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© TAFE NSW Construction and Transport Division 71

BROKEN HIP and VALLEY ROOFS

These roofs are created when a hip roof is built on an irregular shaped base having a number of different spans. When the wall frame plan resembles a ‘T’ or ‘L’ shape, each span will have its own hip roof. Where these hip roofs connect with one another a ‘Broken hip’ is created, which ties the higher ridges to the lower ridges.

PART 2 :

Fig. 95 Typical Broken hip and Valley roof

HIP and VALLEY ROOFING


TYPICAL BROKEN HIP and VALLEY ROOF SHAPES

Fig. 96 Typical roof shapes formed

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MEMBER NAMES and POSITIONS

Fig. 97 Broken Hip and Valley roof members



DETERMINING THE POSITION OF THE BROKEN HIP

Fig. 98 Diagramatic sketch

The plan view shows how the major and minor ridges are linked together by the broken hip. The broken hip is simply a shortened version of the full length member, which would be placed here if it was a standard hip roof.

Fig. 99 Detail ‘A’ Broken Hip and Valley

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ALTERNATIVE METHOD - Junction of minor span, ridge, broken hip and valley.

Fig. 100 Alternative method



ERECTING THE ROOF Commencing with the roof of the major span, it is common practice to fill in as much of the roof as possible. During the erection of the minor span, it may be necessary to provide a temporary prop to support the ridge.

Fig. 101 Steps to follow during erection process

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MEASURING-IN THE BROKEN HIP

Fig. 102 Method of measuring-in



CALCULATING LENGTH: Cripple Crown End and Centring Rafter STEP 1: Determine Plan Length To set out and calculate centre-line length of the cripple crown end and centring rafters, the plan length must be determined. The difference between the two spans involved will give the plan length of the required member, as shown below:

Fig. 103 Calculating the length of nominated members

Example 1:

Difference between Major Span and Minor Span = 12.100—6.900 = 5.200

Difference between Major Span and Minor Span = 12.100 - 8.700 = 3.400

12 100

8 700

6 90

0

PLAN

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STEP 2: Set Out Length of Cripple Centring Rafter When the plan lengths have been established, the rafters are set out by stepping down the pattern rafter using the steel square, or calculating the length by using the true length of the common rafter per metre run and measuring the distance. Note: It’s good practice to use both methods to provide a check against the other.

Fig. 104 Steel square set out



Example 2: Determine the length of the cripple centring rafters:

Fig. 105 Length of cripple centring rafters

Set out for Cripple Centering Rafters

Rafter ‘A’ Plan length is the difference between Major and Minor Span = 9.500 - 8.500 = 1.000

Rafter ‘B’ Plan length is 1.00 plus the length of the ridge: = 1.000 + 3.500 = 4.500 When the ridge length = 13.000- 9.500 = 3.500

13 000

Equal

Equa

l

Raf

t er B

B

A 9 50

0

8 500 4 500

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CALCULATING LENGTH: Cripple Creepers STEP 1: Determine Length to the Top End To set out and calculate centre-line length of the cripple creeper rafters, the plan length must be determined. To determine the top position of Cripple Creeper Rafter A, shown on the roof plan, step down two rafter spacings from the crown end, i.e. (600 x 2 = 1200 mm). This will be the top position of the first cripple creeper.

Fig. 106 Plan length layout of creeper rafters

6 600

Raf

ter ‘

B’ Rafter ‘B’

Difference between Major and Minor span: = 12.000 - 6.600 = 5.400

Remaining Cripple Creepers are stepped, reducing from the top and bottom of creeper long points.

Raf

ter ‘

A’

6 900 5 100

Difference between half the Major span and the full Minor span.

