Roof construction materials

Roof construction materials an article about the type of roof construction that consists of beams and an outer weatherproof skin, as found on most domestic architecture. Such roofs may take a number of different shapes and be constructed of and covered with a variety of materials.

A simple ridged roof consists of inclined rafters that rest on horizontal wall-plates on top of each wall. The top ends of the rafters meet at the horizontal ridge plate or ridge beam. Horizontal purlins are fixed to the rafters to support the roof covering. Heavier under purlin are used to support longer rafter spans. Tie beams or ceiling joists, are connected between the lower ends of opposite rafters to prevent them from spreading and forcing the walls apart. Collar beams or collar ties may be fixed higher up between opposite rafters for extra strength.

The rafters, tie beams and joists serve to transmit the weight of the roof to the walls of the building. There are a number of structural systems employed to facilitate this, including the use of wall-plates set at the top of the wall, hammer-beams, which spread the weight down the wall and create an equilibrium between outward and upward thrust, king posts which transfer the weight of the roof ridge, and various types of trusses.

In cyclone and hurricane prone areas the main engineering consideration is to hold the roof down during severe storms. Every component of the roof (as of course the rest of the structure) has to withstand the uplift forces of high wind speeds. This is not normally a problem in areas not prone to high wind.

Modern roofing technologies include the purpose-made steel hook bracket which is bolted to the truss with an M16 bolt. The bracket is bolted to an M16 bolt cast in situ, embedded 300 mm into the reinforced concrete block wall. This system is typically in place every 900 mm around perimeter.

Commercially available roofing materials

The weather proofing material is the topmost or outermost layer on a roof, exposed to the weather. Many materials have been used as weather proofing material for roofs. The below list is the low down on many different types of roof materials that can be used to give a weather proof finish:

Asbestos shingles - Very long lifespan, fireproof and low cost but now rarely used because of health concerns

Asphalt shingle - Made of bitumen embedded in an organic or fibreglass mat, usually covered with coloured, man-made ceramic grit. Cheaper than slate or tiles. Various life span expectancies

Built-Up Roof - Multiple plies of asphalt saturated organic felt or coated fibreglass felts. Plies of felt are adhered with hot asphalt, coal tar pitch or adhesive

Ceramic tile - Life expectancy of 20–60 years

Concrete - Usually reinforced with fibres of some sort

Fabric - Not commonly used

Flat-seam - Metal with soldered seams

Galvanised steel - Frequently manufactured with wavy corrugations to resist lateral flexing and fitted with exposed fasteners. Widely used for low cost and durability. Sheds are normally roofed with this material. Known as Gal iron or Corro, it was the most extensively used roofing material of 20th century Australia, now replaced in popularity by steel roofing coated with an alloy of zinc and aluminium, claimed to have up to four times the life of galvanized steel

Hardwood - Very durable roofing found in Colonial Australian architecture, its use now limited to restorations

Imbrex and tegula - Style dating back to ancient Greece and Rome

Mechanically seamed - Metal with concealed fasteners contains sealant in seams for use on very low sloped roofs

Membrane - Membrane roofing is in large sheets, generally fused in some way at the joints to form a continuous surface

Metal roofing - Generally a relatively inexpensive building material

Metal shakes or shingles - Long life. High cost, suitable for roofs of 3/12 pitch or greater. Because of the flexibility of metal, they can be manufactured to lock together, giving durability and reducing assembly time

Modified bitumen - Heat welded, asphalt adhered or installed with adhesive. Asphalt is mixed with polymers such as APP or SBS, then applied to fibreglass and/or polyester mat, seams sealed by locally melting the asphalt with heat, hot mopping of asphalt, or adhesive. Lends itself well to all applications

Polyester - Not commonly used

PTFE - Synthetic fluoropolymer embedded in fibreglass

Red cedar - Life expectancy, up to 30 years. However, young growth redcedar has a short life expectancy. High cost. Should be allowed to breathe

Roof tiles - Used throughout the world, tiles are versatile and are the most common choice for weatherproofing a roof in conjuction with a roof membrane

Seagrass - Used in coastal areas where there are estuaries such as Scotland. Has a longer life than straw. Claimed to have a life in excess of 60 years

Shingles - Called shakes in North America. Shingles is the generic term for a roofing material that is in many overlapping sections, regardless of the nature of the material. The word is also used specifically to denote shingles made of wood

Slate - Life expectancy of up to 150 years. Being a heavy material, the supporting structure must be very robust

Sprayed-in-Place Polyurethane Foam (SPUF) - Foam sprayed in-place on the roof, then coated with a wide variety of coatings, or in some instances, covered with gravel

Standing-seam - Metal with concealed fasteners

Thatch - Roofing made of plant material, in overlapping layers

Thermoplastic (e.g. PVC, TPO, CSPE) - Plastic sheets welded together with hot air creating one continuous sheet membrane. Can be rewelded with the exception of CSPE. Lends itself well to both big box and small roof application because of its hot air weldability

Thermosetting plastic (e.g. EPDM rubber) - Synthetic rubber sheets adhered together with contact adhesive or tape. Primary application is big box store with large open areas and little vertical protrusions

Wheat Straw - Widely used in England, France and other parts of Europe