Monthly Archives: December 2016

Green Roof Systems Explained

Extensive or Intensive? Green roof systems come in a variety of shapes and sizes, but they carry multiple benefits. Though they can cost more than a traditional roof, a green roof system can reduce heat loads, reduce stormwater runoff, lower cooling costs, and help reduce the heat island effect in cities.

There are two general types of green roof systems: extensive and intensive.

Intensive green roofs, commonly thought of as “garden roofs,” are the more complex of the two, exhibiting much greater plant diversity, and a greater need for design expertise, experts say. Planting media for intensive green roofs are a foot deep at minimum, and have saturated weights ranging from 80 to 120 pounds per square foot, depending on type and depth of planting medium and the type of plants. Almost always used for new construction, intensive green roofs can be anything from a public garden to an entire park — as is the case with the world’s largest green roof, Millennium Park in Chicago, which is 24.5 acres of landscaping on top of two subterranean parking garages.

Extensive green roofs, with a saturated weight of 12 to 50 pounds per square foot, are the most common. With planting media of 1 to 5 inches thick, most extensive green roofs are not designed for public access or to be walked on any more than a typical membrane roof. Several modular extensive green roof products have emerged in the last few years that allow plants to be grown at the factory prior to actually being installed on a roof.

Even though they are lighter than intensive roofs, extensive roofs shouldn’t be assumed as an automatic fit on every roof. Blanket statements about structures that definitely can or cannot support a green roof are difficult. Many structures actually will be able to support a green roof without any beefing up.

Start with a structural evaluation. You need to know the structural loading capacity because if structural upgrades are required, they’re usually cost-prohibitive.

Green Roof Systems: The Planting Details
Experts’ advise choosing self-sustaining plants whenever possible. Just like landscaping, make sure you’re looking for vegetation appropriate for that locale. You really should be looking for vegetation that doesn’t require irrigation.

There are multiple reasons for this — first and foremost of which is that maintenance is avoided. The less often crews have to go up to the roof to water and pick dead plants, the more time they have for other facility functions. Additionally, a University of Texas study reports that a green roof’s ability to cool interiors and retain water improved when plants native to the area were used. Then there’s the avoided cost of the irrigation water. Finally, some experts in the Southwest and Southern California have suggested that not using native plants, and then not properly maintaining the roof, creates a fire hazard because of the dried-out, easily flammable plants on the roof.

Three Places to Check For Leaks

Roof leaks are a major headache to fix. The good news is that some leaks are predictable – especially as the roof ages. By identifying areas that are prone to developing problems, steps can be taken that will prevent roof problems cost effectively.

Look For Roof Leaks Near Penetrations
Flashings and sealants at penetrations through the roof membrane are common trouble spots. Typically in single-ply roofing systems, penetration flashings are the same material as the roof membrane and are bonded to the field membrane. Inspect the laps, seams and sealants at these locations regularly.

Factory-assembled boots can address field installation issues at penetrations. It is important that technicians properly seal the boot to the field membrane, where problems typically occur.

Roof drains that penetrate a roof membrane can be especially troublesome because rain that falls onto the roof eventually flows over the drain’s seal. Drains should be large enough to handle heavy rainfalls, and they should have a screen that stops debris from flowing down the pipe.

Workers should clean the drain regularly to prevent blockage of the screen and install recessed drain sumps. A positive slope in the roof also can prevent ponding around drains.

The best way to avoid leaks at roof penetrations is to avoid penetrations altogether. For instance, ducts, conduits and other piping that runs horizontally across the roof often are placed on solid supports that are anchored to and penetrate the roof membrane at regular intervals. To avoid these penetrations, managers can specify products with adjustable heights and soft feet that rest on the membrane. If a horizontal element must be anchored to the roof, build a curb and secure the element supports to the curb.

Roof Leaks On The Perimeter

Leaks occur near roof edges because of the transition from flexible membrane flashings to inflexible sheet-metal flashings. Technicians should ensure that sheet-metal laps shed water, and they should inspect the sealants at these locations regularly.

Pre-manufactured sheet-metal roof accessories can solve many roof-perimeter problems. Managers can specify custom-made accessories for copings at parapet walls and reglets at masonry or interior rising walls. These components typically snap together, and technicians can dismantle and re-install them during roof-membrane replacements.

Water problems also occur near expansion joints at roof perimeters. To address areas where building expansions and contractions are likely to occur, managers might want to to consider specifying pre-manufactured roof accessories. But managers need to make sure accessories they specify are compatible with the roof membrane.

Condensation And Roof Leaks

Sometimes, a roof might appear to leak in January when the temperature dips below freezing, but the roof might not be leaking. What happens is condensation is created when the warm, moist interior air inside the building contacts cold surfaces or when cold air leaks through the building’s exterior skin.

This problem might result from a missing or inadequate air barrier or vapor retarder on ceilings or walls, or from inadequate insulation or ventilation. Cold areas above the insulation in joist cavities or attic spaces must be vented. If natural ventilation is difficult or too expensive, technicians can install a fan that moves moist air out of the cold space.

A Guide To Single Ply Roofing Products

Single ply roofing products were born out of the oil crisis of the 1970s, which led to lightweight, flexible roof membranes. Today, a variety of single ply roofing products exist.

Among the common single ply roofing products are PVC, EPDM, TPO and KEE. All these changes mean that selecting single-ply roofing needs to be done with care and forethought. Here is a brief overview of the leading single ply roofing products on the market today.

Single-ply membranes are usually broken down into two subgroups — thermoplastics and synthetic rubber. (Modified bitumen membranes are virtually never installed as single-ply membranes.) Thermoplastics have a common characteristic not found in synthetic rubbers — they can be heated and reshaped or melted multiple times. Because of this, the most common method of seaming a thermoplastic is by heat-welding the membrane. Properly melting the edges together fuses the membrane into a strongly bonded seam.