“a”

“a”



STEP 2: Determine Length to the Bottom End To determine the bottom position of Cripple Creeper Rafter A, step up from the birdsmouth the distance equal to the difference between half the Major span and the Full Minor span repre-sented by ‘a’, shown on the roof plan. ‘a’ = (2 rafter spacings) - (the difference between half the Major span and the Full Minor span ) = ( 2 x 600) - ( 6000 - 5100) = 1200 - 900 = 300 Therefore, ‘a’ = 300 mm STEP 3: Determine Plan Length of Cripple Creeper ‘A’ To determine the final plan length of the first cripple creeper, deduct the top and bottom reduc-tions from the length of the crown end (half Major Span): Plan length = Half Major Span - (top reduction + bottom reduction) = 6000 - (1200 + 300) = 6000 - 1500 = 4500 Therefore, the plan length of the first cripple creeper ‘A’= 4500 mm STEP 4: Determine Plan Length of Other Cripple Creepers To determine the plan length of the other cripple creepers, simply deduct one (1) rafter spacing from the top and one (1) rafter length from the bottom, i.e. deduct 1200 mm off each preceding rafter. STEP 5: Determine Set Out Length of Cripple Creepers To determine the set out length, simply multiply the plan length by the true length per metre or step down using a steel square. STEP 6: Determine Set Out Length of Cripple Crown End rafter ‘B’ To determine the length of cripple crown end ‘B’, deduct the Minor Span from the Major Span. The difference will the plan length of the member. Rafter ‘B’ = Major Span - Minor Span = 12000 - 6600 = 5400 Therefore, the plan length of the cripple crown end = 5400 mm.

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CALCULATION OF IRREGULAR SHAPES Calculation of basic irregular shapes is dealt with in chapter 4 of “Basic Building and Construction Skills”. The following details relate specifically to irregular surfaces encountered in residential construction; Roof Shapes “Many surfaces of buildings and associated structures require accurate measuring so that specific materials may be ordered to carry out the project.” This is especially true of roof shapes, which may range from a very simple surface form to a very complicated one. Therefore some understanding of how they relate to oneanother and the commonalities between them is an essential part of the surface area calculation process. This may be best demonstrated by comparing the simple gable to a hipped roof. Although both are different in appearance, i.e. one has two sloping surfaces and the other has four, they have exactly the same surface area. Therefore, logically the same formula for surface area should be able to be applied to both, e.g.: Example 1: Calculate the area of each surface area of the gable roof shown below:

Fig. 107 Surface development of a typical gable roof

Formula = Length of the inclined surface x Length of the wall plate

= 3.135 x 7.250

= 22.729m²

Therefore, the total for both sides = 22.729 x 2 = 45.458m²

3135

1550

5450

True length of inclined surface

Section

True shape of

roof surface

Plan Length of wall plates

7250



Example 2: Calculate the area of each surface area of the hipped roof shown below, when the length of the incline and the length of the wall plate is the same as the gable roof:

Formula = Length of the inclined surface x Half the base = 3.135 x 5.450

2 = 3.135 x 2.725 = 8.543m²

Formula = Length of the inclined surface x Average length of wall and ridge = 3.135 x 7.250 + 1.8

2 = 3.135 x 4.525 = 14.186m²

= 8.543 x 2 + 14.186 x 2 = 17.086 + 28.372

= 45.458m²

Therefore, the total for all (4) sides = 45.458m²

3135

1550

True length of inclined surface

Section

A

B

True shape of

surfaces

7250

5450

Fig. 108 Surface development of a typical hipped roof

SIDE A

SIDE B

Total surface area Multiply each surface by two (2) and add the totals together:

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Conclusion Therefore, when the length of the surface incline and the average length of the wall plates are the same, both roofs will have exactly the same surface area. This means that the same simple formula for the gable roof could be applied to the hipped roof, which would prevent a needless waste of time caused by using the longer hipped roof version. CALCULATION OF ROOF TILES Once the total surface area of the roof is known, the roof covering may be calculated and ordered. The same area is used when calculating materials for a gable or hipped roof to calculate sarking, roof sheets or in this case the number of roof tiles required: Example 1: Calculate the quantity of ‘Monier’ concrete ‘Shingle profile’ roof tiles, with a 100 mm head lap, when the average coverage is equal to 10.6 tiles per m²;

Formula = Area of the roof x Average number / m² = 45.458 x 10.6 = 481.855

Formula = Total roof tiles 100

x Cost plus delivery / 100

= 506 100

x $136.19

= 5.06 x $136.19

= $689.12

Therefore, the total cost of roof tiles delivered is $689.12

= 481.855 x 1.05 = 948Say 506

Therefore, order 506 tiles. (or to the nearest pallet)

Cost Calculate the total cost of the ‘Shingle profile’ tiles, including delivery, when they cost $135.00/100 tiles plus an additional $1.19/ 100 for delivery;



CALCULATION OF HIP AND RIDGE CAPPING Using the detail below, it is possible to calculate the length of the roof surface incline, the plan length of the hip, the true length of the hip and the length of the ridge.

