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EDT 300 - Cabin Design Project - Roofs
1
Weekend Cabin Retreat ProjectWeekend Cabin Retreat ProjectRoofsRoofs
Sacramento City CollegeEDT 300
Kenneth Fitzpatrick, P.E.
2 EDT 300 - Cabin Design Project - Roofs
Types of RoofsTypes of Roofs
The appearance of a house is affected greatly by the roof lines and material.
The roof should compliment the structure.
3 EDT 300 - Cabin Design Project - Roofs
4 EDT 300 - Cabin Design Project - Roofs
5 EDT 300 - Cabin Design Project - Roofs
Gable Roof Gable Roof
The gable roof is very popular. Easy to build. Sheds water well. Provides for ventilation. Can be used on a variety of house
designs.
6 EDT 300 - Cabin Design Project - Roofs
7 EDT 300 - Cabin Design Project - Roofs
Hip Roof Hip Roof
The hip roof is slightly more difficult to build than a gable roof.
The hip roof is a very popular choice.
Does not provide for ventilation as well as gable roof.
Increased chance of leaks because of hips and valleys.
8 EDT 300 - Cabin Design Project - Roofs
9 EDT 300 - Cabin Design Project - Roofs
Flat Roof Flat Roof
The flat roof is the most economical roof to construct.
Doesn’t add much to the appearance of the house.
Requires “built-up” or membrane roof covering instead of conventional shingles. A built-up roof consists of layers of roofing
felt and tar. Usually pitched about 1/8” to 1/2”
to provide for drainage.
10 EDT 300 - Cabin Design Project - Roofs
Flat Roof Flat Roof
The flat roof is popular in warmer areas of the country where wide overhangs are desirable for shade and where little or no snow falls.
11 EDT 300 - Cabin Design Project - Roofs
12 EDT 300 - Cabin Design Project - Roofs
Shed Roof Shed Roof
The shed roof is similar to flat roof but has more pitch.
Frequently used for additions to existing buildings.
A built-up roof is often required.
Pitch must be 3:12 to use shingles.
13 EDT 300 - Cabin Design Project - Roofs
14 EDT 300 - Cabin Design Project - Roofs
Butterfly Roof Butterfly Roof
The butterfly roof has not been used widely in the past.
Provides plenty of light and ventilation.
Drainage is the problem. Flashings must extend far up the
roof to prevent leaks.
15 EDT 300 - Cabin Design Project - Roofs
16 EDT 300 - Cabin Design Project - Roofs
Gambrel RoofGambrel Roof
The gambrel roof is sometimes called a “barn roof”.
It has been used extensively for barns.
Provides the additional headroom required for the “Dutch colonial” building style.
17 EDT 300 - Cabin Design Project - Roofs
18 EDT 300 - Cabin Design Project - Roofs
Winged GableWinged Gable
The winged gable is a variation on the gable roof.
Ridge peaks are extended to form a point.
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20 EDT 300 - Cabin Design Project - Roofs
Dutch HipDutch Hip
The dutch hip is a combined gable and hip configuration.
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22 EDT 300 - Cabin Design Project - Roofs
Mansard Roof Mansard Roof
The mansard roof has not been popular for several years.
Is returning to popularity. Is a French design. Is more difficult to construct than
hip or gable.
23 EDT 300 - Cabin Design Project - Roofs
24 EDT 300 - Cabin Design Project - Roofs
A-Frame RoofA-Frame Roof
The A-frame is a combined wall and roof.
Originally used for cottages. Now is used for homes, churches,
and other structures.
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26 EDT 300 - Cabin Design Project - Roofs
Curved Plate RoofCurved Plate Roof
Similar to Folded Plate roof. Limited residential application. Some use in prefabricated
modules.
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28 EDT 300 - Cabin Design Project - Roofs
Folded Plate Roof Folded Plate Roof
The Folded Plate Roof is a contemporary design.
It is finding some limited application in residential construction.
Quite popular for motels and small commercial buildings.
Many modular, prefabricated units have this type of roof.
29 EDT 300 - Cabin Design Project - Roofs
EDT 300 - Cabin Design Project - Roofs
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Traditional Frame Roof ConstructionTraditional Frame Roof Construction
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RaftersRafters
Roof covering material is supported by roof framing.
The framing must be strong and rigid.
Roof framing consists of several distinct structural elements.
The first and most basic of these elements is the rafter.
32 EDT 300 - Cabin Design Project - Roofs
RaftersRafters
Common rafters are perpendicular to the top wall plate.
They extend from the plate or beyond to the ridge of the roof.
Note that several types of rafters other than common rafters are identified.
