Temperatures in cities like Phoenix, Arizona are significantly higher than those in surrounding rural areas. This phenomenon is called urban heat island effect. A city that is warmer than its neighboring rural areas is called an urban heat island (UHI).

The UHI effect experienced due to Arizona Phoenix weather is felt more at night than during the day and during winter and summer. On average the temperature difference between urban and rural areas during the afternoon is around 7 degrees Fahrenheit. In certain areas the difference could reach up to 10 degrees Fahrenheit.

The primary cause of this peculiar condition is human activities, particularly the modifications of land surfaces in cities.

Causes of UHI Effect

Studies identified at least three important factors that contribute to the UHI effect. These are:

1. Reduced area of vegetation in urban cities compared to rural areas. Fifty six percent of UHI effect is attributed to this factor.
2. Dark paving or land surface, which accounts for a six percent difference in temperatures.
3. Dark roofing used on buildings, which accounts for a significant thirty eight percent of UHI effect.

Solutions for UHI Effects

1. A logical solution under the first scenario is to increase vegetation in cities to reduce temperature. However, this method is considered a long-term solution because it will take years, even decades, to enjoy the full benefits of planting trees and improving vegetation in a rural land. Notably, the solution will always be in a catch-up mode because human progress and expansion always lead to fewer vegetation.
2. The second problem could be remedied by installing lighter-colored pavements on city streets. The technology to implement this solution already exists today. Unfortunately, it will require substantial capital expenditures and the resulting improvement in temperature is negligible. This method is not cost-effective and also considered a long-term solution.
3. The third cause of UHI effect has the best solution relative to the other two. Installing reflective and cool roofing on buildings offers the biggest benefit in terms of money spent and period of effectiveness. Compared to the other two solutions, using cool roofs to offset warming is easy to accomplish, relatively inexpensive, and its benefits can be immediately attained.

Cool Roofs to the Rescue

Cool roofs use reflective surface to direct the heat of sunlight away from the structure. A light-colored and reflective surface absorbs less heat from the sun unlike a dark, non-reflective roof. Because of the enormous benefits derived from using cool roofs such as reduction of heat in the building and savings on energy bills, more homeowners are using this type of roofing over conventional roofs.

One of the things to consider when constructing a patio is the roof. A patio roof makes a big difference in comfort, especially during summer months. In selecting a Phoenix roofing style for your patio, choose one that complements the overall look of your house so that your patio appears like a natural extension of your house. At the same time, the roof design should provide you with maximum protection from natural elements.

There are several patio roof designs that you can choose from, the most popular these days being the dome and gable styles. Patio roofs could be constructed using various materials. Each of the different roof designs and materials provide distinct advantages.

Gable. One of the most popular choices for patio roof, gable consists of two angled roofs that meet at the apex in the middle. The pitched roof allows the rain to slide down to the gutter to prevent water pooling while affording maximum coverage from the heat and rain.

Lattice. This type of patio roof consists of lattice-like covering than is thinner and shaped simpler than those used for a pergola and forms a rectangular structure. It is perfect if your home is more contemporary in design. As in other outdoor roofs, using a durable wood that could withstand the elements is the key to long years of service. You can spice it up by adding fabric to the lattice structure, which offers more shades against the sun’s heat.

Cloth. A very practical way of dressing up your patio using inexpensive clothing materials. You only need to put up the posts, attach the fabric using wires to hold it in place, and you have a beautiful shade over your patio to keep the heat away.

Pergola. This is the more traditional type of patio roof, which consists of pergola columns, purlins and rafters. The combination of posts and crossbeams create an open roof. A metal framework acting as roof works just as well to form a more modern pergola. This type of patio can be attached to the side of the house to form a semi-covered patio. A pergola does not always require a flat roof; it only needs an open roof that allows the light in.

Dome. This Phoenix roofing design is gaining popularity among homeowners. While it has a lesser arch than a gable roof, it provides excellent protection against the rain. To make the domed roof of your patio complement the style of your house, you can adjust the height of the dome so that it blends perfectly with your house.

Phoenix has a scorching desert climate with long, hot summers and short, mild winters. Among all cities in the US, it has the hottest average temperatures in summer. If you live in the city, the reflectivity in your Phoenix roofing should be kept in mind. A cool roof with reflective qualities goes a long way towards cooling your house and lowering those energy bills.

Summer is when people think about the condition of their roofs. Dark non-reflective roofs could reach up to 180°F on a windless and sunny day. That is why contractors and managers are turning to white reflective coatings to minimize the effect of heat on roof surfaces and cooling cost of the structure. A good reflective coating could generate up to 30% heat reduction on roofs.

Reflectivity Rates Vary

The best coatings are usually white and smooth, which could be applied on most roofing materials. A newly-applied coating could provide up to 80% reflectivity, meaning that only 20% of the sun’s heat is absorbed by the roof. However, the passage of time and accumulation of dirt could reduce the effectiveness of the roof to up to 50%.

Each roof coating provides a different level of reflectivity. Elastomeric and ceramic coatings can reflect up to 80% of solar heat. White asphalt shingles generally reflect only around 25% of the sun’s heat. The reason is that they have a rough texture, gray in color and a black substrate. Premium white asphalt shingles that use a whiter granule provide more reflectivity of up to 35%.

