There are a range of roofing materials to choose from, but what are the benefits and drawbacks of each, and how long do they last?
Roofs are critical because they not only shield the rest of the building, but they also have to withstand the highest levels of solar radiation of any part of the house, as well as significant wind, rain, and hail. The roof must also be able to accommodate additional structures including solar panels and solar hot water systems, satellite dishes, ventilation and air conditioning systems, as well as the weight of people building and maintaining such systems. It also serves as a rainwater collection system for your home and garden. Corrugated iron and color bond steel, concrete, ceramic, metal, and composite tiles, slate, shingles, and even load-bearing panels like SIPs (structural insulated panels) are only a few of the roofing materials available . Each choice has its own set of benefits and drawbacks, as well as a distinct look and a variety of choices for that specific result.
The roofing you choose will be decided in part by the materials and overall appearance of the entire house, as well as your personal preference, which can be influenced by a variety of factors such as appearance, the material’s eco-credentials, the selection of colors and styles available, the construction method, the amount of roof maintenance you’re willing to provide, the requisite fire resistance, and, of course, the home’s location and therefore surrounding environment, including any heritage or architectural standards imposed by your local council.
i. Galvanized iron/Color bond steel
These products are made from thin steel sheets (typically less than 1 mm thick) that have been coated with zinc, an aluminum/zinc/magnesium alloy (Zincalume), or a paint over zinc alloy (Color bond).
Sheet steel goods are all screwed (or even nailed) to wood or steel battens, or they are clipped onto hidden brackets that are screwed to the battens. Both methods overlap the sheets’ edges to avoid water infiltration, but hidden fixing systems remove the piercing of the sheets caused by screw or nail fastening and provide a more reliable weather seal. Ridges are completed with custom capping, and different styles of gutters usually complete the eaves detailing to give the roof a neat and tidy appearance.
The benefits of sheet steel products are numerous. They are light and relatively easy to handle (though extreme caution should be exercised on windy days), easy to fasten and install (at least for professionals), very sturdy, and can last for decades with minimal maintenance if installed correctly. They are also highly fire resistant, despite the fact that heat and sound will pass through them.
When cleaning gutters, improperly mounted sheeting can become a sharp hazard if the sheets reach too far into the gutter.
These are made up of two sheets of coated or painted metal, such as Color bond sheeting, bonded to either side of an insulating foam layer. They are very strong, lightweight, and simple to mount, and they can provide a home with the first layer of thermal and acoustic insulation. Since these panels come in thicknesses of 125 mm or more, they can provide significant insulation. Maintenance is minimal, similar to that of standard sheeting materials.
All tiles have the benefit of being readily replaceable if they are damaged, such as by falling tree limbs or being stepped on. Unlike sheet materials, you just need to repair the damaged portion of the roof, not the entire roof from cap to gutter. Let’s take a look at some of the more common materials used for tiles these days.
i. Concrete tiles
Concrete tiles are constructed from a mixture of cement, sand, and pigments that is cast or pressed. Traditional types, flat slate-like tiles, bevelled and textured tiles are all available in a variety of colors and patterns.
Concrete tiles are prone to cracking because they lack the internal reinforcement used in structural concrete. They’re easily broken if they’re stepped on after being wrongly installed (a common issue after rooftop operation, such as installing roof-mounted devices), dropped during installation, or hit by falling tree limbs and the like. Concrete tiles can last for up to 50 years or more, and if care is taken when a house is deconstructed, concrete tiles can be reused in another construction project. Crushing old tiles may be used as fill material in new concrete or for other construction projects.
Concrete tiles have the drawback of being heavy, because although concrete has a low embodied energy per kilogram as compared to other roofing materials, the high mass per unit area covered as compared to sheet and related products results in a comparatively high embodied energy for an overall roof.
Furthermore, because of the high mass of the tiles, roofing structures must be capable of supporting the weight of many tons of tiles for the duration of the building’s existence. Since tiles are small, roofing battens must be placed close together, requiring more materials for the roof construction and taking longer to install than sheet items.
These tiles will reduce outside noise through the roof by as much as 30 dB
ii. Clay tiles
Clay tiles are usually manufactured from terracotta clay that has been fired to about 1100 degrees Fahrenheit, resulting in a vitrified tile that is waterproof. They come in a variety of colors and profiles and will last a long time if properly cared for. Clay tiles have a higher embodied energy per total roof area than sheet products.
Since they are made of ceramic, they are fragile and easily break if poorly handled, so caution should be used when handling and installing them. Since broken ceramic tiles are an inert material, they can be crushed and used as filler in new concrete or elsewhere, much like concrete tiles.
