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THE BUILDING PROCESS

  • Overview
  • Roof Coverings

Overview

This section is about roofs and roofing – the materials and products, methods and certain criteria which are used in the construction of these elements. A more specific purpose is to draw the attention of readers to features and functions of different types of roofs and roofing and the overall cost considerations in choosing different types. Notwithstanding certain roofs suit only certain designs. With an age of diversity in the building Industry and the abundant choice of design and materials, one tendency has become very clear; the increasing complexity of the geometry of buildings, and more especially of roofs. It is therefore simple to deduce that defects increase in direct proportion to this increase in complexity of geometry of the surfaces of buildings; i.e. at the intersections of different planes and materials.

Added to this is the increasing lack of properly skilled artisans in erecting roof structures and the fi tment of the desired roof coverings, associated fittings and accessories; highlighting the need for taking extra care in both design and construction, when it comes to roofing and not only making decisions based on price alone. One must consider that a roof has numerous functions other than aesthetics that need to be taken into account in the design and costing analysis;
  • Protection from sun, wind and rain.
  • Strength and stability
  • Durability
  • Control of heat loss – insulation
  • Prevention of condensation
  • Acoustics - exclusion and prevention of noise
  • Fire protection and prevention
  • Provision of day lighting; where appropriate.

There is an absolute requirement in roofi ng to prevent water reaching the interior of a building, in contrast with some of the other functional requirements where some shortfall may be tolerable. Again; highlighting the need for taking care in design and the construction/ erection of roofs and roofi ng to ensure water penetration into the interior of the building is avoided.

Two kinds of rainfall intensity need to be considered;
  • Rain falling vertically
  • Rain driven by wind

Both categories contribute to the total quantities of rainwater needing disposal, but the second category particularly affects the weather tightness of lapped roofing, such as tiles and slates, and even the direction and extent of lap of larger sheets; with many manufacturers recommending the use of underlays, fixing of tiles etc. in these applications.

One must remember that rain falling while the wind is blowing affects pitched roofs more than flat (and walls even more so), it is therefore important to consider ones geographical location, associated weather patterns and not only your desired roofing requirements.

Roof Coverings

Clay Roof Tiles
Burned clay was the commonly used material in Ancient times in manufacturing of roof tiles. Used for centuries and still used, however this type of tile is more expensive than the more common concrete tile.

Clay roof tiles enhance warmth and character to a building with permanent colour which weather and age over time, but never fade. Clay roof tiles are natural and durable which elegantly enhances the appearance of roofs, not only withstanding the elements, but actually improving with age from exposure.

Clay roof tiles are available in the ever-popular Broseley, Constantia & Cordova as well as the cost effective Portuguese and Marseilles. They are available from various different manufacturers in South Africa, in a variety of colours like terracotta and multi flashed colours. Various bonds are used when laying different types of clay tiles, from; straight bond or mock interlocking, broken bond, flat and semicircular over under (the over-tile and under-tile are of roughly the same shape, the under-tile being larger; these tiles form a beautiful roof which is flexible in both sidelap and headlap).

Concrete Roof Tiles
Concrete roof tiles are manufactured in an extensive range of profiles, colours and finishes (finishes will vary from one manufacturer to another) which enhance the visual appearance of any roof and provide designers with a wide scope for expression. Surface finishes for tiles are categorized in accordance with SABS specifications.

All surface coatings are applied under factory controlled conditions. Concrete roof tiles manufactured by members of the Concrete Manufacturers Association meet the requirements of SABS 542-1990 Standard specification for concrete roof tiles. They are manufactured in accordance with the SABS ISO 9002 Quality Management System

Pressed Metal Roof Tiles
Pressed metal roof tiles are strong, light weight; which significantly reduces the quantity of timber required in the support structure and provides easy installation. They allow for ease of delivery and don’t require large trucks to transport them, making this a popular roof covering in remote lying areas. A further advantage being steel-based, no breakages occur during transit or storage on site.

Metal roof tiles come in different profiles and finished with either a standard acrylic coating or a textured coating and available in various colours and are also manufactured from different materials.

Tiles are complemented by a full range of accessories such as ridges, hips, gable trims, bargeboard covers and flashings. Due to their lightweight attributes, tiles are the ideal application in the re-roofing market where they can be laid over the existing roof without removing the old roofing material.

Slates can be described as any rectangular sheet of roofing material, whether of natural slate, stone, cast stone, fibre cement, or metal.

