edt 300 - cabin design project - roofs1 weekend cabin retreat project roofs sacramento city college...

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.


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.


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.


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.


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.


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.


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.


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.


Winged GableWinged Gable

The winged gable is a variation on the gable roof.

Ridge peaks are extended to form a point.


Dutch HipDutch Hip

The dutch hip is a combined gable and hip configuration.


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.


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.


Curved Plate RoofCurved Plate Roof

Similar to Folded Plate roof. Limited residential application. Some use in prefabricated

modules.


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.

EDT 300 - Cabin Design Project - Roofs

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Traditional Frame Roof ConstructionTraditional Frame Roof Construction


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.


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.


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.


RaftersRafters

Terms that must be understood before calculating rafter dimensions and roof pitch are: Rise. Run. Span.


TerminologyTerminology

Rise - the vertical distance measured from the top of the wall plate to the underside of the rafters.



Run - one-half of the distance of the clear span.



Clear Span - is the horizontal distance from the inside of one stud wall to the inside of the opposite stud wall.


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.


Roof SlopeRoof Slope

When designing a roof, use a standard roof pitch.

3 in 12. 4 in 12. 5 in 12. 6 in 12.


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.


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.


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.


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.


CorniceCornice

Three types in residential construction: Open cornice Box cornice Close cornice


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.


Three Types of Box CorniceThree Types of Box Cornice

Narrow Box. Wide Box with Lookouts. Wide Box without Lookouts.


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.


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.


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.


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.


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.


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.


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.



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.



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.



W-type truss King-post truss Scissors truss are commonly used in residential

construction.



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.


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.


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.


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.


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.


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.


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.


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.


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


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


RoofingRoofing

Factors affecting choice of material: cost local codes roof pitch design individual preference

edt 300 - cabin design project - roofs1 weekend cabin retreat project roofs sacramento city college...

Documents

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