Composition of Reflective Coatings

White roof coatings contain polymer material such as acrylic and white pigment that make them opaque and reflective. The white pigment could be titanium dioxide or zinc oxide. Up to 70% to 80% of sunlight are reflected back using these coatings. Around 5% of sunlight, corresponding to ultraviolet light, are absorbed by the white coating, thus protecting the polymer component of the coating and the roof from UV damage.

Acrylic is the most common reflective coating in the market. Others types of roof paints that exhibit reflective properties are fluoropolymer, polyutherane, silicone, epoxy and soy-based products. Contractors prefer acrylics because they are water resistant and durable against extreme weather conditions.

Elastomeric coatings use polymer resins made up of silicon and oxygen. They also offer strong resistance against heat, ultraviolet radiation and water.

Maintaining roof reflectivity is important. Factors that could negatively affect high reflectance include a totally horizontal roof and water ponding. The roof could easily get soiled and experience a corresponding loss of reflectance.

During house construction, builders typically have two choices on the types of roofing to put on top of the structure—a flat roof or a pitched roof. Of course, key factors to consider when choosing the type of roof include the design of the house or building, applicability of national and local laws, the owner’s budget and location.

For those interested to know what type of roofing Phoenix demands for its houses and buildings, particularly the use of flat roofs as a practical roofing design in the area, we compiled a list of the advantages and disadvantages of flat roofs. Based on the pros and cons listed below and considering that Phoenix has an arid weather and experiences mostly sunny days, flat roof is a viable option.

Advantages

1. Affordable. Cheaper than pitch roof since they use fewer materials and labor. There is also no need for decorative materials, which rack up the cost of roofing.
2. Accessible. Easy to climb on and inspect for regular maintenance because of its very minimal slope and mostly flat area. Applying new coating is easier and cheaper too.
3. Wind Resistant. The flat nature of the roof offers the least wind resistance compared to a pitched roof. This feature is vital during storms when strong winds could rip off tiles and shingles attached to pitched roofs.
4. Extra Space. You can use the roof as an extra space to store materials and supplies. You can even design a green roof or garden on a flat roof.
5. Design Adaptability. Great for small structures such as garages, porches and extensions. They are also the best roof type for buildings and other large structures.
6. Facility of Repairs. Expert roofers can complete full replacement of roof coatings in a single day.
7. Durable. The materials used on flat roofs can withstand ordinary wear and tear and last for up to three decades.

Disadvantages

1. Maintenance Needed. It requires regular checkup and maintenance (recoating) to ensure the roof remains leak-free.
2. Potentially Expensive. A flat roof’s coating may require an earlier replacement than pitched fork if not properly maintained, which makes it more expensive than angled roof.
3. Not Snow-Proof. They are unable to withstand the weight of snow accumulation during winter season and heavy rain during storms.
4. Aesthetics. Some people regard certain coating materials used on flat roofs such as synthetic rubber as physically unappealing. Sometimes flat roofs do not harmonize with the general designs of the house in the vicinity.
5. Instability. The larger the area covered by the flat roof, the less stable it becomes.

One of the hottest cities in the US is Phoenix, Arizona. It holds the highest average temperature during summer among major cities with temperatures exceeding 100 degrees.

Because of the hot Arizona Phoenix weather, keeping cool is a primary consideration in house construction and repairs. Most structures use air-conditioning to keep the temperature cool inside. However, this is not the primary factor planners have in mind when constructing houses. Their priority is the roof, particularly using the correct materials and design to combat heat.

Builders choose from a wide selection of roofing materials. There are, however, certain materials that are better suited for places with hot weather like Phoenix, Arizona. Some of these are:

Terra Cotta and Clay

The cooling effects brought by terra cotta roofs are found not only on the materials used but also on the design itself. The curved or “S”-shaped roofing materials are placed in interlocking fashion to form beautiful arches. The spaces between the tiles allow air to freely flow and circulate, thereby rapidly dissipating heat and keeping the structure cool inside.

Rubber Membrane

A product of modern technology, rubber roofing is made from thermoplastic or ethylene propylene diene Monomer (EPDM), a synthetic rubber. The reflective properties of the rubber minimize heat absorption from the sun and keep the structure cool. Roofers get extra benefits from using rubber-membrane roofing – waterproofing the roof because of their seamless nature, which further prolongs the roof lifespan by preventing water from seeping in.

Concrete

An affordable alternative to other roofing materials that many builders in hot countries prefer because it takes a long time to heat up from being exposed to the sun. Concretes are either poured to form slab roofs or installed as tiles. An added advantage from using concrete roofing materials is their fire-proof qualities. Roofers can enhance the cooling capabilities of concrete roofs by using light colors that reflect sunlight.

Slate Tiles

A very common roofing materials that originated during the 17^th century. Slates come from natural stones and are available in light and earth-toned colors. The material’s reflective properties reduce heat absorption from the sun and keep the building interior cooler. Its global use can be attributed to its reputation as a cool material for roofing and availability in places where slates are abundant.

Solar Panels

Phoenix, Arizona with its arid weather and long sunny days is perfect for this type of roofing system. Solar panels or photovoltaic roof shingles do not actually reflect sunlight but absorb them and convert the heat into electricity.