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 centerlines

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 Ridge Boards

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 –From Horizontal line that passes thru the Intersection of Birdsmouth Plumb Line &Top of Rafter To : vertically plumb up to the Apex

NOTE – True Rise is not measured from TOP PLATE

A Closer Look

NOTE – True Rise is not measured from TOP PLATE

Top Of Rafter

Ceiling JoistTop Plate

Birds Mouth

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

Determining Angles MathematicallyNext we can Determine our Birdsmouth1. Width across plumb cut = 90/ cos 252. = 993. Therefore max Birdsmouth = 334. Distance from top plate to top of

Rafter = 66

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

Steps In ConstructionGable Roof

1. Physically Confirm Span & Plates are Parallel2. Calculate True Rafter, Rise & Plumbcuts3. Mark out ceiling joists, rafters & ridge4. Install Ceiling Joists5. Cut Pattern Rafter & test to confirm6. Cut required rafters & install

Estimating Gable Roof - RafterFrom Previous Ceiling Estimate

Determine No of Ceiling Joists 12 250/ 600 = 20.4167 = 21 + 1 = 22 @6900

Pitch = 25⁰

Therefore 22 set of Rafters = 44 + 4 Verge= 48

Determine Rafter LengthSpan = 6900

Determine Rafter LengthSpan = 6900Half Span = 3450

Determine Rafter LengthSpan = 6900Half Span = 3450Run = 3450 – 9.5 (Half Ridge)

= 3340.5

Determine Rafter LengthSpan = 6900Half Span = 3450Run = 3450 – 9.5

= 3440.5True Length = 3440.5 / cos 24

=3766

Determine Rafter LengthSpan = 6900Half Span = 3450Run = 3450 – 9.5

= 3440.5True Length = 3440.5 / cos 24

=3766Overhang = 450/cos 24 = 493

Determine Rafter LengthSpan = 6900Half Span = 3450Run = 3450 – 9.5

= 3440.5True Length = 3440.5 / cos 24

=3766Overhang = 450/cos 24 = 493Total Rafter = 4259

Estimating Sheet

No. LengthRafters 90 x 45 Radiata 48 4.259 4.500 216.000 2.30$ 496.80$

Total Linear Rate / lm Cost Order

Item Section Size Material Linear

Estimating Gable Roof - PurlinPitch = 24⁰

Overhang 450

Rafter 90 x 45 F7600 c to cTiled Roof

Ridge 140 x 19Purlin 90 x 70 F7

PurlinRun full length of RoofDo we need purlins

In First Instance we check single span Max Span = 1900

Span Required = 3766Max Span 26003766/2600 = 1.4Therefore 1 row required each side

Estimating Gable Roof -PurlinPitch = 24⁰

Overhang 450

Rafter 90 x 45 F7600 c to c

Tiled Roof with Flush Gable & Raking Eaves

Ridge 140 x 19Purlin 90 x 70 F7

PurlinRun full length of RoofDo we need purlins

Purlins Run Full Length2 @ 12.500 + 2 x 150 (Joins)

= 12.800

Estimating Sheet

No. LengthRafters 90 x 45 Radiata 48 4.259 4.500 216.000 2.30$ 496.80$ Purlins 90 x 70 Radiata 2 12.800 12.900 25.800 3.80$ 98.04$

Total Linear Rate / lm Cost Order

Item Section Size Material Linear

Estimating Gable Roof - RidgePitch = 24⁰

Overhang 450

Rafter 90 x 45 F7600 c to c

Tiled Roof with Flush Gable & Raking Eaves

Ridge 140 x 19Purlin 90 x 70 F7

Ridge Runs Full Length12.500 +2 x 450 (O/H) 13400 + 2 x 300 (allow for joins)

=14000mm

Note – For Flush eaves there is no O/H ridge = 12500Boxed eaves will require O/H ridge = 13400mm

