 2700mmDetermine Half Span = 2700/2
= 1350mmDetermine Rafter Run = 1350- Half Ridge Thickness = 19/2 = 9.5
Rafter Run = 1341.5
True Length Rafter = 1341.5 / Cos 25= 1480
OverhangPlan always from external wall
Determine Rafter LengthMathematically
Rafter 90 x 45Ridge 125 x 19
•Roofing calculations are always measured from Birdsmouth or pitching point
In this case Timber Famed Wall
O/H = 450 / cos 25 = 497mm
Rafter 90 x 45Ridge 125 x 19
In this case Brick Veneer Wall
O/H = 450 + 40 + 110 cos 25
= 662mm
Determine Rafter LengthMathematically
Total Rafter Length Timber Frame = 1480 + 497 = 1977mmBrick Veneer = 1480 + 662 = 2142mm
Rafter 90 x 45Ridge 125 x 19
Determine Rafter LengthGraphically
1. Draw Roof Full-size2. Measure members directly3. Avoid using scaled drawing4. Scale use only for angles
Determine Rafter LengthUsing Roofing Square
Use Calculator
1. Press Tan 25 – what does this give you2. Therefore for every 1 metre run there is
0.466m rise3. Using the principle of similar triangles
we half the size of the triangle
Use Calculator
1. Press Tan 25 – what does this give you2. Therefore for every 1 metre run there is
0.466m rise3. Using the principle of similar triangles
we half the size of the triangle
Use Calculator
1. Press Tan 25 – what does this give you2. Therefore for every 1 metre run there is
0.466m rise3. Using the principle of similar triangles
we half the size of the triangle
Using Similar Triangles1341/500 = 2.682 or
= 2 r 341
Using Similar Triangles1341/500 = 2.682 or
= 2 r 341
Select Start Point Allowing for O/H
Step out 2 full triangles
Intersection of Top of Rafter & Edge of Square
Using Similar Triangles1341/500 = 2.682 or
= 2 r 341
Select Start Point Allowing for O/H
Step out 2 full triangles
Step out 341 & use square to extend
Determine Roofing Anglesused in Gable Roofs
Plumb Cut
Foot Cut
Determining Angles with Roofing Square
When we set out rafter previously we determined plumb cut
Determining Angles with Roofing Square
Plumb CutFoot Cut
Determining Angles Mathematically
1. Extend Line 90⁰ From Rafter
Determining Angles Mathematically
1. Extend Line 90⁰ From Rafter2. Extend Plumb Line
Determining Angles Mathematically
1. Extend Line 90⁰ From Rafter2. Extend Plumb Line3. Angle Formed is same as
roof pitch
Determining Angles Mathematically
1. Extend Line 90⁰ From Rafter2. Extend Plumb Line3. Angle Formed is same as
roof pitch4. Offset = Tan (pitch) x width
Determining Angles Mathematically
1. Extend Line 90⁰ From Rafter2. Extend Plumb Line3. Angle Formed is same as
roof pitch4. Offset = Tan (25⁰) x 90
= 42
Complete Q5 in Workbook
Determine Roof AnglesGraphically
Plan – View
We can only see rafter run
Determine Roof AnglesGraphically
Extend Top Plate & Ridge
Determine Roof AnglesGraphically
Extend Top Plate & Ridge
Mark Rise
Determine Roof AnglesGraphically
Extend Top Plate & Ridge
Mark Rise
Draw Hypotenuse
Plumb Cut
Foot Cut
