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Gable Roof BCGCA3007B

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Gable Roof Flush with no eaves Flush with raked eaves Boxed

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**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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**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

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**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

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**Verges Is the Junction of the Roof and the Barge/Verge Board**

Verge Detail for Tiled Roof

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**Verge Detail for Tiled Roof**

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**Principles of Roofing Ridges are Level Rafters run at 90**

Hips & Valleys bisect all internal & external Corners Roof members are set out along centerlines

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**Roofing Members Ridge Common Rafter Collar Tie Top Plate Hanging Beam**

Purlin Top Plate Strutting Beam Strut Ceiling Joist Strut

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**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)

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**Roofing Members Ridge Common Rafter Collar Tie Top Plate Hanging Beam**

Purlin Top Plate Strutting Beam Strut Ceiling Joist Strut

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**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

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Joining Ridge Boards

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**Roofing Members Ridge Common Rafter Collar Tie Top Plate Hanging Beam**

Purlin Top Plate Strutting Beam Strut Ceiling Joist Strut

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**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

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**Roofing Members Ridge Common Rafter Collar Tie Top Plate Hanging Beam**

Purlin Top Plate Strutting Beam Strut Ceiling Joist Strut

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Struts Transfer Loads to Load Bearing Walls

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**Roofing Members Ridge Common Rafter Collar Tie Top Plate Hanging Beam**

Purlin Top Plate Strutting Beam Strut Ceiling Joist Strut

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Collar Ties

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**Common Rafter Principles**

Birdsmouth Max 1/3 Depth of Rafter

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**Common Rafter Principles**

Span – From Birdsmouth to Birdsmouth Half Span – From Birdsmouth to Centre

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**Common Rafter Principles**

True 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

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**A Closer Look Top Of Rafter Birds Mouth Top Plate Ceiling Joist**

NOTE – True Rise is not measured from TOP PLATE

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**Common Rafter Principles**

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

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**Common Rafter Principles**

Pitching Line x-y line

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**Common Rafter Principles**

Measured to edge of Ridge Measured to centre of Ridge

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**Common Rafter Principles**

Centre Line Length True Length True Length is usually what we need

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**Determine Rafter Length Mathematically**

Determine Span = 2700mm Determine Half Span = 2700/2 = 1350mm Determine Rafter Run = 1350- Half Ridge Thickness = 19/2 = 9.5 Rafter Run = True Length Rafter = / Cos 25 = 1480 Rafter 90 x 45 Ridge 125 x 19

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**Overhang Plan always from external wall**

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**Determine Rafter Length Mathematically**

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

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**Determine Rafter Length Mathematically**

In this case Brick Veneer Wall O/H = cos 25 = 662mm Total Rafter Length Timber Frame = = 1977mm Brick Veneer = = 2142mm Rafter 90 x 45 Ridge 125 x 19

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**Determine Rafter Length Graphically**

Draw Roof Full-size Measure members directly Avoid using scaled drawing Scale use only for angles Rafter 90 x 45 Ridge 125 x 19

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**Determine Rafter Length Using 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

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**Press Tan 25 – what does this give you **

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

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**Press Tan 25 – what does this give you **

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

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**Using Similar Triangles**

1341/500 = or = 2 r 341

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**Using Similar Triangles 1341/500 = 2.682 or = 2 r 341**

Step out 2 full triangles Select Start Point Allowing for O/H

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**Intersection of Top of Rafter & Edge of Square**

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**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

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**Determine Roofing Angles used in Gable Roofs**

Plumb Cut Foot Cut

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**Determining Angles with Roofing Square**

When we set out rafter previously we determined plumb cut

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**Determining Angles with Roofing Square**

Plumb Cut Foot Cut

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**Determining Angles Mathematically**

Extend Line 90⁰ From Rafter

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**Determining Angles Mathematically**

Extend Line 90⁰ From Rafter Extend Plumb Line

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**Determining Angles Mathematically**

Extend Line 90⁰ From Rafter Extend Plumb Line Angle Formed is same as roof pitch

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**Determining Angles Mathematically**

Extend Line 90⁰ From Rafter Extend Plumb Line Angle Formed is same as roof pitch Offset = Tan (pitch) x width

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**Determining Angles Mathematically**

Extend Line 90⁰ From Rafter Extend Plumb Line Angle Formed is same as roof pitch Offset = Tan (25⁰) x = 42

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**Determining Angles Mathematically**

Next we can Determine our Birdsmouth Width across plumb cut = 90/ cos 25 = 99 Therefore max Birdsmouth = 33 Distance from top plate to top of Rafter = 66

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Complete Q5 in Workbook

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**Determine Roof Angles Graphically**

Plan – View We can only see rafter run

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**Determine Roof Angles Graphically**

Extend Top Plate & Ridge

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**Determine Roof Angles Graphically**