Estimating Sheet

No. LengthRafters 90 x 45 Radiata 48 4.259 4.500 216.000 2.30$ 496.80$ Purlins 90 x 70 Radiata 2 12.800 12.900 25.800 3.80$ 98.04$ Ridge 140 x 19 Radiata 1 14.000 14.100 14.100 3.50$ 49.35$

Total Linear Rate / lm Cost Order

Item Section Size Material Linear

Estimating Gable Roof - StrutsPitch = 24⁰

Overhang 450

Rafter 90 x 45 F7600 c to c

Tiled Roof with Flush Gable & Raking Eaves

Ridge 140 x 19

Purlin 90 x 70 F7Span 2700

Struts are Difficult to EstimateDevelop a Best Guest Method

Determine No Required12500/2700 = 4.6 = 5 = 6 Each Side

Estimating Gable Roof - StrutsPitch = 24⁰

Overhang 450

Rafter 90 x 45 F7600 c to c

Tiled Roof with Flush Gable & Raking Eaves

Ridge 140 x 19

Purlin 90 x 70 F7Span 2700

Struts are Difficult to EstimateDevelop a Best Guest Method

Half Rise x √2 x √2Tan 24⁰ x 3441 x 2

= 3064Determine No Required12500/2700 = 4.6 = 5 = 6 Each Side

Estimating Sheet

No. LengthRafters 90 x 45 Radiata 44 4.259 4.500 198.000 2.30$ 455.40$ Purlins 90 x 70 Radiata 2 12.800 12.900 25.800 3.80$ 98.04$ Ridge 140 x 19 Radiata 1 14.000 14.100 14.100 3.50$ 49.35$ Struts 90 x 70 Radiata 6 3.064 3.300 19.800 3.80$ 75.24$

Total Linear Rate / lm Cost Order

Item Section Size Material Linear

Estimating Gable Roof – Collar TiesPitch = 24⁰

Overhang 450

Rafter 90 x 45 F7600 c to c

Tiled Roof with Flush Gable & Raking Eaves

Ridge 140 x 19

Purlin 90 x 70 F7Span 2700

Collar Ties 90 x 35Collar Ties on Every 2nd RafterOn top of Purlins22/2 = 11 @ HALF SPAN11 @ 3450

Estimating Sheet

No. LengthRafters 90 x 45 Radiata 44 4.259 4.500 198.000 2.30$ 455.40$ Purlins 90 x 70 Radiata 2 12.800 12.900 25.800 3.80$ 98.04$ Ridge 140 x 19 Radiata 1 14.000 14.100 14.100 3.50$ 49.35$ Struts 90 x 70 Radiata 6 3.064 3.300 19.800 3.80$ 75.24$

Collar Ties 90 x 35 Radiata 11 3.450 3.600 39.600 2.00$ 79.20$

Total Linear Rate / lm Cost Order

Item Section Size Material Linear

Estimating Gable Roof – Verge Trims

Pitch = 24⁰

Overhang 450

Rafter 90 x 45 F7600 c to c

Tiled Roof with Flush Gable & Raking Eaves

Ridge 140 x 19

Purlin 90 x 70 F7Span 2700

Collar Ties 90 x 35True Length of Rafter

Rafter True length / 600= 6.28 = 7 (Ridge Closes)

28 @ 1200 = 33.6Say 33.9

Estimating Sheet

No. LengthRafters 90 x 45 Radiata 44 4.259 4.500 198.000 2.30$ 455.40$ Purlins 90 x 70 Radiata 2 12.800 12.900 25.800 3.80$ 98.04$ Ridge 140 x 19 Radiata 1 14.000 14.100 14.100 3.50$ 49.35$ Struts 90 x 70 Radiata 6 3.064 3.300 19.800 3.80$ 75.24$

Collar Ties 90 x 35 Radiata 11 3.450 3.600 39.600 2.00$ 79.20$ Verge Trims 90 x 45 Radiata 1 33.900 33.900 33.900 2.30$ 77.97$

Total 835.20$

Total Linear Rate / lm Cost Order

Item Section Size Material Linear

One Row of Purlin Each Side