Fire: what can prefabricated structures withstand?

There was a fire in a prefabricated family home in Diósd. The building was certified to have been built with good quality and a superb structural system. It was a single-storey wooden-frame prefab house, built on a concrete-structured basement. The wall panels were factory-made: the hollow external wall was filled with stranded heat insulation, its interior had an 18mm thick fire-resistant plasterboard, its exterior a 15mm thick gypsum fiber. During factory production, the external plastering received PS heat insulation. These structural elements were transported to the location and assembled there. The internal division are wooden-frame factory-assembled walls containing noise-insulation, and covered with plasterboard. The ceiling is composed of the roof-structure’s lower beams; 18 mm thick plasterboard covering was installed on location (suspended ceiling).

By the time the fire started, the external and internal walls were all complete. The wooden slab and its 18 mm thick fire-resistant plasterboard covering, and the moisture barrier and heating insulation above it were also complete. The wooden roof-structure and the battens were standing; the structure was foiled. The external doors and windows were installed, the internal wooden door-frames were in place. The internal plasterboard covering on the walls was completely done, the jointing and the ceiling-cover would have been next.

The fire broke out during installation of the water-insulation, in the bathroom, which was temporarily being used to store a large amount of stranded heat insulation material. The large exposure to heat broke the windows; the escaping smoke smutted the façade in a few places.

Level of damage
The fire significantly damaged the interior of the building. In the vicinity of the fire’s supposed source, the plasterboard covering was completely blackened, and the paper layer separated from the impregnated plasterboards in the bathroom. The latter however was due to the water used to put out the fire, and not the fire itself.

The interior wall and ceiling covering was blackened according to the spread of the smoke. This did not cause structural damage, but it was more economical to replace the smut-polluted sheets. Bricks in similar situation also had to be replaced.The installed wiring suffered a great deal of damage due to the heat.

The door-frames near the fire were charred, further ones were simply blackened.

The spool of heat-insulation material stored in the bathroom was destroyed, but its presence protected the wall from further damage. The heat-insulation was exposed to smoke due to the incomplete jointing. The removed wall segments revealed that the insulation’s smut-damage was concentrated around the joints.
The damage affected all of the division walls, the entire ceiling covering, the internal covering of the outer walls, and the insulation.
The escaping smoke blackened the façade’s polystyrene layer and the porch’s covering.

Fire safety
The plasterboard wall and ceiling was exposed to the fire before jointing. Thanks to the plasterboard, the fire did not directly reach the wooden ribs and the wood beams of roof structure. Although the plasterboards’ paper layer started to separate, the bolting held, and the gypsum core withstood the fire without falling apart. . The pictures well illustrate the effectiveness of fire-resistance.

When examining the building from a fire-hazard perspective, we noticed that the insulation and the plasterboards provided a great deal of protection against the fire. Although both materials began to disintegrate, the water used to fight the fire caused the most significant destruction.

Following the fire, the repair work may be limited to replacing the covering and possibly the heat-insulation. No building is designed with the cost of potential fire damage in mind. Yet the low cost of repair is clearly an advantage of prefabricated buildings. Simply replacing building blocks instead of complete renovation.

In prefabricated houses, the wiring is placed in the hollow core of the wall. . In case of malfunction, a fire in the core needs to first burn through the plasterboard first. Damage in the hollow core is easily repaired by replacing the wall unit..

The abovementioned example proves, that careful planning and construction can be useful even during the building process. Moreover, good choice of fire-resistant structures and the details of implementation are both essential for quality work.

(Kész-Gyors-Szerelt HÁZ ABC - 2004. 2.)