flat roofs & introduction to gable roofs
DESCRIPTION
Flat Roofs & Introduction to Gable Roofs. M. S. Martin / March 2004 / Reviewed & Combined March 2007, Reviewed March 2010. Review Ceiling Frame Calc’s. Spec for example following copy on blank paper. Joists 150 x 38 sawn Oregon @ 600mm centres, max. span 3.6m - PowerPoint PPT PresentationTRANSCRIPT
Flat Roofs & Introduction to Gable Roofs
M. S. Martin / March 2004 / Reviewed & Combined March 2007, Reviewed March 2010
Review Ceiling Frame Calc’s
Spec for example followingcopy on blank paperJoists 150 x 38 sawn Oregon @ 600mm
centres, max. span 3.6mTrimmers 100 x 38 sawn Oregon @
600mm centresHanging beam 240 x 45 hardwood, max.
span of 5.4mOn sketch following, draw in joists and
hanging beam to scale and indicate trimmer positions also.
Sketch picture belowallow 100mm for wall frames (not shown)
Internal room sizes shown4.100
3.300
8.350
5.800
Formula'sNo. of joists = width of room - 1 spacing
Length of hanging beam = length of room + 2 x wall thickness
Trimmers = length of wall – 1 spacing
Joists8.350 – 1.600= 13.916 – 1= say 14 – 1= 13
Order 13 @ 6.0m
Hanging beam4.150 + .200 = 4.350
Order 1 @ 4.5m
Trimmers5.800 – 1 = 9.666 – 1.600Say 10 – 1 = 9Trimmers at two ends plus internal wall9 x 3 = 27, 27 x .600 = 16.2 lin/m
Order 2 @ 6.0m, 1 @ 4.2m
Flat roof constructionBasic Roof & Ceiling Frame text – from
P23Flat roofs combine the roof and ceiling
frame in oneGenerally described as one with a
pitch less than 10 deg.To allow for extra loads the rafters /
ceiling jiosts are increased in sectional size
Ceiling typesCeilings can be either lined on the rake
or rafters laid flat and use graded battens to give fall to roof
Variations to ceilings
Skillion roofs – P 25Single sloping roofsWalls at either end of roof at different
heightsInternal walls parralell to end walls will
be at different heightsWalls at 90 deg. to end walls will taper in
height under the sloping rafters / joists
Two ceiling designs
Simplest method of markingWith skillion roofs the simplest thing is
to scribe the rafter over the supporting plates
Lean – to – Roof constructionP 26This type is constructed against an
existing wall or other roofSimple extensionsCarportsVerandahsAwnings
Rafter / Ceiling variationsCommon on carports, open exposed
rafters
Other types
Calculation of skillion rafters(eg) calculate the quantity of 125 x 50
rafters required for the roof 4.2m long and 2.7m wide, rafter spacings 600mm centres, the difference in height of plates is 900mm
Length of rafter = √ (run of rafter)² + (rise)²
No. of rafters = (length of building) + 1
spacings
Answer – length of rafter√ 2.7² + .900²= √ 7.29 + .81= √ 8.1= 2.846 lin/m
Order 3.0m lengths
2.700
4.200
900
Number of rafters (4.200) + 1 .600= 7 + 1 = 8
Order 8 @ 3.0m rafters
Gable Roofs and Components
Name the components (handout)
AnswersRoof Tiles
Tile Battens
Top Plate
Fascia
CorniceCeiling Joist
Ceiling Lining
Strutting Beam
Internal Wall
BlockTop Plate
Soffit Bearer
StudSoffit Lining
Anti-ponding Board
Collar Tie
RafterRidge
Purlin
Strut
Hanging Beam
Purlin
Strut
Gable roof definitionsRoof span: Is the horizontal distance
measured overall the wall plates
SpanPlate
Stud Section A-A
Definitions Continued½ Span : The Plan length of the rafter
Fig 22 Section through a gable roof
Half span or Run
Top plateCeiling joist
Common rafterStrut
Collar tieEqual
Plumbbevel
Ridge
Equal
Centre-lin
e
length
Actual le
ngth
Gauge linedepth
Ris
eH
eig
ht
DETAIL AT RIDGE BOARD
DETAIL AT PLATE
Birdsmouthnotch not greater than D/3
Centre-lin
e length of ra
fter
Overhang
Eave width
Level bevel
Plate line
