Ответьте на вопросы к тексту. The structure of a flat roof is generally similar to that of a floor, but lighter

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ROOFS

The structure of a flat roof is generally similar to that of a floor, but lighter. In steel-framed buildings the roof materials most widely used are steel and concrete.

Metal roofing Galvanised steel sheet is widely used for externally insulated roofs. The sheets are fixed to the supporting beams by welding, bolts or blind rivets etc. The required depth of the section and the weight of the sheeting as a function of the total roof load, the span and the support conditions, single or two spans should be estimated. If the upper surface of the roof has to be constructed to a certain fall to help rainwater run-off, this should be achieved by an adequate sloping of the roof beams.

The steel sheet is in itself impervious to water vapour, but the longitudinal and transverse joints are not always watertight. Under normal internal and external conditions (internal relative humidity 65%, internal temperature + 20°C, outside temperature - 15°C), however, a vapour barrier is not required if full air-conditioning is not installed.

Concrete roof slabs Concrete roof slabs, laid in-situ or composed of precast concrete units and with or without composite action, are generally similar in construction to floor slabs. Such roofs are more particularly suitable in circumstances where relatively large loads have to be supported by the roof structure.

Lightweight concrete slabs, though possessing good thermal insulation capacity, must nevertheless be provided with additional insulating layers of adequate thickness to ensure that the temperature in the concrete always remains above the dew-point. Aerated concrete is very suitable as a lightweight covering, as are also various lightweight aggregate concretes. A fall for rainwater run-off from a concrete roof can also be obtained more economically by properly sloping the roof beams than by means of a screed.

Notes:

air-conditioning n. кондиционирование воздуха

blind rivet глухая заклёпка

fall n. зд. уклон

impervious adj. непроницаемый

sheeting n. обшивка

1. What is the difference between the structure of a flat roof and a floor?

2. What kinds of roofing are described in the text?

3. What should be esti­mated in construction of metal roofing?

4. What are the features which characterise metal roofing watertightness?

5. When is concrete roofing more suitable?

6. What kinds of concrete slabs are used for the purpose?

7. What must be done to achieve good thermal insulation of concrete roofing?

8. What must be done to avoid rainwater leakage (протечка) in a concrete roof?

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