Formula = ½ span² + rise²

= 2.725² + 1.550²

= 7.426 + 2.403

= 9.829 = 3.135m

Length of Ridge 7250

5450

SPAN

2725 ½ SPAN

2725

1550

1550

'A'

Incli

ne L

engt

h Plan Length

'B' True Length of Hip

Incline Length

'A'

½ SPAN

RIS

E Length of Roof Surface Incline Using the standard ‘Pythagorean theorem’, calculate the inclined length of shape ‘A’

Therefore the true length of the surface incline = 3.135m

Fig. 109 Calculated proportions of a hipped roof

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Plan Length of the Hip When viewed on plan, the angle of this member is at 45°. If the end of the line, at the hip and ridge intersection, is projected to the wall plates on both sides at 90° a square will be formed, as shown below:

Formula = Length of one side (½ span) x Constant 2.725 x 1.414 = 3.853m

Formula = Plan length of hip² + rise²

= 3.853² + 1.550²

= 14.846 + 2.403

= 17.267 = 4.155m

2725

½ SPAN

45o

2725 ½ SPAN

Plan Length

True Length of Hip

'B'

Ris

e

Note:When a diagonal line is drawn corner to corner within a square, a 45° angle is formed. To calculate the length of this 45° line a ‘constant’ of 1.414 is used. If any side of the square is multiplied by this constant, then the length of the 45° line will be found, as follows: Therefore the plan length of the hip will be = 3.853m

True Length of the Hip Using the standard ‘Pythagorean theorem’, calculate the true length of the hip to shape ‘B’

Therefore the true length of the hip will be = 4.155m

Fig. 110 Forming a square in the roof



Length of the Ridge When viewed on plan the length of the ridge is seen as being in a distance equal to the ½ span at both ends. Therefore, if the full span is deducted from the total wall plate length, the resulting measurement will be equal to the length of the ridge, as shown below:

Formula = Length of the wall plate - Full span = 7.250 - 5.450 = 1.800m

2725

½ SPAN

Ridge Length 2725

½ SPAN

7250

1800 4155

Therefore the resulting length of the ridge will be = 1.800m Quantity of Hip and Ridge capping Using the calculated lengths for the hips and ridge it is possible to work out the number of hip and ridge capping pieces to cover the roof:

Fig. 111 Plan of roof member outline

Fig. 112 Hipped roof showing lengths of hips and

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Formula = Length of hips x 4 + Length of ridge

= (4.155 x 4) + 1.800 = 16.620 + 1.800 = 18.420m

Formula = Total hip and ridge length

÷ Effective cover of capping

= 18.420 ÷ 0.380

= 48.470 Say 49 Therefore, the number of pieces required is 49



CALCULATION OF SURFACE MATERIALS: for a BROKEN HIP & VALLEY ROOF

The following details outline the procedure to calculate roof tiles, ridge and hip capping, eaves soffit linings and quantity of eaves soffit bearers, when: Specification: • Roof Pitch is 1 : 2.75 • Width of eaves is 450 mm • Allow 12 tiles per m² and 4 hip and ridge tiles per m • Soffit bearers are spaced at 600 centres.