Clay tiles have a reasonable sound-deadening impact on outside noise, so they might be better suited to high-noise areas such as near highways and airports. Clay tiles, like concrete tiles, are heavier than sheet roofing materials, needing additional roof support structures, which can increase construction time and costs marginally.
iii. Metal tiles
Metal tiles are made from pressed sheet metal and are constructed to resemble ceramic or concrete tiles. They have the benefits of being lighter than masonry tiles, stronger than sheet materials, and more easily replaced if they are damaged.
Pressed metal tiles are usually painted, such as color bond, or have a textured coating that mimics the appearance of concrete tiles. Both coatings are susceptible to damage from falling debris, foot traffic, and strong hail impacts over time. If anyone steps in the centre of a metal tile instead of the top and bottom edges where the battens are, the tile can be dented to the point of requiring replacement.
Metal tiles have the advantage of being able to replace multiple concrete or ceramic tiles with a single large tile, allowing for quicker installation.
These tiles can be recycled through standard metal recycling channels because they are mostly metal (steel or aluminum).
iv. Slate tiles
Slate gives a roof a pleasant look, but it’s fragile and heavy, so it needs to be installed by a professional roofer with slate installation experience. If you’re thinking about slate, look for a slate supplier/installer with a lot of experience.
Slate has a very long lifespan if installed and cared for correctly.
v. Composite tiles
These are made of reinforced plastic composites, similar to the recycled plastic decking that has become common in recent years, but composite tiles are made of virgin resins (not recycled) for long-term durability. They are much lighter and stronger per unit of area than clay, concrete, or slate tiles, and are UV and hail resistant.
Composite tiles have a low embodied energy as compared to other materials, but since they are made up of plastic and reinforcing fiber, they are less reusable/recyclable.
vi. Asphalt shingles
They are made of thin felt sheets impregnated with asphalt and then coated on both sides with another layer of asphalt. To make the final finish, mineral stabilizers are applied to improve fire resistance and longevity, and the top surface is covered with colored crushed rock.
Asphalt shingles are more of a final finishing material than a structural roofing material, as they are spread over sheets of marine-grade ply that provide roof rigidity and support.
To increase the final roof’s weather resistance, another layer of asphalt-impregnated felt or similar material is normally laid down over the ply before the shingles, making their installation more complicated than other roofing systems.
Asphalt shingles are simple to work with because they are light, thin, and flexible, and roof capping is done with the same shingles folded over ridges, making them ideal for DIY use—though installation can be time-consuming. If assembled according to the manufacturer’s instructions, the product will last for 50 years or more.
vii. Wood shingles and shakes
Timber shingles and shakes are arguably the most environmentally friendly roofing materials because they are entirely renewable and biodegradable, as long as they are sourced responsibly. They’re only bits of wood cut into tile-sized boards with a set height but variable width, typically between 10 mm and 14 mm thick at the butt or up to 25 mm thick for shakes.
They’re simply nailed into place and, if needed, given a coat of wood oil or other preservative, though some may be left untreated. Wood shingles are typically installed on a plywood substrate, which provides the majority of roof strength and a continuous surface to nail through, allowing shingles to differ in size without the use of complicated batten systems. Timber shingles can be made from any suitable timber and even cut on site with the right tools.
Polycarbonate, PVC, and fiberglass are three popular types of transparent or translucent materials that transmit light into an environment. They are commonly used in open spaces like verandahs or garages.
Because of their lower strength compared to steel sheets, load-spreading washers designed specifically for their profile are typically used to prevent screws from pulling through the sheet during strong winds. The most popular form of light-transmitting sheet used for domestic roofing is polycarbonate. They come in a variety of profiles, tint colors, and light/heat transmission ratings that vary from fully transparent to almost opaque. In most cases, polycarbonate roofing can be expected to last at least 15 years, and sometimes much longer.
Cellular sheeting is a type of polycarbonate sheeting that consists of two or more parallel sheets separated by small walls to form several parallel tubes. The thickness of this material varies from 3 mm to 40 mm or more for commercial grades, and it is usually smooth rather than profiled. It’s a popular choice for greenhouses and commercial facades. Insulation is possible with cellular polycarbonate sheeting. The air trapped in the material’s cells forms an insulating blanket similar to double glazing, and some of these panels can provide excellent thermal insulation, reducing heat loss from interiors—one reason they’re used in some commercial greenhouses.
PVC is similar to polycarbonate, but it is less expensive to manufacture and more harmful to the environment. It’s also not approved for prolonged sun exposure, so it’s not widely used.
Fiberglass sheeting, like polycarbonate sheeting, comes in a variety of profiles, colors, and light and heat transmission levels. Glass fiber reinforcement, on the other hand, will make it thicker than other light-transmitting sheeting. The only con is that it has a short lifespan.
