By Mark van der Feyst
Previously, I have looked at ventilation in relation to truck company operations. In past discussions, I noted that—sometimes—going to the roof to conduct vertical ventilation is not an option. One reason for this is because the amount or size of rooftop obstructions that prevent us from doing so. In the past, we have seen rooftop obstructions mostly on commercial-, industrial-, and mercantile-type buildings. As society becomes more environmentally involved, we are now seeing similar and new obstructions on the rooftops of residential homes.
Obstructions on the roof will prevent firefighters from conducting vertical ventilation because of the weight that is bearing on the roof support members. As the fire develops and grows, it weakens the support members, leading to roof collapse. Incident commanders and frontline officers reading the conditions will recognize the signs of collapse and must prohibit any roof work.
Heating, ventilation, and air-conditioning (HVAC) systems and water tanks are common rooftop obstructions found on commercial, industrial, and business buildings. These common obstructions are factored into the construction of the building for structural stability. However, when fire is present, the structural members will weaken, and roof collapse will be accelerated because of the added weight of HVAC units and water tanks.
As the environmental movement grows, we now see solar panels and rooftop gardens being installed as a way to “go green” with energy production, reducing the carbon footprint. Seeing these obstructions on the rooftops of industrial, commercial, and business buildings is not that surprising, but seeing them on residential roofs is. Government programs paying customers for energy production into the hydro grid entice many homeowners to install solar panel systems on their roofs. Another variation of the solar panel is the solar thermal panel, which is used to heat water with the sun’s heat. Homeowners will install these types of systems to heat their pool water and commercial buildings will use them for areas such as aquatic centers.
Depending on the size of the roof and how much energy a homeowner wants to produce, a solar grid system can vary in size. In photo 1, the house pictured has two sides of the roof covered with 21 solar panels, and there are plans to cover the other two sides with 21 more. The number of sides covered will be dictated by the path of the sun’s travel across the house and the available space.
(1) Photos by author.
Photo 2 shows a nursing home roof covered in solar panels. The amount of space available for vertical ventilation has been removed with the number of solar panels installed for the nursing home and the residential house.
The dangers to firefighters who need to ventilate is two-fold: the added weight of the panels and a live energy source. With residential structures using lightweight truss construction, adding solar panels to the roof adds to the amount of the dead load on the roof. Accounting for added weight in this fashion is probably not in the specs for lightweight roof construction. Typically, solar panels will weigh around 50 pounds each (not including the weight of the hardware and installation systems used). Factor in the weight of the water travelling through—and if a thermal panel system is being used—the added weight applied to the roof increases. The time frame for a lightweight truss to fail is between five and 15 minutes, depending on a few factors. With a solar panel system on the roof of a residential structure, the time to failure will increase. We may have to exercise other methods of ventilation in lieu of vertical ventilation.
The live energy source is the second hazard that firefighters will face. A solar grid tie system used for power generation works with each panel strung together to produce the maximum amount of power. Each panel will produce about 24 to 48 volts (V) each; when tied together, they can produce a range of 120V to 400V. If a firefighter were to cut a vent hole through the solar panel with an ax or a chain saw, the firefighter will feel the full voltage being produced within that grid system. If vertical ventilation is required, the best option is to locate to a spot where the roof can be cut.
Rooftop gardens are popular in many inner-city dwellings and apartment buildings. These gardens come in a variety of layouts, and the inclusion of what to grow is limitless. You will find these gardens mostly on flat roofs, but they can be installed on sloped roofs as well. Switzerland passed a new law requiring all new buildings built to replace the “green” space taken by the building with a green space of equal size on the roof. It does not matter what type of roof is present; the green space must be relocated up to it. This law also covers existing buildings and with different types of roofs. In addition, a school in France is covered by a tent structure that protects a layer of grass on its roof. It performs “double duty” by providing a green footprint while holding the tent in place.
Adding sod, water, and plants to grow food will add considerable weight to the overall roof structure. Even though most installation manuals warn homeowners to seek a structural engineer to gauge if their roof will be able to handle the added weight, adding fire to the scenario will most certainly lead to a quicker collapse of the roof.
When sizing up a residential or commercial building from the exterior, look to see what rooftop obstructions are present and, if found, reconsider what rooftop operations you will conduct in addition to your interior operations.
Mark van der Feyst has been in the fire service since 1999 and is a full-time firefighter in Ontario, Canada. He is an international instructor teaching in Canada, the United States, and India, and at FDIC. He is a local level suppression instructor for the Pennsylvania State Fire Academy and an instructor for the Justice Institute of British Columbia. He is also the lead author of Residential Fire Rescue (Pennwell).
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