Roofing and Trusses

Question 1

Define Roof

Answer 1

A protective covering that covers or forms the top of a building

Question 2

Functional Requirements

Answer 2

1. Strength
2. Stability
3. Durability
4. Weather Resistance
5. Fire Resistance
6. Thermal Insulation
7. Sound Insulation

Question 3

Strength

Answer 3

Depends on the characteristics of the materials used, and on the formation of the materials

eg: Horizontal platform, triangular framework

Question 4

Stability

Answer 4

• Joists and beams need to be adequately thick to support roof
• Mindful of the depth of the frames at mid-span, short-span, and wide-span
• Should resist dead-loads, and be properly supported by the walls of the building to distribute imposed loads
• Be able to resist strong winds

Question 5

Durability

Answer 5

Persistent penetration of water into the roof structure may cause decay of timber, corrosion of steel or disintegration of concrete.

Dry rot, Deterioration, Disintegration, Corrosion

Question 6

Weather Resistance

Answer 6

• Resistance provided by rooof coverings
• To prevent any water from entering internal spaces
• Resistance to condentsation by being adequately ventilated
• Ability to properly drain rain off

Question 7

Fire Resistance

Answer 7

• Degree of fire resistance needed depends on the proximity of other buildings and the nature of the building being covered by roof
• Prevention of spread of fire to adjacent buildings
• Prevention of the early collapse of the roof

Question 8

Thermal Insulation

Answer 8

• Most roof materials are poor heat insulators
• Should resist solar heat gains
• Ceilings provided to separate roof space and usable rooms
• Provisions should be made for any movements caused by variation in thermal temperatures and humidity

Question 9

Sound Insulation

Answer 9

• Provide resistance to airborne sounds and sounds from loud surroundings
• Mass and contininity of roofing is major factor in sound-proofing
• Extra considerations for speciality buidlings like concert halls

Solid Concrete, Mineral Fibre Slabs, Thick Boards, Batts

Question 10

Types of Roofs

Answer 10

1. Flat
2. Lean-To
3. Pitched/Gable
4. Mansard
5. Hipped
6. Pyramid
7. Gambrel

Question 11

Gable

Answer 11

Upper part of an external wall where the slopes of the roof give the gable a triangualar shape

Question 12

Hip

Answer 12

The angled meeting of two sloping roof structures which forms an external angle

Question 13

Valley

Answer 13

The meeting of two sloping roof surfaces which forms an internal angle inside a complex roof

Question 14

Wall Plate

Answer 14

Horizontal timbers along the top of a wall which the roof beams are attached to

Question 15

Ceiling Joists

Answer 15

Horizontal timbers which act as a collar and provide a fixing for the ceiling layer

Question 16

Rafters

Answer 16

Sloping roof timbers which run down from the ridge to the eaves and transfer loads to the wall plate

Question 17

Purlins

Answer 17

Horizontal roof beams that link and brace the rafters

Question 18

Ridge Board

Answer 18

A horizontal board set on the edge of a peak of a pitched roof where the rafters or timbers meet

Question 19

Collar

Answer 19

A horizontal timber in tension which acts as a tie between rafters on opposite sides of a pitched roof (higher than a strut)

Question 20

Struts

Answer 20

Timbers in compression between purlins and collars in a roof structure or truss

Question 21

Eaves

Answer 21

The bottom edge of a roof that overhangs, and the area beneath the overhang

Question 22

Soffit

Answer 22

Horizontal board fixed to the underside of rafters to overhangning eaves

Question 23

Fascia

Answer 23

Vertical board fixed to the ends of the rafters

Question 24

Roof Coverings

Answer 24

1. Thatch
2. Plain tile
3. Concrete plain tiles
4. Slate tile
5. Interlocking tiles
6. Pan tiles
7. Sheet metal
8. Asphalt (Flat Roofs)

Question 25

Sheet Roof Fittings

Answer 25

1. Close Fitting Ridge Piece
2. Barge Board
3. Eaves Filler Piece
4. Eaves Closure Piece