Roofing materials are products used to cover and protect the top of a structure or building. The materials are specially chosen to defend against exterior elements such as rain, snow, direct sunlight and extreme temperatures. A mixture of several materials creates the outermost layer of a roof.

Roofs and primary roofing materials like woven lattices of sticks and straw or mud date back to the prehistoric era. From the time construction of shelters began, it was apparent a protective layer needed to exist. Mud, wood, stone, and metal roofs have been around for thousands of years. Evidence of these materials is found all over the world. Examples of rudimentary to advanced roofing structures have been discovered in ancient Mayan temples, early palaces and religious structures in European cathedrals.

In the past, the prominent materials used in the vast majority of roofs were made of uncomplicated and natural materials such as thatched straw, sticks, mud or wood. The use of these supplies continued up until the Industrial Revolution. In the last century, mass manufacturing has made affordable roofing materials ubiquitous in all applications around the globe.

Materials

The raw materials used in roofing materials are nearly as diverse as their types. These items include:

• Straw and plant-based materials

• Bamboo

• Wood

• Asphalt

• Concrete

• Clay and other ceramics

• Rocks and formed Stone

• Metals, such as steel, aluminum, copper, tin and metal alloys

• Thermoplastics

• Glass

• Fiberglass

• Organic fiber

• Rubber

• A vast array of synthetic materials used in membranes

Types

Roofing materials are extremely diverse with countless color, texture and variations of base ingredients. For example, wooden shakes comprise of several varieties of hard and soft woods while asphalt shingles mix additives such as rocks, sand, glass, rubber and plastics.

The standard makeup of roofing materials include:

• Sheet metal and tin

• Specialized metal coverings such as steel, copper, steel coated with a zinc or aluminum alloy and stone-coated metal

• Thatch made of overlapping plant stalks or sea grass. Predominantly used in developing or undeveloped countries

• Slate made of natural types of stone

• Stone slab constructed from heavier pieces of stone. Now obsolete except in certain restorations

• Shakes, made of split pieces of wood, typically red cedar

• Shingles, which are flat rectangular coverings cut on all four sides in a select size. Made from asphalt, with less traditional options available in wood or other materials

• Tiles that curve or remain flat. Produced from clay, ceramic materials, stone, plastics and wood

• Hot mopped asphalt or tar roofing, applied to partially flat or mainly flat roofs

• Liquid roofing for liquefied rubber. Self-adhering, seamless and immediately waterproof—hardens into a solid after application

• Paneled roofing made of metal, glass, plastic or similar materials

• Polycarbonate sheeting

• Concrete or fiber cement reinforced with a type of fiber

• Engineered solutions consisting of bituminous membranes, thermoplastics, mastic asphalt, fabric, polyester or related materials

• Solar photovoltaic panels. These panels do not provide weatherproofing. However, they generate electricity

• Green roofs comprised of soil, gravel, mulch and vegetation

Individual roofing components and groups of components are fitted to overlap one another. The overlapping of pieces and the natural effects of gravity create a natural downward flow of water and other debris. Flat roofs incorporating a similar arrangement use variations of overlapping to account for the lack of downward angles in their design.

Shingles or fastenings with metal roofs combine with underlayments of tar paper or similar synthetic layering options. The layer is placed on top of the primary roof structure, such as wood, hard plastic or fiberglass. The combination creates a partial seal between the porous and non-porous materials, preventing moisture from finding its way into the central structure. The shingles complete the protective layer.

Features

Roofing materials offer varying levels of effective weatherproofing for specific lengths of time. Additionally, the vast diversity of options assists in accommodating specialized functions for an array of intended uses. The climate is a primary factor. Materials must meet the requirements for unique weather and extreme conditions of the area. An example of popular choices for extreme climates is green roofs and thermoplastics. These offer higher levels of insulation, keeping cold air in and hot air out during high temperatures.

The life expectancy of a roof is directly tied to the materials used in fabricating the main product. The average roof lasts from 10 to 20 years when constructed with materials such as wood, rubber, tar and asphalt. The use of stone and slate provides up to 100 years of protection. Copper roofs span many 100s of years and have been known to last more than 1,000 years.

The esthetic impact of a structure is closely related to its roof design. It can compliment the architecture or serve little to no purpose in design congruence. This detail is of particular importance for residential homes, where curb-appeal is as important as functionality. There is an enormous selection of materials expressly designed for a distinctive look while still serving critical functions. Shingles, shakes and slates are a favorite among homeowners and come in numerous colors, shapes, sizes and textures.

The sun is just one of the harsh outside elements exposed to a roof. As a natural energy source, the consistency of sunlight is a top consideration for alternative energy production. Homes are often built with direct or indirect positioning in relation to the location of direct sunlight. Solar shingles and solar photovoltaic panels take advantage of these principles and are excellent options made to generate electricity.

Applications

Weatherproof coverings are the primary function of materials used in roofing. There are three areas these products are manufactured for:

• Commercial applications

• Industrial applications

• Residential applications

Selecting Roofing

Native climate, cost, endurance and esthetics are the most significant factors to consider when selecting roofing materials. In addition, structural integrity must meet the estimated weight impact of fully installed roofs. Weight is especially critical where heavier products such as stone, slate and concrete are used. The geographical location of a structure may limit its capacity for more dense materials, such as houses or buildings constructed on cliff edges or beaches where and increased pace of erosion takes place.

Residential roofing materials such as wood shakes, shingles and asphalt shingles are the most popular and cost effective. However, these materials do not last as long as tiles or stone slate. Extreme climates require additional insulating qualities, and the ability to absorb or reflect light is a major factor to reaching peak energy efficiency. In many states, high sunlight availability and government incentives make it more economical to install solar shingles or solar photovoltaic panels.

Standards and Publications

AFM 88-3 C8 - Metal roofing and siding

ASTM C1225 - Standard specification for fiber-cement roofing shingles, shakes, and slates

ASTM C222 - Standard specification for asbestos-cement roofing shingles

ASTM C406/C406M - Standard specification for roofing slate

Designing roofs for climate change: modifications to good practice

Image Credits:

J&J Roofing Co. | Triton Systems