Lack of fire separation in the attic of old wooden multifamily buildings is an important cause of the rapid spread of a fire from a fire origin room to the whole building, and it is an important factor in recent collective fires in densely built-up wooden areas.
To protect the flame penetration from the gap in the connecting part of a roof truss, which is sometimes irregular and complicated, and the retrofit attic party wall is necessary to prevent fire progression. In addition, it is expected that the construction work within narrow attic space is full of difficulty. Therefore, it is unrealistic that to apply the wall structure needing the exact construction work such as public notifications to retrofit attic party wall.
In consideration of need processing work including the dimensions adjustment in the attic space inside, the wall structure adopted Gypsum boards in this study.
The development was carried out based on following two points.
(1) A covering material does not penetrate a flame during heating, and do not produce cracks. Because the attic party wall cannot cover with one piece of product, it needs simple and dividable structure so as not to burn from joints.
(2) The gap in the connecting part of a roof truss and the attic party wall needs to be blocked up with simple technique.
Three series of fire tests were performed on in this study.
Experiment1: When a flame invades the attic space of the old wooden multifamily or accommodation buildings at the time of city fire, the flame will be already to be the phase of fire peak. This test carried out an experiment by using the roof-shaped test rig which imitated a roof truss partially, and the burner to reproduce the flame which invade the attic space.
Experiment2, 3: ISO834 wall furnace tests with small-scale specimens and with full scale party-wall specimen.
From these tests, the following conclusions can be drawn.
(1) About the wall of the retrofit attic party wall
・Composed of single layer of reinforced gypsum board (12.5mm) on either side of the stud above the separation wall is desirable. The base materials such as bunches are wood (cedar) of 30×40(mm), and it is necessary to install it every 455mm, and attach the Gypsum boards to it every about 200mm.
・There are no need of filling the insulation material to the hollow layer, and no need of the joint plate.
(2) About the covering method by RWF of the gap in the connecting part of roof truss and the attic party wall
・It needs covering the gap by double RWF both sides (Rock Wool Felt: 10mm thickness, 100mm in width, density 0.2 g/cm3).
・It is desirable to use a screw with the retentivity such as sheet metal screws around 200mm to install the RWF to the roof surface.
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