2. 12
Chapter
Roof Framing

3. Objectives List and describe the various types of roofs.
Identify the parts of a roof frame.
Define the terms slope and pitch.
Use a framing square, speed square, and rafter tables.
Lay out common rafters.

4. Objectives (Cont.) Describe the layout and erection of a gable roof.
Find the length of a hip rafter.
Explain the design and erection of trusses.
Describe the procedure for sheathing a roof.
Estimate roofing materials.

5. Roof Frames Provide base to which roofing materials will be attached
Must be strong and rigid
Can add distinctive and decorative character to structure
Both live loads and dead loads must be considered in roof design

6. Roof Types Gable roof Hip roof Gambrel roof Flat roof Shed roof
Mansard roof

7. Framing Systems Two basic systems used in framing roofs
Conventional, stick-built rafters
Truss rafters
Rafters are framing members that run from peak to wall plates
Roof trusses are prefabricated assemblies

8. Roof Supports Supports depend on type of rafter design Outside walls
Ceiling joists (beams that hold ceiling materials)
Interior bearing walls (partitions that support structures above)

9. Parts of Roof Frame Common rafters Hip rafters Valley rafters
Hip jacks
Valley jacks
Cripple jacks

10. Roof Frame in Plan View

11. Layout Terms and Principles
When two sides of right triangle are known, third side can be calculated: H2 = A2 + B2
Rafter is like hypotenuse of right triangle

12. Slope and Pitch Slope refers to incline of roof
Slope is given as “x inches-in-12”
Pitch is technically ratio of rise to span (twice run)
4-in-12 roof has pitch of 1/6 (4/24)
Pitch is also used to mean same as slope
It is simpler to call out rise and run: 5-in-12

13. Unit Measurements Framing square is basic layout tool for roof framing
Divisions called units are used to make rafter layout
Stair gauges can be attached to square to save slope on square

14. Framing Plans Roof framing information found in plans
Rise and run of roof
Required overhang
Subfascia and type of fascia
Type of ridge
Other information for roof construction

15. Rafter Sizes
Use building codes to select size of rafters

16. Code Note IRC includes rafter span tables for
Roof live load of 20 psf or ground snow load of 30 psf, 50 psf, or 70 psf
Ceiling not attached to or attached to rafters
Dead load of 10 psf or 20 psf
Rafter spacing of 12″, 16″, 19.2″, or 24″
Wood species and grade
Nominal rafter size: 2 × 4, 2 × 6, 2 × 8, 2 × 10, or 2 × 12

17. Laying Out Common Rafters
Rafters can be laid out using
Step-off method
Rafter table on framing square
Construction calculator
First lay out, check, and cut pattern rafter
Use pattern to mark other rafters of same size and type

18. Step-off Method

19. Rafter Table Table is on face side of square
Find line length of rafter from center of ridge to outside of plate
Add overhang and subtract half thickness of ridge board from length

20. Speed Square Used to find rafter lengths and determine angle of cuts
Is smaller and easier to carry than framing square
Larger version is called rafter square
Macklanburg-Duncan

21. Erecting Gable Roofs Lay out rafter spacing
Attach ridge to several rafters on one side
Raise and support assembly while rafters are nailed to plate
Install rafters on opposite side

22. Gable End Frame
Should be assembled after rafters and ridge have been installed
Consists of vertical studs running from top plate of bearing walls to end rafters
Should be well braced before installing ridge board and rafters

23. Hip and Valley Rafters
Hip rafters support intersection of two roof surfaces slanting upward
Use common rafters to calculate length of hip rafter, including overhang
Valley rafters used where two pitched roofs meet to form inside corner

24. Hip Jack Rafters
Short rafters that run between wall plate and hip rafter
Same as common rafters except for length
Consistent change in length is common difference

25. Valley Jacks Start layout at building line and move toward ridge
Use common rafter pattern
Extend plumb cut of bird’s mouth to top edge

26. Erecting Jack Rafters Assemble cut rafters into roof frame
Erect rafters in opposing pairs
Straighten any bowed rafters
Fasten fascia board to rafter or truss tails

27. Special Problems
To support ridge of narrow roof section, valley rafter is run to main ridge
Valley cripple jack is rafter framed between two valley rafters
Hip-valley cripple jacks run between hips and valleys

28. Roof Openings
May be required for chimneys, skylights, and other structures
First complete entire framework
Then, lay out and frame openings

29. Roof Anchorage
Outward thrust along top plate must be considered in framing design
End walls need extra support, especially for hip roofs
Stub ceiling joists and metal straps are used to reinforce roof

30. Collar Ties Tie together two rafters on opposite sides of roof
Provide bracing and stiffening to hold ridge and rafters together
Purlins may be used to provide extra support

31. Dormers Framed structures projecting above sloping roof surface
Shed dormers
Gable dormers
Normally contain vertical window units

32. Framing Flat Roofs Ceiling and roof members may be combined system
Most designs require overhang
Pueblo style
Flat roof supported by vigas
May have parapet walls

33. Gambrel Roof Like gable roof but has four slopes
Often used in two-story construction
Gives added living space with minimal outside wall framing

34. Mansard Roof Has two slopes with lower slope being steeper
Extends around all four sides of building
Second floor joists extend beyond first floor wall
Extension provides support for lower rafters
N. Mitchell/Shutterstock.com

35. Special Framing
Low-sloping roofs usually need support at several points

36. Roof Trusses Frames that carry roof and ceiling surfaces
Rest on exterior walls and span width of structure
W truss or Fink truss
King post truss
Scissors truss

37. Roof Truss Construction
In trusses, joint slippage must be at minimum
Special connectors hold joints firmly

38. Bracing Truss Rafters Proper bracing for trusses is essential
Temporary bracing during construction
Inside permanent bracing
Clip keeps truss in alignment and allows vertical movement of lower truss chord

39. Roof Sheathing Provides nailing base for roof covering
Adds strength and rigidity to roof frame
Made from plywood or OSB
Skip sheathing should be used for wood shingles, metal sheets, or metal tile

40. Structural Panels Ideal for roof sheathing Can be rapidly installed
Hold nails well
Resist swelling and shrinkage
May be slid up ladders or placed on special racks

41. Installing Sheathing Start at eaves and work up toward ridge
Use temporary fasteners at corners to keep panels square
Lay down rows of panels from edge to edge of roof
Stagger end joints between rows of panels
Trim extra overhang at ends of gable roof

42. Panel Clips Used to strengthen roof sheathing panels between rafters
Eliminate need for blocking on long truss or rafter spans
Two clips should be used where supports are 48″ O.C.
The Panel Clip Co.

43. Safety Note
Work from scaffold to install fascia and lay first row of roof sheathing
Never place tools, materials, or debris where they can slide off roof
Follow OSHA rules that require fall protection, guardrails on scaffolding, and hard hats

44. Estimating Materials Number of rafters required for plain gable roof
Multiply length of building by 3/4 for spacing 16″ O.C.
Round up and add one more
Double figure to include other side of roof
For complex roof frames, work from complete framing plan

45. Model and Small-Scale Construction
Working with models requires much time
Often best to construct only part of building
Small buildings, such as storage sheds, can be sold to recover cost of materials
Scale of 1 1/2″ = 1′-0″ usually makes it possible to apply regular framing procedures