By Randy Frassetto
Published Tuesday, July 24, 2012
| From the September 2012 Issue of FireRescue
One of the biggest challenges firefighters face involves tailoring their tactics to the ever-changing construction industry. Often, materials used, especially on rooftops, pose specific challenges that ladder companies must be able to adapt to if they want to properly ventilate a fire.
Additionally, it’s important for ladder companies to 1) know when they can and can’t go to the roof, 2) have more than one way to vent a building, 3) have an intimate knowledge of building construction and 4) have a tactical plan for their operation(s). Therefore, in this article, I’ll look at the two main types of tile roofs, discuss how building construction plays a role when they’re applied and explain general techniques for overcoming the challenges that these roof coverings present.
Tile Types & Challenges
There are two main types of roof tiles: clay and concrete. Clay tiles are usually found on older homes and most often have conventional framing below them. They weigh 12–16 lbs./square foot, vary in widths and have an “S” shape to them. Installation uses small cables that run from the ridge to the ledge of the roof, with each tile being attached to the small cable individually.
When clay tiles are nailed down, each tile on every row is attached individually. But as clay tiles age and crack or break, a common practice has been to fill them with concrete to prevent more breakage. Today, the practice of cementing broken tiles has become aesthetically acceptable; it’s common to see concrete protruding from every tile on some roofs because it gives the roofs a “Tuscan” look.
Concrete tiles are newer to the construction world than clay. They weight about 10 lbs./square foot, come in both flat and “S” styles and most often measure exactly 12 inches in width. Many builders, both residential and commercial, install them as their primary rooftop material, with trusses designed for their installation.
Concrete tiles adhere to a “nailing schedule” and often are only nailed in on the first few top and bottom rows. Depending on the pitch of the roof, tiles may also be required to be nailed every row or every other row.
Both clay and concrete tiles, whether applied residentially or commercially, pose challenges to roof crews because:
- Interlocked tiles may often hide roof sag and give a false sense of tenability of the roof when there’s attic involvement.
- Depending on the method used to attach the tiles, it may take additional time to remove them, which will force firefighters to remain on the roof for an extended amount of time.
- Firefighters may not be able to determine whether trusses were designed to carry the weight of tile and, in older applications, rafters may not be able to carry the weight of a ladder company.
Trusses & Tiles
Each building type has its own associated hazards for conventional and lightweight construction; therefore, fire departments must design their tactics in response to each hazard. For example, lightweight, engineered trusses, both residential and commercial, are designed to carry tiles as well as both live and dead loads. Simply put, they’re extremely strong, but they may rapidly fail when impinged by fire. In older, conventionally framed buildings, the structural members of the roof are greater in mass, but they may have been weakened due to age or termites.
To reduce the hazards associated with both conventional and lightweight construction, it should be common practice to pre-plan neighborhoods and/or communities in your first-due area. Houses in many communities are constructed similarly, which may give you an idea of what type of roof you’ll be operating on; however, although reputable roofing companies ensure that roofs are designed to carry the loads of tiles, firefighters should be skeptical of tile roofs that are sitting on trusses that weren’t designed to hold the additional weight.
To Vent or Not?
Today, flashovers are happening within minutes of a fire’s ignition; therefore, a building with smoke and fire inside (e.g., a contents fire) must be ventilated aggressively to reduce the chances of flashover. Positive-pressure attack is one great way to ventilate buildings, but it may not be possible if firefighters have already made entry. Of course, if no ventilation occurs, whether horizontally or vertically, sending crews interior may be asking for problems.
When responding to a fire, the company officer (CO) should be thinking of the location and type of fire that their crew may be facing. There are two main types of fires: contents fires and structure fires. Each has its own set of hazards.
To determine whether a contents fire is occurring, COs should read the smoke and look at open doors, windows, etc. Once identified as a contents fire with no structural involvement, a CO’s priority should be making the interior tenable for crews.