Fig. 113 Plan of a typical hip & valley roof

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1. NUMBER OF ROOF TILES

STEP 1

= 1.000 2.750

Rise per metre run of common rafter:

= 0.364

STEP 2

= 0.364² + 1.0²

True length of common rafter per metre run of common rafter:

= 0.132496 + 1.0

= 1.132496

= 1.064

STEP 3

Span A = 2.950 x 1.064

Ordering lengths of common rafters:

= 3.139

Span B = 2.850 x 1.064

= 3.032

Span C = 2.700 x 1.064

= 2.873

STEP 4 Area of the roof:

Span A = 2 (Roof length x Rafter length)

= 2 x (15.300 x 3.139)

= 96.053 m²

Span B = 2 x (4.6 x 3.032)

= 27.894 m²

Span C = 2 x (2.100 x 2.873)

= 12.067 m²

= 96.053 + 27.894 + 12.067 Total Area of Roof

= 136.040 m²

NUMBER OF TILES = 136.040 x 12 (tiles per m²)

= 1632.168, say 1633 tiles required.



2. NUMBER of RIDGE and HIP CAPPING TILES STEP 1 Ridge lengths:

Span A = 14.400 - 5.000

= 9.400

Span B = 9.600 - (4.800 + Difference between spans)

= 9.600 - (4.800 + 0.200)

= 9.600 - 5.000

= 4.600

Span C = 7.100 - (4.500 + Difference between spans)

= 7.100 - (4.500 + 0.500)

= 7.100 - 5.000

= 2.100

= 9.400 + 4.600 + 2.100 Total length of ridge capping

= 16.100 m

STEP 2 True length of hips per metre run:

= 1.414² + 0.364²

= 1.999 + 0.132

= 2. 131

= 1.460

Therefore length of full Span A = (4.800 + 0.900) x 1.460

2

= 2.850 x 1.460

Span B = (4.500 + 0.900) x 1.460 2

= 2.700 x 1.460

Span C = (5.000 + 0.900) x 1.460 2

= 2.950 x 1.460

length hips (including eaves width):

= 4.161

= 3.942

= 4.307

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STEP 3 Length of broken hips:

Span A = Difference between half spans x T.L. hip /m run

= (2.500 - 2.400) x 1.460

= 0.100 x 1.460

= 0.146

Span B = Difference between half spans x T.L. hip /m run

= (2.500 - 2.250) x 1.460

= 0.250 x 1.460

= 0.365

STEP 4 Total length of hips:

Span A = 4.161 x 2 hips

= 8.322

Span B = 3.942 x 2 hips

= 7.884

Span C = 4.307 x 2 hips

= 8.614

=

8.322 + 7.884 + 8.614 + 0.511

Total length of capping

Broken hips = 0.146 + 0.365

= 0.511

= 25.331 m

NUMBER OF TILES

=

25.331 X 4 (caps per metre)

= 101.324, say 102 capping tile pieces.



SPECIAL SHAPED ROOFS Common roof types, such as the gable and hip, may be modified or altered to change their appearance and give a building a whole new character. The early part of the 20th Century saw vast number of roof styles appear, which were based on many existing types being constructed in Britain and Europe. Some of these roof types included the Gambrel (also known as a Dutch gable) and the Jerkin Head (also known as a Hipped gable or a Clipped gable).

Many of the earlier Gambrel types also had louvred vents at either end to allow cross air flow, which assisted with internal room temperature control by allowing the trapped heated air to escape. Other variations to this roof type include a bellcast on the hip end where an obtuse or reflex angle is formed between the end of the ridge and the pitch of the hip end. Most of the modern Gambrel types have decorative cladding, which closes the ends off and allows the roof tiled surface to be broken up and highlighted.

Fig. 114 Gambrel roof Fig. 115 Jerkin head roof

Fig. 116 Typical Gambrel ended hip roof

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GAMBREL The effect of the gambrel ends is produced at the span ends by combining gables with a hipped roof. The gables are formed by extending the ridge board past the hip and ridge junction and then filling-in the extension like a gable.

Fig. 117 Typical gambrel shape

The small gables, or gablets, produced may be clad with a range of materials, such as flat fibre-cement sheet, timber weatherboards, Colorbond metal, Weathertex boards, Hardi-plank boards, etc. Generally, a timber barge board is used to finish the junction between the roof tiles and the sheeting on the gable, with a lead flashing sealing the joint between the gable cladding and the tiled roof surface. Where the verges are not pointed, a Colorbond barge and barge soaker/gutter system may be used.