Ris
e H
eig
ht
Fig 22 Section through a gable roof
Half span or Run
Top plateCeiling joist
Common rafterStrut
Collar tieEqual
Plumbbevel
Ridge
Equal
Centre-lin
e
length
Actual le
ngth
Gauge linedepth
Ris
eH
eig
ht
DETAIL AT RIDGE BOARD
DETAIL AT PLATE
Birdsmouthnotch not greater than D/3
Centre-lin
e length of ra
fter
Overhang
Eave width
Level bevel
Plate line
Ris
e H
eig
ht
Rise: Is the vertical height measured from the x – y line to where the upper edge of the rafters would intersect
Fig 22 Section through a gable roof
Half span or Run
Top plateCeiling joist
Common rafterStrut
Collar tieEqual
Plumbbevel
Ridge
Equal
Centre-lin
e
length
Actual le
ngth
Gauge linedepth
Ris
eH
eig
ht
DETAIL AT RIDGE BOARD
DETAIL AT PLATE
Birdsmouthnotch not greater than D/3
Centre-lin
e length of ra
fter
Overhang
Eave width
Level bevel
Plate line
Ris
e H
eig
ht
Fig 22 Section through a gable roof
Half span or Run
Top plateCeiling joist
Common rafterStrut
Collar tieEqual
Plumbbevel
Ridge
Equal
Centre-lin
e
length
Actual le
ngth
Gauge linedepth
Ris
eH
eig
ht
DETAIL AT RIDGE BOARD
DETAIL AT PLATE
Birdsmouthnotch not greater than D/3
Centre-lin
e length of ra
fter
Overhang
Eave width
Level bevel
Plate line
Ris
e H
eig
ht
Centre Line Length : The hypotenuse in the right angled triangle formed by the ½ span and the rise
Fig 22 Section through a gable roof
Half span or Run
Top plateCeiling joist
Common rafterStrut
Collar tieEqual
Plumbbevel
Ridge
Equal
Centre-lin
e
length
Actual le
ngth
Gauge linedepth
Ris
eH
eig
ht
DETAIL AT RIDGE BOARD
DETAIL AT PLATE
Birdsmouthnotch not greater than D/3
Centre-lin
e length of ra
fter
Overhang
Eave width
Level bevel
Plate line
Ris
e H
eig
ht
Fig 22 Section through a gable roof
Half span or Run
Top plateCeiling joist
Common rafterStrut
Collar tieEqual
Plumbbevel
Ridge
Equal
Centre-lin
e
length
Actual le
ngth
Gauge linedepth
Ris
eH
eig
ht
DETAIL AT RIDGE BOARD
DETAIL AT PLATE
Birdsmouthnotch not greater than D/3
Centre-lin
e length of ra
fter
Overhang
Eave width
Level bevel
Plate line
Ris
e H
eig
ht
Common Rafter : Is the member fixed to the ridge with a plumb cut and birdsmouthed over plate, extending to an eave.
Fig 22 Section through a gable roof
Half span or Run
Top plateCeiling joist
Common rafterStrut
Collar tieEqual
Plumbbevel
Ridge
Equal
Centre-lin
e
length
Actual le
ngth
Gauge linedepth
Ris
eH
eig
ht
DETAIL AT RIDGE BOARD
DETAIL AT PLATE
Birdsmouthnotch not greater than D/3
Centre-lin
e length of ra
fter
Overhang
Eave width
Level bevel
Plate line
Ris
e H
eig
ht
Fig 22 Section through a gable roof
Half span or Run
Top plateCeiling joist
Common rafterStrut
Collar tieEqual
Plumbbevel
Ridge
Equal
Centre-lin
e
length
Actual le
ngth
Gauge linedepth
Ris
eH
eig
ht
DETAIL AT RIDGE BOARD
DETAIL AT PLATE
Birdsmouthnotch not greater than D/3
Centre-lin
e length of ra
fter
Overhang
Eave width
Level bevel
Plate line
Ris
e H
eig
ht
Pitch : The amount of slope or gradient in a roof, typically expressed in degrees
30°θ
Continue on roofsRidge
Rafter
Purlin
Hanging beamCeiling joist
Strut
Set Out for Common RafterPlumb cut is at the
top of the triangleWe reduce the
centre line length of rafter by ½ the thickness of the ridge to get our true length
Birdsmouth has a maximum cut out of one third the rafter depth
Level bevel is shown here at base of triangle
Back of birdsmouth, is outside of frame and if you take a vertical line up, this is where it meets the x – y line
X-Y
LINE
Set Out on Steel SquareCalculate rise per / m. runTransfer to steel square
Reduced rise
Reduced run
Set out pattern rafterBy either stepping out with square, or by
calculation