Thu, 14 Nov 2013|
Paul Dansbach inspects a house under renovation in which new floors have been constructed of lightweight materials.
[MUSIC] Welcome to Fire Engineering's Training Minutes. My name is Paul Dansbach. Today we're looking at a building on the renovation. The original building was a one and a half story platform framed, wood frame single family dwelling, The type of construction or the construction vernacular for this type of building was refered to as a cape cod style dwelling. Construction terminologians and styles are somewhat regional and will vary from different parts of the country. In the Northeast the cape cod style home is rather popular. The renovation of this building has taken the original platform framed building at one and a half stories. To a two and a half story building that uses lightweight I-joists for the floor systems. The second floor and the third floor floor systems are both constructed with I-joists. We're gonna go inside and take a look at the renovation to identify the structural components and to talk more about the fire characteristics. Of lightweight eye joists floors. We're in the first floor of the house in the renovation. As we look up we'll notice that the original second floor floor joist have been removed and replaced with eye beams, or eye joists. The eye joists bear on the back wall of the house. The c wall of the house. The bearing surface for the eye joist is the top two by four plate. As we move towards the front of the house, toward the a wall, we notice that halfway through the house there is a laminated beam. The eye joists are attached to the laminated beam through the use of a joist hanger. The joist hangers is a dissimilar material, it's steel. The joist hangers are going to be quickly damaged by a fire. The connection point at the laminated beam is not as secure a connection at the C wall where the joist, the bottom of the joist bares on the two by four wall. We're up on the second floor of the house. As we noticed, the third floor floor joists are also I joists. The I joists span from the A wall to the C wall. With a bearing wall about halfway between the A wall and the C wall. One of the ways firefighters can tell what walls, interior walls, are bearing walls. Versus nonbearing walls is the direction of the floor joists. As we notice, our I-joists cross over the bearing wall at a 90 degree angle to the wall. We'll show you a nonbearing wall. A nonbearing wall runs parallel to the I-joist or floor joist. If we follow our floor joist back to the A side of the building, we notice that our I joist there, on a two by four top plate. Directly below the two by four top plate, is a header for a window opening. The header delivers the load imposed upon the two by four top plate. It takes that load. Horizontally transmits the load to the two by four stud wall, which carries the load down through the structure. So far, we've looked at the second floor and the third floor of the building. Both floors are constructed with I joists. Next we're gonna look up under the third floor at the roof system. The roof rafters are constructed with dimensional lumber. It looks like the roof rafters are constructed with 2x10's. There is a tremendous difference in the way the I-joist versus true dimensional lumber performs under fire conditions. We're gonna talk about that in a little bit. We're outside. We're at the sea wall. As we talked about before, the I-joist for the second floor bear on the sea-wall. The I-joist are cantilevered about two feet or so beyond the sea-bearing wall. There is another potential for fire extinction with this construction feature. The fire vents out this window. It exposes the underside of the soffit material. If the soffit material does not offer a fire barrier fire will extend beyond the soffit material and into the combustible void space created by the eye joints. Fire that has access in that combustible void space. Running for the C wall all the way to the A wall in the structure. What we've talked about in this session of training minutes is a house under renovation. We looked at the floor systems. The original floor system of this structure. With dimensional lumber. It was a two by ten. The floor systems that have been added to the second and third floor are I-joists. It's an engineered structural element, sometimes referred to as a lightweight I-joists, or lightweight construction. What it really comes down to. Is mass. Fire resistantness and collapse resistantness of any wood frame building is a function of mass. How much is there to burn before the structural component reaches its yield point and fails? As we see, with the dimensional lumber, there's a significant amount of mass. With out I-joist, the I-joist lack mass. The web of the eye joie will quickly be attacked by fire. It will lead to a quick collapse before summer. Thank you for watching this section of fire engineering's training minutes