Gable Roof BCGCA3007B.

Name: Gable Roof BCGCA3007B.
Uploaded: 2017-07-13T15:24:58+00:00
Duration: PTM57S20
Channel: Makayla Grimmer
Description: Gable Roof BCGCA3007B.

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
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 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

Verges Is the Junction of the Roof and the Barge/Verge Board
Verge Detail for Tiled Roof

Verge Detail for Sheet Metal Roof

Principles of Roofing Ridges are Level
Rafters run at 90 to wall plates Hips & Valleys bisect all internal & external Corners Roof members are set out along centerlines

Roofing Members Ridge Common Rafter Collar Tie Top Plate Hanging Beam
Purlin Top Plate Strutting Beam Strut Ceiling Joist Strut

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 (Nominal) 2 x 75mm Skew & 2 x 75mm into Ceiling Joist (if joist is > 38, 90mm Nails)

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

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

Struts Transfer Loads From Purlins to Load Bearing Walls

Also Known as Barrap Straps

Collar Ties

Gable Roof Common Rafter

Common Rafter Main Roofing Member Calculated same method as Gable
Spaced Usually at 450mm to 600mm for Tiled Roofs & 600mm to 900mm for Sheet Roof Cut using a Pattern Rafter

Gable Roof Common Rafter Top Plate

Top Plate Top Part of the Wall Frame
Takes structural load from Roof and Transfers it to the wall studs Size must be determined from span tables

Pitching Line Pitching Line

Pitching Line Pitching Line Starts at top corner of Top Plate

Pitching Line Pitching Line Starts at top corner of Top Plate
Pitching line Runs Parallel to top of Rafter

Pitching line Runs Parallel to top of Rafter This establishes the Pitch of the Roof

If the pitching line went from top plate to top of roof the pitch is not correct or relevant. As you will see later it would make our calculations far harder

Common Rafter Principles
Span – From Birdsmouth to Birdsmouth Half Span – From Birdsmouth to Centre

Rise – Vertical height from top plate to intersections of pitching lines at Apex Rise is NOT measured to top of Rafter

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

Measured to edge of Ridge Measured to centre of Ridge

Confirmation of Learning
Mark on Drawing in Workbook where, Centreline Length is measured to

Centreline Length Centre Line Length

Mark on Drawing in Workbook where, True Length is measured to Centre Line Length

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

Confirmation Of Learning
Mark on Drawing in Workbook where, Rafter is measured from at Base

Measurement of Rafter Mark on Drawing in Workbook where,
Rafter is measured from at Base Rafter is measured from this point

Mark on Drawing in Workbook where, The Rafter Length is measured

The Rafter Length is measured The Rafter Length is measure along the pitching line

The Rafter Length is measured You may also measure on any line that is parallel to the pitching line so long as it is between Plumb lines that pass thru the required points.

Determine Rafter Length Mathematically
For every roof you must solve the 1m triangle based on the roof pitch Rafter 90 x 45 Ridge 125 x 19

The “1 Metre Triangle”

Step 1 - Solve 1m Triangle Rafter Length per 1 metre of Plan length
Rise per 1 metre of Plan Length 25° This is the a triangle based on the roof pitch Plan Length of 1 metre

Step 1 - Solve 1m Triangle Rafter Length per 1 metre of Plan length
Rise per 1 metre of Plan Length 25° This is always no matter what the Roof Pitch is Plan Length of 1 metre

Step 1 - Solve 1m Triangle These dimension will always change and are dependant on the Roof Pitch. These figures will need to be determined by you. Rafter Length per 1 metre of Plan length Rise per 1 metre of Plan Length 25° Plan Length of 1 metre

Step 1 - Solve 1m Triangle Solve all Unknown Sides of the a triangle based on the roof pitch Unknown Unknown 25° 1.000 Horizontal Travel = “Plan Length”