Extend Top Plate & Ridge Mark Rise

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**Determine Roof Angles Graphically**

Plumb Cut Extend Top Plate & Ridge Mark Rise Draw Hypotenuse Foot Cut

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**Steps In Construction Gable Roof**

Physically Confirm Span & Plates are Parallel Calculate True Rafter, Rise & Plumbcuts Mark out ceiling joists, rafters & ridge Install Ceiling Joists Cut Pattern Rafter & test to confirm Cut required rafters & install

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**Estimating Gable Roof - Rafter From Previous Ceiling Estimate**

Pitch = 25⁰ Determine No of Ceiling Joists 12 250/ 600 = = = Therefore 22 set of Rafters = Verge = 48

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**Determine Rafter Length**

Span = 6900

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**Determine Rafter Length**

Span = 6900 Half Span = 3450

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**Determine Rafter Length**

Span = 6900 Half Span = 3450 Run = 3450 – 9.5 (Half Ridge) =

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**Determine Rafter Length**

Span = 6900 Half Span = 3450 Run = 3450 – 9.5 = True Length = / cos 24 =3766

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**Determine Rafter Length**

Span = 6900 Half Span = 3450 Run = 3450 – 9.5 = True Length = / cos 24 =3766 Overhang = 450/cos 24 = 493

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**Determine Rafter Length**

Span = 6900 Half Span = 3450 Run = 3450 – 9.5 = True Length = / cos 24 =3766 Overhang = 450/cos 24 = 493 Total Rafter = 4259

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Estimating Sheet

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**Estimating Gable Roof - Purlin**

Pitch = 24⁰ Overhang 450 Rafter 90 x 45 F7 600 c to c Tiled Roof Ridge 140 x 19 Purlin 90 x 70 F7 Purlin Run full length of Roof Do we need purlins

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Span Required = 3766 Max Span 2600 3766/2600 = 1.4 Therefore 1 row required each side In First Instance we check single span Max Span = 1900

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**Estimating Gable Roof -Purlin**

Pitch = 24⁰ Overhang 450 Rafter 90 x 45 F7 600 c to c Tiled Roof with Flush Gable & Raking Eaves Ridge 140 x 19 Purlin 90 x 70 F7 Purlin Run full length of Roof Do we need purlins Purlins Run Full Length x 150 (Joins) =

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Estimating Sheet

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**Estimating Gable Roof - Ridge**

Pitch = 24⁰ Overhang 450 Rafter 90 x 45 F7 600 c to c Tiled Roof with Flush Gable & Raking Eaves Ridge 140 x 19 Purlin 90 x 70 F7 Ridge Runs Full Length x 450 (O/H) x 300 (allow for joins) =14000mm Note – For Flush eaves there is no O/H ridge = 12500 Boxed eaves will require O/H ridge = 13400mm

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Estimating Sheet

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**Estimating Gable Roof - Struts**

Pitch = 24⁰ Overhang 450 Rafter 90 x 45 F7 600 c to c Tiled Roof with Flush Gable & Raking Eaves Ridge 140 x 19 Purlin 90 x 70 F7 Span 2700 Struts are Difficult to Estimate Develop a Best Guest Method Determine No Required 12500/2700 = 4.6 = 5 = 6 Each Side

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**Estimating Gable Roof - Struts**

Pitch = 24⁰ Overhang 450 Rafter 90 x 45 F7 600 c to c Tiled Roof with Flush Gable & Raking Eaves Ridge 140 x 19 Purlin 90 x 70 F7 Span 2700 Struts are Difficult to Estimate Develop a Best Guest Method Half Rise x √2 x √2 Tan 24⁰ x 3441 x 2 = 3064 Determine No Required 12500/2700 = 4.6 = 5 = 6 Each Side

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Estimating Sheet

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**Estimating Gable Roof – Collar Ties**

Pitch = 24⁰ Overhang 450 Rafter 90 x 45 F7 600 c to c Tiled Roof with Flush Gable & Raking Eaves Ridge 140 x 19 Purlin 90 x 70 F7 Span 2700 Collar Ties 90 x 35 Collar Ties on Every 2nd Rafter On top of Purlins 22/2 = HALF SPAN 3450

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Estimating Sheet

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**Estimating Gable Roof – Verge Trims**

Pitch = 24⁰ Overhang 450 Rafter 90 x 45 F7 600 c to c Tiled Roof with Flush Gable & Raking Eaves Ridge 140 x 19 Purlin 90 x 70 F7 Span 2700 Collar Ties 90 x 35 True Length of Rafter

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Rafter True length / 600 = 6.28 = 7 (Ridge Closes) = 33.6 Say 33.9

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Estimating Sheet

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**One Row of Purlin Each Side**

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Roofs By Denis Gifford.

Roofs By Denis Gifford.

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