Fig. 118 Colorbond barge and barge soaker/gutter

Isometric View

Plan



Preparing The Gambrel End

The lead should be coated with paint, plastic, rubber or bitumen to avoid galvanic action between dissimilar metals occurring. The bottom of the lead flashing should be set a minimum of 90 mm above the jack rafters to allow for tile battens and a course of roof tiles to fit under with ease. Note: Roofing lead exposed to temperatures of 40° C, or above, for prolonged periods will cause the lead to grow up to 2 mm in any 2.0 m length. This inevitably ends up causing stress splits in the width of the lead and leakage will occur.

Fig. 119 Positioning the lead flashing

The lead flashing, usually 230 mm wide min., is laid across the width of the gambrel. It is turned up behind the cladding, minimum of 50 mm, and beaten over the profile of the roof tiles to form a waterproof seal. The lead flashing should be a minimum of 1.8 mm thick, also referred to as 20 kg lead, and run the full width of the gambrel plus a minimum of 300 mm either side of the hip centre. There must be an allowance for expansion of the lead due to heat absorption, therefore the maximum length of any one piece should be 2.0m lapped a minimum of 150 mm.

Fig. 120 Alternative gambrel end preparation and finish

Fixing through sheet

20kg Lead flashing

Jack rafter

Position of roof battens and tiles

Walling plate

Dutch-hip and rafters

F.C. strip to

Barge Lead flashing extended

Hip tiles Sarki

100

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Constructing The Gambrel

STEP 1 Extend the ridge to the desired length in increments of rafter spacings. The most common method is to allow for a longer ridge during original construction, however the ridge may be extended later by strapping or fish-plating extensions to the end of the normal length hip roof ridge.

Fig. 121 Extending the ridge on centre line by rafter spacings.

Fig. 122 Alternative method of extending the ridge

PLAN VIEW

Three additional pairs of common rafters required on this case.

Run of gambrel rafters Hip, line of intersection on plan

Set out rafter positions on the plates

Centering rafter

Long hip

Jack or crown-end rafter fitted under ridge extension

Ridge extended as required

Galv. steel strap or nail plates

Creeper

Extended hip

Jack or crown-end rafter Long hip

Hip

Centering rafter



STEP 2 Temporarily prop the end of the ridge to prevent sagging. Plumb up from the string line position, mark the end of the ridge and cut to length. Fit pairs of common rafters at the marked spacings to frame up the end.

STEP 3 Determine the position of the jack rafters and height of pitching plate by plumbing up the outside faces of the rafter plate positions onto the last pair of common rafters (Gambrel end rafters). This also determines the cutting length of the jack rafters.

Fig. 123 Prop end of ridge

Fig. 124 Determine position and length of jack rafters.

Brace

Plumb line String line

Prop

Adjust ridge for height marked on prop. Centre up and plumb to line. Check for level and then secure brace.

Gambrel rafter may be held against common rafter to obtain this point

Locating position for pitching plate

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STEP 4 Lay the pitching plate on the wall plate and transfer the rafter set outs onto it. Fit the inside edge of the pitching plate against the Gambrel rafters, measured the length of the plumb cut common rafter down. Align the outside of the first jack rafter with the set out mark on the gambrel rafters and bolt the pitching plate into place.

Fig. 125 Set out pitching plate and fix into place

STEP 5 Notch ends of jack rafters and fix into place using a string line to maintain a constant straight line.

Fig. 126 Fix jack rafters into place

Bolt to rafters

Position & level the pitching plate

Place at bottom of plumb line

Transfer rafter set-out from end-wall plate onto the pitching plate

Rafters notched over pitching plate level with string line

Creeper

Short hip

String line Pitching plate

Gambrel rafters

NOTE: In the case of tiled roofs, rafters must work full tile courses.



Note: Prepare ends of jack rafters, as shown below. Set out, cut and fit the short hips into place, as shown below.

Fig. 127 Notching jack rafters Fig. 128 Fitting string line

Fig. 130 Assemble hips Fig. 129 Determine hip measuring point

STEP 6 Fit gambrel end trimming studs and ceiling trimmers. Fit collar ties as required.

Fig. 131 Complete the framing to the gambrel end

Fit gable trimming studs and fix lining. Fit barge boards and flashing.