Step 1 - Solve 1m Triangle Solve all Unknown Sides of the a triangle based on the roof pitch Unknown 0.466 Rise = Plan Length x Tan (Pitch)° = x Tan 25° = 0.466 25° 1.000 Horizontal Travel = “Plan Length”

Step 1 - Solve 1m Triangle Rafter Length / m = Plan Length ÷ Cos (Pitch)° = ÷ Cos 25° = ÷ = 1.103 Solve all Unknown Sides of the a triangle based on the roof pitch 1.103 0.466 Rise = 1 x Tan 25° = 0.466 25° 1.000 Horizontal Travel = “Plan Length”

Step 1 - Solved 1m Triangle
For any roof of 25° the Rafter Length per 1 m of Plan Length For any roof of 25° the Rise per 1 m of Plan Length 1.103 0.466 25° 1.000 Horizontal Travel = “Plan Length”

Determine the following 1 metre triangles 16° 20° 45° 30°

Determine the following 1 metre triangles 1.064 1.040 0.287 0.364 16° 20° 1.000 1.414 1.000 1.155 0.577 45° 30° 1.000 1.000

Determine Centreline Length
Ridge Centreline Length is to the Centre of the Roof ½ Span

Definition – Plan Length
“Plan Length” is the Horizontal (Level) Distance a Roofing Member Travels A Rafter is 3310 and is pitched at 25° 3310 25° Plan Length

Plan Length is the Horizontal (Level) Distance a Roofing Member Travels 3310 The Horizontal Distance that the Rafter Travels is its “PLAN LENGTH In this case is 3000 25° 3000

Plan Length is the Horizontal (Level) Distance a Roofing Member Travels 3310 It is important when determining any Rafter Hip Creeper Valley etc., To first determine its plan length 25° 3000

What is the “Plan Length” of this Rafter? 2750 1887 2000

What is the “Plan Length” of this Rafter? 2750 1887 2000 This is the plan length

Centreline Length What is the plan length we need to use to determine the Centreline Length of the common rafter below ? Rafter 90 x 45 Ridge 125 x 19

Step 2 – Determine Plan Length Centreline Length
Determine how far the rafter travels HORIZONTALLY PLAN LENGTH 1.103 0.466 25° 1350(1/2 Span) Plan Length 1 “Plan Length” = ½ Span = 1350

Step 2 – Determine Plan Length Centreline Length
Determine how far the rafter travels HORIZONTALLY PLAN LENGTH 1.103 0.466 25° 1350(1/2 Span) Plan Length 1 For any Rafter (or Hip) you must first determine the Horizontal Travel i.e. PLAN LENGTH “Plan Length” = ½ Span = 1350 Plan Length= 1350

Principle Of Similar Triangles
If all 3 angles of 2 triangles are equal There will be the same proportional difference between the corresponding sides of the triangle 65° 2.206 2x 1.862 1.103 65° 0.466 25° 25° 1 2 The right hand triangle is 2x the size of the “1 meter triangle”

Understanding the Principle Of Similar Triangles
65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 This is our “1 meter” triangle

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 This is the TARGET triangle formed by the rafter

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 The first step is to determine proportional ratio between the triangles

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 The first step is to determine proportional ratio between the triangles To determine this we ALWAYS determine using the PLAN lengths

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 Target Triangle 1 Metre Triangle The first step is to determine proportional ratio between the triangles To determine this we ALWAYS determine using the PLAN lengths Ratio = Plan length of “TARGET” triangle ÷ Plan length “1 metre” triangle

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 The first step is to determine proportional ratio between the triangles To determine this we ALWAYS determine using the PLAN lengths Ratio = Plan length of TARGET triangle ÷ Plan length “1 meter” triangle Ratio = 2 ÷ 1 Ratio = 2

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 The first step is to determine proportional ratio between the triangles To determine this we ALWAYS determine using the PLAN lengths Ratio = Plan length of TARGET triangle ÷ Plan length “1 meter” triangle Ratio = 2 ÷ 1 Ratio = 2 We will call this the triangle multiplier