33 EDT 300 - Cabin Design Project - Roofs
34 EDT 300 - Cabin Design Project - Roofs
RaftersRafters
Rafters are cut to the proper dimensions by locating the ridge cut, seat cut, plumb cuts, and tail cut.
The precise layout of these cuts is determined by The slope or pitch of the roof. The inside width or clear span of the
building.
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36 EDT 300 - Cabin Design Project - Roofs
RaftersRafters
Terms that must be understood before calculating rafter dimensions and roof pitch are: Rise. Run. Span.
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TerminologyTerminology
Rise - the vertical distance measured from the top of the wall plate to the underside of the rafters.
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39 EDT 300 - Cabin Design Project - Roofs
TerminologyTerminology
Run - one-half of the distance of the clear span.
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41 EDT 300 - Cabin Design Project - Roofs
TerminologyTerminology
Clear Span - is the horizontal distance from the inside of one stud wall to the inside of the opposite stud wall.
42 EDT 300 - Cabin Design Project - Roofs
43 EDT 300 - Cabin Design Project - Roofs
Roof SlopeRoof Slope
Roof slope may be indicated on the drawings by: A slope ratio diagram A fractional pitch indicator An angular dimension.
The angular dimension method is seldom used
It is difficult to measure as accurately as either of the other methods.
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Roof SlopeRoof Slope
When designing a roof, use a standard roof pitch.
3 in 12. 4 in 12. 5 in 12. 6 in 12.
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RaftersRafters
Select rafters based on The distance to be spanned. The spacing of the rafters. The weight to be supported.
Rafters for low-slope roofs may also serve as ceiling joists.
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Roof Weights Per Square FootRoof Weights Per Square Foot
A “light roof” is one that weighs less than 4 lbs per square foot.
Examples: Cedar shake roof. Composition roof. Metal roof.
47 EDT 300 - Cabin Design Project - Roofs
Roof Weights Per Square FootRoof Weights Per Square Foot
A “heavy roof” is one that weighs more than than 4 lbs per square foot.
Examples Slate. Clay tile. Concrete tile.
48 EDT 300 - Cabin Design Project - Roofs
49 EDT 300 - Cabin Design Project - Roofs
50 EDT 300 - Cabin Design Project - Roofs
51 EDT 300 - Cabin Design Project - Roofs
CorniceCornice
The cornice is the overhang of the roof at the eaves line.
It forms a connection between the roof and the side walls.
In a gable roof, the cornice is formed around two sides of the building
In a hip or flat roof, the cornice is formed around all four sides of the building.
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53 EDT 300 - Cabin Design Project - Roofs
CorniceCornice
Three types in residential construction: Open cornice Box cornice Close cornice
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Open CorniceOpen Cornice
The Open Cornice may be used with: Exposed beam construction. Contemporary designs Rustic designs
Rafter ends are exposed and are usually tapered or curved to prevent a bulky appearance.
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56 EDT 300 - Cabin Design Project - Roofs
Three Types of Box CorniceThree Types of Box Cornice
Narrow Box. Wide Box with Lookouts. Wide Box without Lookouts.
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Narrow Box CorniceNarrow Box Cornice
Usually between 6” and 12” wide. The soffit board is nailed directly to
the bottom side of the rafters. Usually used for Cape Cod or
colonial homes.
58 EDT 300 - Cabin Design Project - Roofs
59 EDT 300 - Cabin Design Project - Roofs
Wide Box Cornice with LookoutsWide Box Cornice with Lookouts
Is usually between 6” and 12” wide.
Requires additional support members called “lookouts” for fastening the soffit
The soffit board is nailed directly to the bottom side of the rafters.
60 EDT 300 - Cabin Design Project - Roofs
61 EDT 300 - Cabin Design Project - Roofs
Wide Box Cornice without LookoutsWide Box Cornice without Lookouts
Has a sloped soffit The soffit material is nailed tot he
underside of the rafters. Frequently used where overhangs
are very wide.
62 EDT 300 - Cabin Design Project - Roofs
63 EDT 300 - Cabin Design Project - Roofs
Close Cornice Close Cornice
Is one in which the rafter does not project beyond the wall.
The roof is terminated by a frieze board and molding.
64 EDT 300 - Cabin Design Project - Roofs
65 EDT 300 - Cabin Design Project - Roofs
Rake or Gable EndRake or Gable End
Is the extension of a gable roof beyond the end wall of the house.
The overhang should be about the same size as the cornice.
If a close cornice is used, a close rake should be used.
66 EDT 300 - Cabin Design Project - Roofs
Rake or Gable EndRake or Gable End
Wide overhangs provide side wall protection and less frequent painting.