NOTE: Hanging and strutting beams have been omitted for clarity.

String line

Pitching plate

Gambrel rafter

String line Plumb line

Pitching plate

Fixing point marked on common rafter

Short hip

Short hip measured from this point

Half mitre measured & marked

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Alternative Gambrel Construction Method

Fig. 132 Alternative method



Methods Used for Small Spans

Fig. 133 Use of ridge extension

Fig. 134 Framing onto hip for small gambrel end

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Determining the Length of the Ridge The ridge may be extended by any length, but for convenience of construction it is usually extended by rafter spacings. Once the length has been determined the ridge is set out as for gable and hip roofs, i.e. laying the ridge along the top wall plate and transferring the rafter set out positions directly onto it.

Fig. 135 Typical Gambrel roof plan

STEP 1 Determine the length of the ridge between apex points:

=

=

=

Length of roof - Span of roof 7.200 - 4.500 2.700 m

STEP 2 Determine the length of the ridge extension at each end, based on rafter spacings:

=

=

=

=

(3 Rafter spacings) x 2 (3 x 0.450) x 2 1.350 x 2 2.700 m

STEP 3 Add the lengths together to find the total length:

=

=

2.700 + 2.700 5.400 m

STEP 4 As the length at this point is based on centre line length, half a rafter thickness must be added to each end to obtain the cutting length of the ridge. For this example the rafters are 35 mm thick:

=

=

Order:

5.400 + 35 5.435 m 1/ 5.7



JERKIN HEAD The shape of the Jerkin head is produced at the span ends by combining hips with a gable roof. The hips are formed by extending the ridge board past the standard apex position for a hip roof and creating a soldier wall on top of the end wall to form the part gable.

Fig. 136 Typical Jerkin head details

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Determine Position and Length of Soldier Wall Similar to the Gambrel roof, the ridge is extended at both ends by standard rafter spacings. The length of the ridge extension will be equal to the distance in from the outside walls to the soldier wall. Therefore, the length of the soldier wall will be:

Span - (length of the ridge extension) x 2 The height of the soldier wall will be a direct ratio to the roof pitch. This means that the height of the wall is equal to the ridge extension by the rise per metre run:

Ridge extension x Rise per m run

Fig. 137 Soldier wall proportions

1. The length of the wall in this example will be:

= 4.800 - (1.350 x 2) = 4.800 - 2.700 = 2.100 m 2. Say, the roof is pitched at 22° then the height of the wall will be: = 1.350 x 0.404 = 0.545 m

Ridge extension

Height of Soldier Wall

Soldier wall support to Jerkinhead

Side Elev. Jerkinhead roof

Jerkinhead & Soldier Wall



Forming the Jerkin Head The set out and construction of the Jerkin head is similar to the process required for a standard hip roof. The main difference being the new span will be the length of the formed soldier wall.

STEP 1 Extend the ridge by rafter spacings, similar to the Gambrel roof. In this example, the ridge is extended by 3 rafter spacings, i.e. 3 x 0.450 = 1.350 m

STEP 2 Construct the soldier wall, based on the measurements in the previous figure 137., i.e. 2.100m long x 0.545m high

STEP 3 Set out the position of the crown end and creeper rafters at 0.450 m spacings, as for a standard hip roof.

STEP 4 Set out, cut and fix crown end, hips and creepers to sit on the soldier wall, based on the same pitch as the main roof.

SUMMARY Therefore, once the ridge extension has been determined, the soldier wall sizes de te rmined , the so ld ie r wal l constructed and placed in position, the construction of the Jerkin head end is exactly the same as for a hip roof.

Fig. 138 Determine new apex position

Fig. 139 Set out as for a hip roof

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BASIC CALCULATIONS for GAMBREL and JERKIN HEAD ROOFS The following example outlines the procedure for calculation of the members listed: 1. Set out and ordering length of the common rafter for the main roof; 2. Set out and ordering length of the common rafter for the Gambrel roof; 3. Calculation of the height of the soldier wall; and 4. Set out and ordering length of the common rafter for the Jerkin head roof.