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 The first step is to determine proportional ratio between the triangles To determine this we ALWAYS determine using the PLAN lengths Ratio = Plan length of TARGET triangle ÷ Plan length “1 meter” triangle Ratio = 2 ÷ 1 Ratio = 2 For the Common Rafter as we use the “1 meter” triangle, the Triangle Multiplier will always = Plan length of the Target triangle

Step 3 – Determine Rafter Length Centreline Length
1489 1.103 0.466 25° 1350 ½ Span Plan Length 1 Rafter Length = Plan Length x Rafter Length per metre (RL/m) Rafter Length = x 1.103 Rafter Length = 1489

Step 4 – Determine Rise (If Required) Centreline Length
1489 629 1.103 0.466 25° 1350 (1/2 Span) Plan Length 1 Total Rise = Horizontal Travel x Rise per metre Total Rise = 1350 x 0.466 Total Rise = 629

True Length What is the plan length we need to use to determine the True Length of the common rafter below ? Rafter 90 x 45 Ridge 125 x 19

Determine Centreline Length
Ridge 125 x19 True Length is to the Side of the Ridge ½ Span – ½ Ridge Thickness

Step 2 – Determine Plan Length True Length
Ridge 125 x 19 Determine how far the rafter travels HORIZONTALLY PLAN LENGTH 1.103 0.466 25° 1341 Plan Length 1 “Plan Length” = ½ Span – ½ Ridge Thickness = 1350 – 9.5 = 1341

Step 2 – Determine Plan Length Trur Length
Ridge 125 x 19 Determine how far the rafter travels HORIZONTALLY PLAN LENGTH 1.103 0.466 25° 1350(1/2 Span) Plan Length 1 For any Rafter (or Hip) you must first determine the Horizontal Travel i.e. PLAN LENGTH “Plan Length” = 1341

Principle Of Similar Triangles
If all 3 angles of 2 triangles are equal There will be the same proportional difference between the corresponding sides of the triangle 65° 2.206 2x 1.862 1.103 65° 0.466 25° 25° 1 2 The right hand triangle is 2x the size of the “1 meter triangle”

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 This is our “1 meter” triangle

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 This is the TARGET triangle formed by the rafter

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 The first step is to determine proportional ratio between the triangles

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 The first step is to determine proportional ratio between the triangles To determine this we ALWAYS determine using the PLAN lengths

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 Target Triangle 1 Metre Triangle The first step is to determine proportional ratio between the triangles To determine this we ALWAYS determine using the PLAN lengths Ratio = Plan length of “TARGET” triangle ÷ Plan length “1 metre” triangle

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 The first step is to determine proportional ratio between the triangles To determine this we ALWAYS determine using the PLAN lengths Ratio = Plan length of TARGET triangle ÷ Plan length “1 meter” triangle Ratio = 2 ÷ 1 Ratio = 2

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 The first step is to determine proportional ratio between the triangles To determine this we ALWAYS determine using the PLAN lengths Ratio = Plan length of TARGET triangle ÷ Plan length “1 meter” triangle Ratio = 2 ÷ 1 Ratio = 2 We will call this the triangle multiplier

65° 2.206 1.862 1.103 65° 0.466 25° 25° 1 2 The first step is to determine proportional ratio between the triangles To determine this we ALWAYS determine using the PLAN lengths Ratio = Plan length of TARGET triangle ÷ Plan length “1 meter” triangle Ratio = 2 ÷ 1 Ratio = 2 For the Common Rafter as we use the “1 meter” triangle, the Triangle Multiplier will always = Plan length of the Target triangle

Step 3 – Determine Rafter Length True Length
1479 1.103 0.466 25° 1341 Plan Length 1 Rafter Length = Plan Length x Rafter Length per metre (RL/m) Rafter Length = x 1.103 Rafter Length = 1479

