Unit 4 - Roofs and roof framing plans
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Overview
In this unit you will examine the different types of roofs used in the Caribbean. You will learn the parts and components of a roof and how to draw sectional elevations, sectional details and roof framing plans.
Learning Objectives
After you have completed this unit, you should be able to:
Classify types of roofs
Identify types of flat and pitched roofs
Identify Parts of a roof
Identify Components of a roof
Prepare Plans and elevations of various types of roofs
Prepare working drawings of roof details
Section 1 – Classification of Roofs
The roof of a house refers to the framework of timber, steel or concrete on which a covering or thatch, corrugated sheets, asphalt etc. is attached.
Roofs are classified as either pitched or flat. Pitched roofs have a pitch exceeding 5° while flat roofs have a pitch not exceeding 5°. The pitch of a roof is the ratio between the rise and span of a roof.
Types of Roofs
Flat Roofs: Flat roofs may be constructed from lumber or concrete.
Pitched roofs:
Mono-pitched Roof (Shed Roof)
Hipped Roof
Gable Roof
Dutch Gable Roof
Saw Tooth Roof (Factories)
Folded Plate Roof (Factories)
Assignment 1
Describe the following types of roofs. Include a simple diagram for each.
Gable
Flat
Hipped
Mono-pitch
Dutch Gable
Saw tooth
What is the difference between a flat roof and a pitched roof?
Section 2.1 - Parts and Components of a Roof
Parts of a roof
Ridge: The highest part or apex of the roof.
Eaves: The overhanging or lowest part of a roof.
Gable End: A gable end is formed when a wall is carried up to the underside of the roof.
Hip: The edge or angle formed when two roofs’ surfaces meet to form an external angle which exceeds 180°.
Hipped end: The sloping triangular end of a hipped roof.
Valley: A depression resembling a valley, as the point at which the two slopes of a roof meet.
Components of a roof
Ridge Piece: The horizontal piece of timber forming the ridge and at which the common rafters meet.
Common rafter: A sloping timber extending from the ridge to the eaves of the roof.
Hip rafter: A rafter that extends from the hip to the eaves along the hip.
Valley rafter: A rafter that extends from the hip to the eaves along the valley.
Jack rafter: A short rafter between the hip rafter and the eaves or between the valley rafter and eaves.
Purlins: Horizontal timber in the roof at right angles to the rafters and carried on them to support lightweight roof covering.
Fascia Board: A type of roof trim that is commonly used on houses. It is mounted on the exposed ends of rafters or the top of exterior walls to create a layer between the edge of the roof and the outside.
Soffit Board: The soffit board is tucked away under the fascia board. The soffit can be ventilated to allow the flow of air into the roof area. Alternatively, ventilation can be provided over the top of the fascia board.
Wall Plate: A timber laid horizontally in or on a wall as a support for a girder, rafter, or joist.
King Post: an upright post in the center of a roof truss, extending from the tie beam to the apex of the truss.
Tie Beam: A horizontal beam connecting two rafters in a roof or roof truss.
Strut: A timber brace between the beam and the rafter used to resist longitudinal compression.
Roof Components
Pictorial Representation of Roof Frame
Section Through a Gable Roof (Roof Detail)
Assignment 2:
Sketch a section through a gable roof showing the following details:
Ridge
Rafters
Purlins
Fascia board
Soffit board
Struts
King post
Corrugates Galvanized steel sheets
Wall plate
Tie Beam
Ridge Cap
Section 3 – Roof Framing Plans
A roof framing plan is a plan view of the metal or wooden members of the roof frame without the roofing material attached. From the roof framing plan the external, Load bearing walls and wall plate are also indicated. The ridge falls in the center of a roof if the pitch on both sides is the same and the heights of the opposing walls are equal. For a hipped roof, unless the pitch of adjacent sides is different, from the plan view the sides meet at the hip at a 45° angle. Rafters and purlins from different sides usually correspond to increase the strength of the roof and for simplicity and neatness purposes. Placing purlins as close as possible to the ridge and as low as possible at the eaves add strength to the roof as it allows the roofing material to be secured to the roof frame at the lowest and highest points.