Fibre cement
  • The Nutec roofing range offers designers and specifi er’s freedom and flexibility when functional, aesthetic and cost criteria need to be met.
  • The Nutec Roofing Range is complemented with all necessary fi noshing components including ridge caps, flashing and fixing accessories.
  • Nutec roof slates are designed for a minimum roof pitch of 17,5°
  • In high wind arrears the slates may no longer provide a waterproof covering and a waterproof underlay must be installed. For areas where design wind pressure exceeds 1,2Kpa Everite should be contacted for specific fixing recommendations.
  • It is important to be aware of the fact that any distortion or unevenness in the roof structure and battens will reflect in the final appearance of the application. Time spent to ensure that the structure and battens are accurate and sound is therefore a small investment in the process of achieving an excellent result.

Natural Slate
Slate is commonly described as a dark grey natural stone made up of many thin layers which can be split (riven) into thin sheets, then cut to size to create tiles.

Other colours are available in roofing slates and not just the traditional dark grey or silver blue as it is known; below are the commonly used colours in roofing.
Silver Blue: The colour ranges from silver to grey to almost black, and may occasionally contain faint tints of yellow or gold.
West Country: This is a silver blue based slate with rings, circles or spots of red, brown, silver, white, orange, yellow and very occasionally green, with one or more of these colours present on each tile.
Multi colour: This is a silver blue based slate with subdued to bright colouring on at least 20% of the surface area. The colour varies from reds, brown, orange, yellows and even greens, or any combination thereof.
Sheeting
Roof sheeting comes in various different profiles, e.g. corrugated, IBR and folded steel. Manufactured from numerous different types of material to suit specific applications, all having certain advantages and unique properties; with metal sheeting being the most commonly used.

Organic Fibre
Onduline is an extremely tough lightweight corrugated roofi ng and wall cladding material manufactured from bitumen-saturated organic fi bres under intense pressure and heat. It is fl exible, economical and virtually indestructible. It provides a high degree of weather protection and thermal insulation - even in the most extreme climatic conditions.

Originally developed in Europe over 50 years ago, Onduline is now extensively used in agricultural, light industrial and domestic applications in over 100 countries from the tropics to the artic circle. Onduline offers many advantages over other roofi ng and wallcladding materials.
  • Needs virtually no maintenance
  • It has high insulation and sound absorbency values
  • Cannot rust or become brittle
  • Rot and fungi resistant.
  • It is colourfast and resists most chemicals and corrosion.
  • It is impact resistant and easy to handle.

Onduline is probably the most flexible, versatile and economicalroofi ng and cladding material in the world.

Types, colours and sizes Onduline simplifies the work of the designer, architect and specifier as there is just one convenient standard size of sheet to work with. It is further simplified by its easy cutting and fixing characteristics. Onduline can be cut with an ordinary hand or power saw and is fi xed using corrosion resistant PE headed or safe top nails. Onduline is manufactured in the following pre-pigmented (PP) colours;

Fibre cement
Fibre-cement technology was developed at the end of the 18th century by an Austrian, Ludwick Hatschek. Products are made of Portland cement, refined sand and specially treated cellulose fibres.

The mould ability, strength and durability of fibre-cement makes it a perfect material for the manufacture of a wide range of building materials.

Fibre cement roof sheeting is available in two basic profi les and has been used in the south African building Industry for roofing and side cladding for decades.

The Victorian sheet is a popular profile and it has been designed to recreate the appearance and character of a traditional Victorian style roof. And is particularly suitable for coastal areas where corrosive conditions prevent the use of many other products.

Metal
Metal Roof sheeting is available in a wide variety of profi les, thicknesses and types of material and coatings.

Usually all roof sheeting materials are manufactured from hot-dipped galvanized steel and fall within internationally accepted specifications and tolerances. HH Robertson, established in 1958 was the first manufacturer of roof sheeting in South Africa.

Other types of material are manufactured like Supergalm which is an aluminium zinc alloy coated steel and Zincalume® a composite of aluminium and zinc. Typical types of material include; Commercial quality, high tensile and econogalv. Typical types of coatings include Chromadek. There are a large variety of sheeting materials and profiles designed for larger type commercial buildings like shopping centres and industrial buildings which require specific properties that suit this type of application. These are quite different to what is required for the smaller type building and the residential housing market; although these types of materials and profiles can be used in residential applications. e.g. Brownbuilt.
 
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