The biggest environmental disadvantage of nearly all light-transmitting roofing sheets is their inability to be recycled at the end of its life cycle. Transparent roofing sheets that aren’t tinted emit a lot of the infrared radiant energy that falls on them, so they’re not very good at insulating. Tinted roofing sheets, which are available in a variety of colors and light transmittance levels, can reflect heat more effectively.
So, what roof design should I choose for my project?
There is no clear answer because this is determined by a variety of factors, including the rest of the house’s architecture, the location and orientation of the house, the environment, and the need to accommodate other roof-mounted equipment such as solar panels. The variety of roofing materials available will be influenced by the roof design.
The angle of the roof should be carefully considered. While flat roofs are basic, they do have some drawbacks. For starters, they always lack sufficient room for adequate insulation, though this can be remedied with better design. A flat roof is rarely the best choice in areas where temperatures are high. Flat roofs also necessitate the mounting of solar panels or solar water heaters on tilting frames, which can be unsightly and add to the cost of installation while also significantly increasing wind loading on the roof. Another problem with flat roofs is whether they can shed water quickly enough, particularly in high-rainfall areas. Steeper roofs shed rain more quickly, allowing other debris like accumulated mud, leaves, and other debris to be removed more easily than like a flat roof.
Roof pitch will also affect the total cost of the project, with higher pitched roofs experiencing more wind loading and therefore requiring structural reinforcement, as well as having a wider surface area and thus requiring more roofing materials.
So, although that high-pitched roof can look stylish, think about the cost of construction. Of course, if you design the house so that the steep roof can accommodate a living space rather than adding a traditional second storey, the equation shifts, and the higher pitch can actually lower the construction cost.
Thermal properties; Thermal mass is the ability of a material to absorb and store heat energy. Concrete, clay, and slate tiles store much heat. In the summer, this is a drawback because it creates a hot blanket of material on top of a house that is desperately trying to cool! Roof sheeting materials have a low mass, so they absorb heat quickly but also radiate it quickly, unlike concrete or ceramic tiles.
Composite tiles are expected to outperform concrete or clay tiles in terms of thermal performance while limiting the high thermal mass. Asphalt and wood shingle roofs have a limited but observable amount of insulation ability due to the plywood substrate and the insulating ability of the shingles.
Maintaining temperature in your home
i. Insulation; In order for the house to perform well thermally, the roof design must allow for sufficient insulation to be added.
ii. Ventilation; Another method of heat mitigation for cavity roofs is good ventilation, which can be either passive or forced. Vents are placed on opposite sides of the roof to allow for cross-ventilation from breezes in passive ventilation. The rotary ventilator, which is rotated by the wind and uses either a collection of fan blades or the venturi effect to try to remove hot air from the roof cavity, is a common but ineffective method of forced ventilation. Hot days, are often still days, as the wind speed is inadequate to remove enough hot air from the roof cavity to make a difference.
A suitable sized solar ventilator, which uses a solar panel coupled with a DC fan to remove hot air, is a better choice. Any ventilator must be able to remove the entire volume of the roof cavity every 10 minutes or so and even faster on extremely hot days, so you’ll need a ventilator that’s the right size.
If a home already has a solar panel on the roof, using a mains-powered ventilator is easier and more cost-effective, since it can pull its electricity from the solar panel.
Ventilation is used for more than just temperature control; it also helps to prevent moisture accumulation and the issues that come with it, such as mould growth and rot in structural wood. However, the amount of ventilation needed and when it should be active are determined by the home’s architecture, air tightness, and local climate.
If a home is being re-roofed, an inspection should be performed to see if moisture has become a concern, and proper ventilation should be installed to correct any problems.
iii. Color of your roof; Light-colored roofs will reflect more heat than dark colored roofs.
Color bond sheets have infrared reflective coatings that, while being black, can help minimize roof cavity temperature by reflecting more infrared than normal paint or tiles of a similar hue. Although there is no magical replacement for a lighter-colored roof, such coatings will help to reduce a home’s heat load.
iv. Shading; Shading would also significantly reduce the amount of incoming heat, but shading is not an option if you choose to install solar panels on your roof.
The panels, on the other hand, can provide some heat reduction. Although they will heat up and reradiate some of the heat to the roof from their back surface, the amount of heat reradiated will be significantly less than the amount of heat reradiated from direct radiant sun on that portion of the roof.
Convective airflow between the panels and the roof may occur on a sloping roof with a fair distance between the panels and the roof (at least 50 mm), helping to reduce temperatures for both the panels and the roofing.