In a working contents fire, interior crews may encounter high heat and low visibility. It’s also more likely that a flashover, not building collapse, will be a major hazard; therefore, vertical ventilation is a good option.
In a structural/attic fire, the potential for building collapse is high. Firefighters may experience good visibility and may not be operating in flashover conditions, but fires in the attic space, especially in lightweight construction, promote rapid structural collapse of trusses that are exposed to direct fire impingement. Firefighters may be operating underneath a fully involved attic space where a truss can fail in as little as five minutes. A full roof collapse is also very possible, so ladder crews should be hesitant to even go to the roof.
A vent hole on an attic fire may be considered a “fire break” and may help slow down the fire’s progression, but a hole should only be made if there’s a large amount of rooftop on which crews can operate to avoid working over trusses that have caught fire.
Structures often have fires that begin in livable space and extend into the structure, or construction components. Buildings that have a significant amount of fire in both the interior and the structure may be in danger of both flashover and building collapse.
When responding to a structure fire, one of your main priorities will be to determine whether you’ll be dealing with a contents fire, a structure/attic fire or a combination of both. If attic vents are present, use them to help determine if there’s attic involvement and what direction the fire is going. Note: Even in a contents fire, light smoke may emit from the attic, but pressurized smoke is a sign of fire in the attic. Also check the front door and windows—smoke coming from these openings or smoke-stained windows may be a sign of a contents fire.
Next, ladder the unburned side of the roof as near as possible to where you’ll create a vent hole. When dealing with concrete tiles, if attic vents aren’t present, or the first crewmember wants to confirm the conditions in the attic space, push up a tile and create a smoke-indicator hole. Note: When laddering the building, pay attention to the overhang, and ensure that the smoke indicator hole is past a load-bearing wall.
In most cases, both flat and “S”-shaped concrete roof tiles are exactly 12 inches wide. With the sawyer remaining on the load-bearing wall, three tiles can be pushed straight up using an axe or trash hook. Since common truss spacing on a roof is 24 inches on center, pushing up three tiles (36 inches wide total) will allow you to find a truss within that space.
Once you push up three tiles, the center rafter can be located by sounding or making a back-cut with a chainsaw.
With the sawyer still remaining on the load-bearing wall, the other two crewmembers can work their way to the ridge of the roof by keeping their inside foot on the center rafter and their outside foot on the outside rafter.
Tip: Concrete roof tiles are laid from right to left, so if the crew is having trouble getting their fingers under the tiles, the crewmember on the right side can lift up one tile with a tool, creating a gap across the row so tiles can be easily removed.
Crewmembers can remove three tiles from their inside foot to their outside foot, which will create a 6' area where the sawyer can make the head cut. Removing 6 feet instead of 4 feet will ensure that the sawyer can make a full 4' head cut, leaving a 1' foot path on each side to operate on, if needed. Tip: As mentioned earlier, tiles are nailed down at the top and bottom three rows only, so they may be easier to remove if you start lifting from the top row.
Once an area of 6 feet across and approximately 6 feet down has been cleared, the sawyer can walk up the center rafter and perform a center rafter louver. Creating a 6' space for cutting allows the sawyer to complete a 4' head cut. This leaves one foot on each side to louver the cut, which means the sounder won’t need to stand on the tiles and ensures that they remain on a structural member. Note: If the hole needs to be extended, continue to remove tiles from the row you originally pulled from in a downward direction.
A Final Note
The ever-changing construction industry challenges firefighters to stay on top of their game. By developing an understanding of building construction, and building construction materials, we can better determine when it’s safe to go to the roof, and develop proper tactics for safely and effectively venting various rooftop materials.
In my next column, I’ll discuss the approach you should take when dealing with clay tiles.
Sidebar: Want More Info?
For more information on UL’s continuing ventilation research, visit http://www.ul.com/global/por/pages/offerings/industries/buildingmaterials/fire/fireservice/ventilation/.
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