In California, wide overhangs provide shading from hot summer sun.
67 EDT 300 - Cabin Design Project - Roofs
68 EDT 300 - Cabin Design Project - Roofs
Roof TrussesRoof Trusses
Roof trusses are an assembly of members that form a rigid framework of triangular shapes.
They permit wide unsupported spans with a minimum amount of material.
69 EDT 300 - Cabin Design Project - Roofs
70 EDT 300 - Cabin Design Project - Roofs
71 EDT 300 - Cabin Design Project - Roofs
72 EDT 300 - Cabin Design Project - Roofs
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77 EDT 300 - Cabin Design Project - Roofs
78 EDT 300 - Cabin Design Project - Roofs
Roof TrussesRoof Trusses
Lightweight wood roof trusses are designed to span distances of 20 to 32 feet.
Many times trusses are less expensive than conventional framing.
Time and expense is saved.
79 EDT 300 - Cabin Design Project - Roofs
Roof TrussesRoof Trusses
Prefab trusses for standard widths are readily available.
Custom trusses for non-standard dimensions are factory produced.
Most trusses are made from 2 x 4 lumber.
2 x 6 may be used for wider spans and heavier loads.
80 EDT 300 - Cabin Design Project - Roofs
Roof TrussesRoof Trusses
W-type truss King-post truss Scissors truss are commonly used in residential
construction.
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Roof TrussesRoof Trusses
Most are designed to be installed at 24” on center.
Ceiling materials are nailed directly to the bottom of the truss.
Information required to make Span Roof pitch Spacing of the trusses Anticipated roof load.
82 EDT 300 - Cabin Design Project - Roofs
VentilationVentilation
Adequate attic ventilation is critical.
Moisture will form on the underside of the roof sheathing and damage will result.
A well-ventilated attic will help to cool the house in the summer.
83 EDT 300 - Cabin Design Project - Roofs
VentilationVentilation
Ventilation is usually achieved by louvered openings on the gable end.
Ridge ventilators are also available.
The total are of the ventilation openings should be 1/300 of the ceiling area.
1200 sq ft. Ventilation openings at least 4 sq ft.
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85 EDT 300 - Cabin Design Project - Roofs
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92 EDT 300 - Cabin Design Project - Roofs
FlashingFlashing
Flashing should be used where the roof comes in contact with a wood or
masonry wall. At a chimney. At a roof valley.
Common flashing materials: Aluminum Copper Galvanized sheet steel.
93 EDT 300 - Cabin Design Project - Roofs
FlashingFlashing
The flashing is placed under the roofing material a sufficient distance to prevent the penetration of water.
Roof valleys flash with metal or two thicknesses or roll
type roofing. Asphalt roofing mastic is used
under the shingles adjacent to the valley to aid in waterproofing this area.
94 EDT 300 - Cabin Design Project - Roofs
95 EDT 300 - Cabin Design Project - Roofs
FlashingFlashing
A small metal edging is normally used at the gable and eave line to act as a drip edge
Its purpose is to prevent water from entering behind the shingles and to protect the fascia boards.
96 EDT 300 - Cabin Design Project - Roofs
97 EDT 300 - Cabin Design Project - Roofs
Gutters and DownspoutsGutters and Downspouts
Gutters collect the water and prevent it from running directly off the eaves and splattering the house.
Downspouts are the pipe to channel the roof water to the ground.
Copper, vinyl, aluminum and galvanized sheet steel are common materials.
98 EDT 300 - Cabin Design Project - Roofs
99 EDT 300 - Cabin Design Project - Roofs
100 EDT 300 - Cabin Design Project - Roofs
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102 EDT 300 - Cabin Design Project - Roofs
103 EDT 300 - Cabin Design Project - Roofs
Roof Sheathing and RoofingRoof Sheathing and Roofing
Sheathing is placed over rafters Supports the roofing material May be
planks individual boards plywood
Plywood is most common.
104 EDT 300 - Cabin Design Project - Roofs
Roof Sheathing and RoofingRoof Sheathing and Roofing
Sheathing thickness varies with the spacing of the rafters and supporting beams.
Sheets are laid with grain perpendicular to the rafter
Joints are staggered
105 EDT 300 - Cabin Design Project - Roofs
RoofingRoofing
Common materials: asphalt singles wood shingles tile slate roll roofing copper, aluminum and galvanized sheet
steel layers of felt and tar rubber membrane roofing
106 EDT 300 - Cabin Design Project - Roofs
RoofingRoofing
Factors affecting choice of material: cost local codes roof pitch design individual preference
107 EDT 300 - Cabin Design Project - Roofs
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