There are two major thermoplastic membranes currently on the market. These are polyvinyl chloride (PVC) and thermoplastic polyolefin (TPO). A third, KEE, is manufactured by only one company. Although its use is limited, the membrane is notable for being able to pass the test of being hit with a two by four shot from an air cannon.

PVC roof membranes have the longest track record of any thermoplastic membrane, with the first PVC-based systems installed in Europe in the early 1960s. Vinyl membranes are inherently self-extinguishing, which enables them to earn fire ratings from Underwriters Laboratories and Factory Mutual and to perform reliably in real-world flame exposure.

The finished vinyl roof membrane contains polyester or fiberglass reinforcement, vinyl resins, ultra-violet light inhibitors, heat-stabilizers, biocides, pigments and plasticizers. Polyester reinforcement imparts high tearing and breaking strengths needed for mechanically fastened roofing systems. Because PVC is not naturally flexible, plasticizers are added to the formulation. In past years, the loss of the plasticizers in un-reinforced membranes caused catastrophic failures as the membrane reverted to its inflexible state and shattered during cold weather. Now, all PVC membranes are reinforced, and new formulations minimize the loss of plasticizers from the membrane.

TPO membranes have become widely used as roof membranes in the past ten years. A TPO roofing membrane is typically made from polypropylene and ethylene-propylene (EP) rubber polymerized together using state-of-the-art polymer manufacturing technology. This technology enables the production of TPO membranes that are flexible at low temperatures without the use of polymeric or liquid plasticizers.

Unlike some other popular thermoplastic roofing membranes, the TPO polymer does not contain chlorine and no chlorine-containing ingredients are added during sheet production.

The TPO resin is compounded with other components, including a weathering package, fire retardants and pigments, to create a product that can withstand the elements associated with rooftop exposure. TPO itself is not fire resistant and requires the addition of fire retardants to obtain a fire rating. The ratios of weathering material and fire retardants are still inconsistent from manufacturer to manufacturer. Because TPO membranes are inherently flexible, unlike PVC membranes, additional plasticizers are not required in the formulation so there is little danger of plasticizer migration.

Synthetic Rubber: EPDM
Virtually all synthetic rubber roof membranes are EPDM. Synthetic rubber is a thermoset, which means once it has cured, it cannot be melted and reshaped. Consequently, the rubber membrane is seamed by an adhesive — generally either a field-applied contact cement or an adhesive tape that is applied in the field or factory and activated by removing a release paper. Tapes have become the de facto standard as they are generally easier to apply, reducing the chances they will be installed incorrectly.

EPDM membrane rolls can come as wide as 10 feet. Wider rolls require fewer seams. Fewer seams means less chance of seam failure. Because of the roll sizes, EPDM is often used on buildings with very large roofs. EPDM can stretch and relax, so it can easily accommodate thermal expansion and contraction on large expanses of roof.

Like PVC, EPDM roof membranes have been in production for more than 30 years. The systems have gone through several enhancements over time — reinforcing has been added, new seaming and flashing methods and materials have been developed, and white membranes and clean sheets that minimize on-site dust contamination have been introduced — but the basic product is still the same and performs well.

The majority of thermoplastics come in white with other pastel colors available. These white membranes give an initial high reflectance value that can help keep the temperature of the roof and consequently the inside of the building cooler. As the roof becomes older and collects dirt, however, this initial value will decrease unless the roof is periodically washed. Synthetic rubber is available with a white surface, but the more durable membrane is a dark grey color. There are white acrylic coatings for EPDM membranes that can give the same reflectance as the thermoplastics and are advertised as increasing the longevity of the roof by as much as 5 to 10 years.

How To Make Your Roof More Environmentally Friendly

Reduce The Environmental Impact of Your Home’s Roofing System

Many homeowners are interested in reducing their home’s impact on the environment. In addition to basic changes, such as installing energy efficient appliances and low-flow shower heads, it is also possible to reduce a house’s environmental impact by making changes to the roof. Below are some common roofing related ways to make your home environmentally friendly, which can also help lower energy and utility costs.

  • Water barrels:
    A simple and relatively cheap method of lowering a homeowner’s impact on the environment is to place a water barrel at the downspouts of your eavestrough. The water runoff from the roof can be collected and used for outdoor water purposes such as watering the lawn, garden, or cleaning outdoors. Water barrel collection benefits the environment by displacing the water regularly used from a hose and also reduces costs by lowering water usage.
  • Proper insulation and ventilation:
    Proper insulation and ventilation of a roof system can benefit the environment and lower the heating and cooling costs of a home. The reduction in power and fossil fuels used in the heating and cooling processes will help make a more environmentally efficient household.
  • Daylighting:
    Solar reflective tubes are a great way to bring natural daylight into almost any area of a house. Daylighting can provide natural daylight during daytime hours, which will benefit the environment by reducing electricity, and provide healthy natural light to the household. Click here to learn more about daylighting.
  • Trim excess growth around the roof area:
    Keeping vegetation growth from encroaching on a roof area will aid in air circulation and reduce wear and tear on your roof system. Poor air circulation around a roof can create hot spots on a roof system that can cause accelerated aging. Extending the life of the roof system reduces the material usage over time, saves money, and lowers the environmental impact.
  • Roof Maintenance:
    Proper roof maintenance including keeping the gutters, downspouts, and roof area free of debris will help extend the life of a roof system. By utilizing the full life span of a roof system homeowners can delay replacement, which in turn results in cost savings and less material waste.