Drawing Hips
When drawing hips on floor plans, if the two inclined surfaces forming the hip have the same slope, the hip will always be at a 45-degree angle on the roof framing plan. Consequently, hip rafters are always represented at a 45-degree angle on floor plans, regardless of the roof's slope.
Designing and Drawing a Detailed Working Roof Framing Plan
Step 1: Understand the Building Shape and Design Considerations
Analyze the Building Shape: Identify the shape and size of the building. The roof design will depend on whether the building is rectangular, L-shaped, or any other form.
Review Building Codes: Familiarize yourself with local building codes and conventions regarding roof member sizes, spacing, and positioning.
Determine Roof Features: Decide on the placement of key roof features such as ridges, eaves, hips, and valleys based on the building’s design and your initial floor plan.
Step 2: Outline the Building Walls
Draw the Wall Outline: Start by accurately drawing the outline of the building walls to scale. This will be the foundation for your roof framing plan. Only include walls that will interact with roof members. In many cases only the external walls are necessary.
Step 3: Position the Ridge Member
Identify Ridge Locations: Determine where the ridge members (the horizontal lines at the peak of the roof) will be located.
Draw the Ridge Line: Draw the ridge line at the appropriate height and location on the roof framing plan.
Step 5: Include Hip and Valley Rafters
Identify Hip Locations: Locate where the hips (the external angle formed by the intersection of two sloping roof planes) will be on the plan.
Draw Hip Rafters: Draw the hip rafters at a 45-degree angle from the corners of the building towards the ridge, regardless of the roof slope.
Identify Valley Locations: Locate where the valleys (the internal angle formed by the intersection of two sloping roof planes) will be on the plan.
Draw Valley Rafters: Draw the valley rafters from the intersection of the two roof planes down to the eaves. These should also be at a 45-degree angle where the slopes meet.
Step 5: Add Common Rafters
Determine Rafter Spacing: Decide the spacing for common rafters based on building codes (e.g., 16 inches or 24 inches apart).
Draw Common Rafters: Draw lines from the ridge to the eaves to represent the common rafters. Ensure they are evenly spaced and correctly positioned.
Step 6: Add Jack Rafters
Determine Jack Rafter Placement: Identify the positions of the jack rafters (shorter rafters that span from a hip rafter to the eaves or from a valley rafter to the ridge).
Draw Jack Rafters: Draw the jack rafters from the hip rafters to the eaves and from the valleys to the ridge, ensuring they are evenly spaced and aligned with the common rafters.
Step 7: Draw Purlins and Facia Board
Add Purlins: Draw horizontal purlins that run perpendicular to the rafters, providing additional support.
Draw Facia Board: Represent the facia board along the edge of the roof to complete the roof outline.
Step 8: Dimensioning and Labeling
Add Dimension Lines: Place dimension lines outside the drawing to indicate the lengths and spacing of rafters, ridges, and other elements.
Label Key Elements: Clearly label all parts of the roof framing plan, including rafters, purlins, ridge member, hips, valleys, and facia board.
Step 9: Review and Refine the Plan
Check for Accuracy: Review the entire plan for accuracy in measurements, placements, and labeling.
Ensure Clarity: Make sure all lines and labels are clear and legible, ensuring the plan can be easily interpreted.
Key Elements of a Working Roof Framing Plan
Wall Outline: Accurate representation of the building’s wall outline.
Rafters: Proper placement of common rafters, jack rafters, hip rafters, and valley rafters.
Purlins: Horizontal supports that run perpendicular to the rafters.
Ridge Member: The horizontal peak of the roof.
Facia Board: The board running along the edge of the roof.
Labels: Clear labeling of all components.
Dimensions: Accurate dimensioning of all elements based on the chosen scale.
Example of a Roof Framing Plan