Step 4 – Determine Rise (If Required) Centreline Length
1479 625 1.103 0.466 25° 1341 Plan Length 1 Total Rise = Horizontal Travel x Rise per metre Total Rise = 1341 x 0.466 Total Rise = 625

Overhang on a Plan is always measured from external wall

Determine Rafter Length Mathematically (Version 1)
In this case Timber Famed Wall Determine Rafter Length per m = 1 ÷ cos 25 = per m Rafter = Run x 1.103 = x 1.103 = 1.480 Roofing calculations are always measured from Birdsmouth or pitching point Rafter 90 x 45 Ridge 125 x 19

In this case Timber Famed Wall Determine Total Rafter Length Rafter = Plan Length x 1.103 = x 1.103 = 1791 x 1.103 = 1.975 Roofing calculations are always measured from Birdsmouth or pitching point Rafter 90 x 45 Ridge 125 x 19

In this case Brick Veneer Wall O/H = = 600mm Total Rafter Length = x 1.103 = 1961 x 1.103 = 2.163 Rafter 90 x 45 Ridge 125 x 19

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

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

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

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

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

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

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

Using Similar Triangles 1341/500 = 2.682 or = 2 r 341
Step out 2 full triangles Select Start Point Allowing for O/H

Intersection of Top of Rafter & Edge of Square

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

Determine Roofing Angles used 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 Cut Foot Cut

Determining Angles Mathematically
Extend Line 90⁰ From Rafter

Extend Line 90⁰ From Rafter Extend Plumb Line

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

This angle must be 65⁰ 90 – 25 = 65 Right Angled Triangle Roof Pitch This angle must be 25⁰ 90 – 65 = 25

Extend Line 90⁰ From Rafter

Extend Line 90⁰ From Rafter Extend Plumb Line from same origin at top of Rafter

Extend Line 90⁰ From Rafter Extend Plumb Line from same origin at top of Rafter Angle Formed is same as roof pitch

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

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

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

Complete Q5 in Workbook

Determine Roof Angles Graphically
Plan – View We can only see rafter run

Extend Top Plate & Ridge

Extend Top Plate & Ridge Mark Rise

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

Steps In Construction Gable Roof
Physically Confirm Span & Plates are Parallel Calculate True Rafter, Rise & Plumb cuts Mark out ceiling joists, rafters & ridge Install Ceiling Joists Cut Pattern Rafter & test to confirm Cut required rafters & install

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

Determine Rafter Length
Span = 6900 Pitch 24°

Span = 6900 Pitch 24° 1

Span = 6900 Pitch 24° 0.4451 1

Span = 6900 Pitch 24° Rafter =√ ( ) 0.4451 1

Span = 6900 Pitch 24° 1.095 Rafter =√ ( ) = 1.095 0.4451 1

Span = 6900 Pitch 24° Rafter = 1

Span = 6900 Pitch 24° 1.095 Rafter =1 ÷ Cos 24° 1

Span = 6900 Pitch 24° 1.095 Rafter =1 ÷ Cos 24° = 1.095 1

Span = 6900 Half Span = 3450

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

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

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

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

Span = 6900 Half Span = 3450 Run = 3450 – 9.5 = True Length = / cos 24 =3766 Overhang = 450/cos 24 = 493 Total Rafter = 4259 Allow for plumb cut = 41 Minimum Rafter Length = 4300 Order = 4500 Allow for Plumb cut Tan (Pitch) x Width = Tan 24° x 90 = 41

Estimating Sheet

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

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

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) =

Estimating Sheet

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

Estimating Sheet

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

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

Estimating Sheet

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

Estimating Sheet

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

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

Estimating Sheet

One Row of Purlin Each Side

Gable Roof Common Rafter

Top Plate Part of the Wall Frame Takes structural load from Roof
Size must be determined from span tables

Top Plate

Exercise 1 Determine Required Top Plate Size

Birdsmouth Max 1/3 Depth of Rafter

Gable Roof BCGCA3007B.

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