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ILLEGAL CONSTRUCTION – RAIN ROOFS

Upon arrival, firefighters find a one story CBS home with heavy smoke pushing from vents in the in the eves overhanging the home’s exterior walls. The Battalion Chief in command of the incident suspects a fire that has either originated or extended to the attic. Based on this observation the Chief orders firefighters, protected by a charged hoseline, to pull ceiling immediately upon entering the front door. After forcing the front door, firefighters are surprised to find the house completely clear of smoke but are ready to fight fire over their heads in the attic when they pull the ceiling. When the ceiling is opened firefighters are again surprised and now perplexed to find only light smoke in the attic and no indication of fire. Moments later the Chief reports flames breaking through the roof. What is going on here?

The home in this scenario has had its original roof covered by a second roof; called a rain roof or roof over. When a roof ages and begins to chronically leak, the building owner may find that it is less expensive to construct a second roof over the original one rather than repair it. Building a rain roof also causes less disruption for occupants than performing extensive repairs to the original roof. In Miami-Dade County rain roofs are most commonly constructed to
improve the appearance of a house or to increase the size of a mobile home. In our jurisdiction, it is not uncommon to build a lightweight plywood rain roof supported by 2” x 4” trusses on top of an older, more substantial roof constructed with 2” x 6” rafters and 1” x 4” roof decking boards. The new roof will typically have a greater pitch than the original roof and will impose a significant dead load when it is covered with clay tile. It is hard to believe that photos 1 & 2 are of the same house. Note the decorative stone in photo 2: Its height and pitch at the top are identical to the height and pitch of the original roof.

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Miami-Dade Fire Rescue Training & Safety Division
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Pitched rain roofs are also commonly constructed on mobile homes to improve their appearance, dampen the sound of rain hitting the original flat tin roof, and to increase their size. You can see some amazing, often illegal renovations to mobile homes in this County. For example, the owner of a 1950’s vintage single wide trailer erects 2” x 4” wood trusses spanning 24-feet over the top the top of his trailer, effectively doubling the width of his residence. He covers his new roof with plywood or oriented strand board (OSB) and clay tile or asphalt shingles. The end of the trusses that are not supported by the original trailer roof can be supported by columns to become a car port or bearing walls to become an addition that is as wide as the original trailer (Photos 3 & 4). Photo 3 Photo 4

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The owner may then cover the addition and the trailer’s original metal skin with plywood or OSB, wire lathe and a thick coating of stucco. Sometimes ornamental stonework is added for a nice touch and the result is an attractive home that makes the owner proud of his handiwork and can fool firefighters into thinking that they are fighting a fire in a conventionally constructed residence (Photos 5, 6, 7, and 8).

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Miami-Dade Fire Rescue Training & Safety Division
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These renovations result in a complete structure being built around and over the original trailer. A fire that starts in the trailer will likely go unnoticed for several minutes if it is unoccupied because the surrounding structure will initially contain the smoke and mask indications of fire. The delay in discovering the trailer fire, which is essentially burning inside of another building, will result in an advanced fire upon arrival and difficulty in reaching it.

Rain roofs create a dangerous concealed space that can become a reservoir for fire and flammable fire gasses that can fuel a backdraft, flashover or cause a catastrophic roof collapse. A fire between a rain roof and an original roof cannot be suppressed by conventional attic firefighting tactics, i.e., pulling the ceiling from below and directing streams into the overhead. This would be very difficult to impossible because firefighters would have to penetrate the original roof. Firefighters will have no choice but to direct streams through vents or through holes cut in the rain roof or a gable end (Photo 9).

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A piercing nozzle and a Bresnan distributor are excellent devices to get water into the space between two roofs.

Be Careful Out There!
Miami-Dade Fire Rescue Training & Safety Division
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It is critical to remember that most rain roofs are extremely lightweight and are very likely to collapse after just a few minutes of fire attacking their supports. Collapse of a rain roof can be hastened by adding an additional dead load of roof tiles and imposing a live load of firefighters, who can fall into the fire burning between the two roofs. Firefighters operating on a rain roof will be much safer if they are supported by an aerial ladder. In the absence of an aerial ladder due to apparatus access or order of arrival, it is imperative that crews operate from the safety of a roof ladder to distribute the additional load. Fire officers who send personnel on or under a rain roof have to wonder if the building department ordered engineering calculations to ensure that the structure and its original roof can bear the additional dead load imposed by the rain roof. Further; was the building department even aware that the rain roof was constructed?

A fire involving a rain roof is a perfect example of why it is absolutely essential that companies operating inside a fire building report conditions to the Incident Commander (I/C), who is observing conditions from a vantage point outside the fire building. When conditions reported from inside a fire building are not consistent with what the I/C observes outside it should raise an immediate red flag; something isn’t right! For example, say companies operating inside report that they have knocked down the fire and checked the attic for fire extension but the I/C
observes smoke continuing to push from the roof. Could it be that the companies operating inside are unaware that there is fire over their heads in a space between the original roof and a rain roof? If an I/C cannot adequately observe conditions then it is essential that they designate another officer early on in the incident, to be their “eyes and ears”; observing conditions outside the fire building and reporting them to the I/C and companies operating inside.

Thanks to Chief Tony Garcia (Batt 12C) for his assistance in writing this Safety Zone.

Calendar

Sep 29-30, 2011 Intelligent Firefighting “Be Aggressive . ..Don’t Be Stupid”

With Capt Bill Gustin, Miami Dade Fire Rescue Double Tree Milwaukee City Center Milwaukee, Wisconsin

Sep 29-30, 2011 Intelligent Firefighting “Be Aggressive . ..Don’t Be Stupid”

With Capt Bill Gustin, Miami Dade Fire Rescue Double Tree Milwaukee City Center Milwaukee, Wisconsin

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