ROOFS AND DETAILING


styles of roofs

The roofs of buildings also define regions and the era of construction. Cold climate usually have steeper pitched roofs which will shed the weight of snow more easily. Often, the increase in roof space allowed further stories, resulting in dormer windows.

Roofs in hotter climates have a lower pitch but often have big overhangs to provide shade.

The least satisfactory and attractive roof is a flat one. This is probably why they have been so loved by some of our potty architects!

Below is a guide showing the most common types of roofs.

The weather proofing material is the topmost or outermost layer, exposed to the weather. Many materials have been used as weather proofing material:

  • Thatch is roofing made of plant material, in overlapping layers.

  • Wheat Straw, widely used in England, France and other parts of Europe.

  • 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, Wood shingles longer than 16" are 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.

  • Red cedar. Life expectancy, up to 30 years. However, young growth red cedar has a short life expectancy. High cost. Should be allowed to breathe, usually installed on lath strip for this purpose. The lath may rest on a roof deck with underlay or be fastened directly to the rafters.

  • Hardwood. Very durable roofing found in Colonial Australian architecture, its use now limited to restorations.
    Slate. Higher cost with a life expectancy of 50 to 200 years depending on the thickness and type of slate used. Being a heavy material, the supporting structure must be rated to support the weight load.

  • Ceramic tile. High cost, life of 20-100 years.

  • Imbrex and tegula, style dating back to ancient Greece and Rome.

  • Metal shakes or shingles. Long life. High cost, suitable for roofs of 4/12 pitch or greater. Because of the flexibility of metal, they can be manufactured to lock together, giving durability and reducing assembly time.

  • Mechanically seamed metal. Long life. High cost, suitable for roofs of low pitch such as 0.5/12 to 3/12 pitch.

  • Concrete, usually reinforced with fibres of some sort. Not suitable in climates that experience many freeze/thaw cycles during a year which will cause this type of material to form cracks and fail.

  • Asphalt shingle, made of bitumen embedded in an organic or fibreglass mat, usually covered with coloured red, man-made ceramic grit. Cheaper and lighter than slate or tiles. Life expectancies vary from 20 to 50 years depending on the product. Sun is the enemy of asphalt shingles so longer life can be expected in cloudier locations or at higher latitudes.

  • Asbestos shingles. Life spans vary. Fireproof. Rarely used anymore because of health concerns. Abatement costs can be high when the old roof needs to be replaced and is subject to additional state and local environmental regulation and oversight.

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

  • 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.

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

  • 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.

  • 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.

  • 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.

 
Reed thatch                                                               Wooden shingles

 
terracotta tiles                                                         Imbrex and tegula tiles

 
Bitumen                                                                   Corrugated iron

 
sheet metal                                                          PVC roof