3 Discuss the following:

• Write a paraphrase. • Say whether you agree or not, and why.

4 A) Transcribe the following words:

retain, ensure, weighted, storage, triangular, require, joists, corrugated, securely.

b)In what context do you think the following words and phrases will appear in the text?

• topmost part • interior cool • resisting fire • supporting structure • storage space • gable end • meet right angles • water-proof covering •corrugated sheets • galvanized steel ties• rafter

3. Read the text and check your answers:

ROOFS

A roof is the topmost part of a building. It is a covering constructed over the enclosed space to:

- keep out rain and wind;

- provide shade from the sun;

- keep the interior cool;

- retain heat in cool weather;

- ensure that the structure is properly weighted down.

Roofs should meet the following basic standards of performance: 1) allowing rainwater to flow freely away; 2) expanding and contracting without failure; 3) resisting fire adequately; 4) providing light and ventilation; 5) durability.

In this unit two types of roofs are considered: pitched roofs and flat roofs.

A pitched roof is often a popular choice. The main supporting structure is timber, which is easy to work and transport. A pitched roof is stable in most weather and its slope disposes of rainwater quickly. Additionally, the space enclosed by the roof can add some extra living or storage space.

In simple roof construction these types of roof are usually found:

Gable roof In this type of roof the ends of the roof enclose the end walls. The triangular wall between the roof verges is called the gable end.
Hipped roof A hipped roof is formed when two roof slopes meet right angles.
Lean-to roof This roof has a single pitch that rests against a higher wall.
Mono-pitch roof This roof has a pitch in one direction. The ridge does not rest against anything.

Three parts of a pitched roof affect the structural design: span; pitch; roof covering.

The span is the distance between the masonry structures that support the roof. The structure of the roof becomes more complex as the span increases.

The pitch is the angle of the slope of the roof measured from the horizontal. A steeper pitch needs more roof covering material, which increases the weight to be supported. The surface area affected by wind is also greater. The roof needs to be strong enough to allow for these factors.

The roof covering material varies from lightweight sheets that weigh 12 kg/m² to plain clay tiles that weigh 65 kg/m².

Flat roofs, which can be timber or reinforced concrete, are popular forms of roofing for houses. Their advantages are:

- they are very easy to put up;

- they can create extra usable space if they are accessible;

- they are easily maintained.

Their main disadvantages are that:

- they lose heat;

- they are not as weatherproof as pitched roofs;

- the finishes do not last as long as roof tiles.

The structure of a flat timber roof is shown in Fig. 9.2. and it requires: a deck or a slab; a method for disposing of rainwater; a watertight covering; some insulation.

Figure 9.2 Flat Timber Roof Structure

The joists span between the supporting walls and boarding is fixed over the joists to form a deck for the water-proof covering. Here the deck must have enough slope to get rid of rainwater. Slopes can be made by fixing strips of wood called firrings to the top of the joists.

Wind pressure can strip off tiles, lift overhanging eaves and verges and blow off corrugated sheets. If the roof covering is fixed very securely to the roof framework, then a strong wind could lift off the timbers of the roof structure.

This can be prevented by using galvanized steel ties every 1800 mm. They should be taken across the wallplate and down the wall for 600 mm and embedded in mortar joint. The ties can also be taken around the rafters to secure the roof structure against the lifting action of wind.

5. Read the text again and answer the questions that follow (1-8):

1. What are the purposes of roof construction?

2. There are five basic standards of performance, aren’t there? What are they?

3. How many types of roofs are considered in this unit? Name them.

4. How can you characterize types of roofs in simple roof construction?

5. What affects the structural design of a pitched roof? Describe these parts.

6. What are the advantages/ disadvantages of flat roofs?

7. What forms a deck for the water-proof covering?

8. Can you offer the ways how to cope with wind pressure?

Follow-up