Flat Roof & Introduction to Gable Roof

Created by Michael March 2004 / reviewed march 2008

Flat roof construction P23 & 24 in Carp 11 Flat roofs combine the roof and

ceiling frame in one Generally 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 types

Ceilings 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 Single sloping roofs Walls at either end of roof at

different heights Internal walls parralell to end walls

will be at different heights Walls at 90 deg. to end walls will

taper in height under the sloping rafters / joists

Two ceiling designs

Lean – to – Roof construction This type is constructed against an

existing wall or other roof Simple extensions Carports Verandahs Awnings

Rafter / Ceiling variations Common on carports, open

exposed rafters

Other types

Simplest method of marking With skillion roofs the simplest

thing is to scribe the rafter over the supporting plates

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

Roof Components – Gable roof

Ridge

Collar tie

StrutPlumb cut

Span

½ SpanCeiling joist

Common rafter

Purlin

Tail piece

or overhang

Eave width or eave overhang

Component names

Gable roof definitions Complete answers on your work sheets Roof span: Is the horizontal distance

measured overall the wall plates

Span

Rise: Is the vertical height measured from the x – y line to where the upper edge of the rafters would intersect

Rise

Other Reference Other reference for gable roof

definitions and sketch – carp 11, pages 27 to 30