ВИДЫ ФУНДАМЕНТОВ, ПРИМЕНЯЕМЫЕ В СТРОИТЕЛЬСТВЕ

The foundation of a house is a somewhat invisible and sometimes ignored component of the building. Good foundation design and construction practice means not only insulating to save energy, but also providing effective structural design as well as moisture, termite, and radon control techniques where appropriate.

Factors affecting the choice of foundation type and construction system include site conditions, overall building design, the climate, and local market preferences as well as construction costs. These factors are discussed below.

Site Conditions. The topography, water table location, presence of radon, soil type, and depth of bedrock can all affect the choice of a foundation type.

Overall Building Design. The foundation type and construction system are chosen in part because of appearance factors. Although it is not usually a major aesthetic element, the foundation at the base of a building can be raised above the ground plane, so the foundation wall materials can affect the overall appearance. A building with a slab-on-grade foundation has little visible foundation; however, the foundation wall of a crawl space or basement can vary considerably from almost no exposure to full exposure above grade.

Climate. The preference of foundation type varies with climatic region, although examples of most types can generally be found in any given region. One of the principal factors behind foundation preference is the impact of frost depth on foundation design. In a southern climate the incremental first cost of creating a basement is greater when compared with a slab-on-grade with no significant required footing depth. Buildings with very shallow foundations can be used in cold climates if they are insulated properly.

Local Market Preferences and Construction Costs. The foundation type and construction system are also chosen based on cost and market factors that vary regionally or even locally. These costs reflect local material and labor costs as well as the availability of certain materials and the preferences of local contractors. More subjective factors that influence a designer’s choice of foundation type and construction system are the expectations and preferences of individual clients and the home-buying public. These more subjective market factors and regional preferences tend to increase the availability of materials and contractors for the preferred systems, which in turn makes these systems more cost-effective choices.

21 Topics for projects and presentations:

Rain does not fall on the roof alone. (Proverb)

“Compromise makes a good umbrella but a poor roof.” (James Russell Lowell)

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

READING

4 a) Transcribe the following words:

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 stablein most weather and its slope disposes of rainwater quickly. Additionally, the space enclosedby 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 Figure. 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):