SPECIFICATION Pitch Ratio 1: 1.680 Span 6.300 m Rafter spacings 0.600 m Brick veneer construction Eaves width 0.450 m Ridge extended by 2 rafter spacings to form Gambrel end Ridge extended by 3 rafter spacings to form the Jerkin head

Common Rafter for Main Roof

1. Rise per metre run of Common Rafter:

= 1.000 1.680

= 0.595

2. True length of Common Rafter per metre run of Common Rafter:

= √ 1.0² + 0.595²

= √ 1.0 + 0.354025

= √ 1.354025

= 1.164 m

3. Set out length for Common Rafter for the Main Roof:

= 6.300 x 1.164 2

= 3.150 x 1.164

= 3.667 m

= (Half span + eaves width + brick and cavity) x True length per metre run

4. Ordering length of Common Rafter for Main Roof:

= (3.150 + 0.450 + 0.150) x 1.164

= 4.365 m, Order 4.5 m



Height and Length of Soldier Wall

1. Deduction from span of Main Roof (each side):

= 3 x Rafter spacings

= 3 x 0.600

= 1.800 m

2. Height of Soldier Wall:

= Deduction x Rise per metre run

= 1.800 x 0.595

= 1.071 m high

= Span of main roof - (2 x deduction)

3. Length of Soldier Wall:

= 6.300 - (2 x 1.800)

= 6.300 - 3.600

= 2.700 m long

Common Rafter for Gambrel Roof

1. Set out length for Common Rafter for the Gambrel Roof:

= [Half span main roof - (2 x Rafter spacings)] x True length per m run

= [3.150 - 1.200] x 1.164

= 1.950 x 1.164

= 2.270 m

2. Ordering length of Common Rafter for the Gambrel Roof:

= (Gambrel half span + eaves width + brick and cavity) x True length per m

= (1.950 + 0.450 + 0.150) x 1.164

= 2.550 x 1.164

= 2.968 m, Order 3.0 m

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Crown end Rafter for Jerkin Head

1. Set out length for Crown end Rafter for the Jerkin head Roof:

= Half span Jerkin Head x True length per m run

= 2.700 x 1.164 2

= 1.350 x 1.164

= 1.571 m

2. Ordering length of Crown end Rafter for the Jerkin Head Roof:

= (Jerkin Head half span + eaves width + brick and cavity) x True length per m run

= (1.350 + 0.450 + 0.150) x 1.164

= 1.950 x 1.164

= 2.270 m, Order 2.4 m



SCOTCH VALLEY CONSTRUCTION This method is used as an alternative to conventional construction to form a valley. The valley board is replaced with a ‘Lay board’, which is laid on top of the rafters to form a fixing platform for the feet of the minor span valley creepers.

Fig. 140 Application of the scotch valley

The scotch valley is mainly used where an addition is added to an existing building. It provides a quick and very efficient method of construction, requiring little or no disturbance to the existing roof. The existing rafters remain in place to support the lay board, which in turn supports the feet of the valley creepers. This system may also be adapted for use where dormer windows are built into existing roofs.

Fig. 141 Scotch valley construction

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Method of Construction The following method is applied to roofs having the same pitch.

Fig. 142 Obtaining ridge height

Fig. 143 Framing up the minor span

STEP 1 Locate the height of the minor span ridge on the common rafters of the existing main roof.

STEP 2 Position the ridge and rafters to form the minor roof.



STEP 3 Measure the length of the lay board, then cut and fix into position.

STEP 4 Measure the length of the longest creeper. Use plumb bevel common rafter for the top of the creeper and level bevel common rafter and edge bevel creeper for the compound foot cut. The remainder of the creepers can be set out using the steel square or by calculating a deduction from long point to long point.

Fig. 144 Measuring the lay board

Fig. 145 Cutting and fixing the valley creepers

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Adjacent - Means it is placed next to or found beside something.

Apex - This is the very top or point of something, like the apex of a roof, meaning where members come together at a common top position.

Bisect - This means to cut, separate or divide something exactly in half, such as when a 90° angle is bisected it becomes two 45° angles.

Circa - This means around, approximately, round about, etc. Usually refers to dates when estimating the age of a building or structure such as circa 1854, also written as (c 1854).

Cluster - This is a term, which refers to a group or gathering of a number of members in a frame, such as a roof cluster, which consists of the end of the ridge, two centring rafters, a crown end rafter and two hip rafters.

Complimentary - In this case it means any two angles, which make up a right angle.

Constant - In this case it means a number, quantity or amount, which is used as the basis for several calculations. For example the length of 1.414m is a constant, which may be used to calculate the 45° hypotenuse length of a right-angled triangle, once the length of one side is known.

Corbelled - Refers to stepped out brickwork used to support other members, such as corbelled eaves.

Dihedral - This is the angle formed between any two surfaces where they meet along a common length, such as a ridge in a roof. A dihedral angle is formed between the underside of the two roof surfaces or where a roof surface meets a parapet wall, etc.

F.C. - This is an abbreviation for fibre cement, similar to the product ‘Hardiflex’.

Hypotenuse - This is the angled side of a right-angled triangle.

Inclined - Means to be at an angle to something, such as an inclined strut or brace.

In-situ - This is an abbreviated version meaning in situation or position, such as pouring concrete in-situ, meaning to pour in place into the formwork.

In-to-over - This is a method used for marking the spacings of members. It literally means marking from the inside face or edge of one member to the outside face or edge of the next member. It is equal to working centre-to-centre but is more practical for fixing purposes as it allows one edge to be lined up with the mark, so it is easily seen, ready for fixing.

Lined on-the-rake -

This is a term used to describe the ceiling lining of a pitched roof, which is fixed to the underside of the rafters. There is no access to the roof structure as there is no roof space formed.

Parapet - This is a vertical wall or gable, which extends past the line of the roof to enclose the roof from view. The parapet is usually constructed of brickwork or timber framing and clad with sheet material.

Patent - This is a term used to describe a product which has had its design registered with the Patents office. It is the original idea of a person or persons, which cannot be copied without consent.

GLOSSARY OF TERMS



Primed - This is a protective white or pink paint coating applied to timber before it is fixed into place. It seals the timber and provides a surface ready to take undercoat paint prior to the finishing coats. It helps to prevent timber decay from occurring.

Scribe - This is where the shape of one piece is to be fitted to the surface shape of another. It may also refer to anything placed in-situ and marked to suit the final resting position of that member, such as scribing a hip in position.

Slat - Refers to a thin narrow piece of timber or several thin arrow pieces put together to make something else, such as slats of timber used to make a sheet of lattice.

Soffit- This is the horizontal under face of a structure or lining. The eaves soffit is the underside face of the eaves sheeting.

Trapezoid - This is an irregular quadrilateral with only two parallel sides. The shape may be found on the side roof surface of a hip roof made up of the fascia, ridge and two hips

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FURTHER READING

Australian Standards Committee, 1992, AS 1684 – National Timber Framing Code, Standards Association of Australia Homebush, Sydney. Bloomfield, F. C. and E. Peterson, Revised by B.S. Brown and H. A. Slatyer, First Edition 1958, Fifth edition 1985, The Australian Carpenter and Joiner – volumes 1 & 2, Standard Publishing Co. Pty Ltd., Naremburn, NSW. Simpson, Charles & Barry Hodgson, 1995, Building a house – framing practices, Macmillan Education Australia, South Melbourne. Staines, A., Reprinted 1987, Owner Builders & Renovator, Pinedale Press, Caloundra, Qld. Staines, A., First Edition 1988, The Australian Roof Building Manual, Pinedale Press, Caloundra, Qld. Staines, A., Reprinted 1988, The Australian Owner Builders Manual, Pinedale Press, Caloundra, Qld. Stapleton, M. and Ian Stapleton, 1997, Australian house styles, The Flannel Flower Press Pty Ltd, Mullumbimby, NSW Teachers of Building, 1996 Reprinted 1997, 1998, Second Edition 1999, Basic Building and Construction Skills, Addison Wesley Longman Australia Pty Ltd, South Melbourne. Ward-Harvey K., 1984, Fundamental Building Materials, Sakoga Pty Ltd, Mosman NSW.

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