- Research
- 22/10/2024
Prof Talk | How fire-safe is sustainable construction?
Innovative construction methods increase fire risks: what does it mean for safety?
Sustainable construction contributes to the energy transition and to energy efficiency, but it also creates new challenges, especially in the area of fire safety. How dangerous are solar panels and how can we take better measures to prevent future house fires like the recent one in Arnhem? Cursor talked to TU/e fire researcher Ruud van Herpen about this.
“In sustainable construction, it’s essential that we adequately ensure fire safety,” says Van Herpen, who, in addition to his position as part-time professor at TU/e, teaches at the fire academy in Arnhem and works for engineering firm Peutz, where he’s involved in several projects as a consultant. He sees the combination of research, education, and practice as challenging and valuable: “Practical projects keep you updated on the latest developments, and at the same time graduation projects can contribute to concrete solutions. The interplay is nice and dynamic.”
Hazards and effects
“When we talk about fire risks, we distinguish between hazards and effects,” Van Herpen explains. Hazards have to do with introducing new ignition sources that increase the risk of fire. When homes are made more sustainable, electrical systems such as solar panels, home batteries, heat pumps and charging stations increase the chance of a fire occurring. Installation errors, poor maintenance, or overloading can lead to short circuits and fires.
Effects relate to how the increased sustainability of homes affects fire and smoke distribution. Oftentimes, fire and smoke spread more quickly due to the use of biobased materials in a well-insulated and airtight building envelope. For example, many biobased materials (such as wood, cellulose, flax, and bamboo) used in sustainable homes can catch fire faster than traditional materials such as brick or rock wool. This may cause the fire to spread more rapidly.
Van Herpen emphasizes that the problem is twofold: not only is the risk of fire higher in sustainable homes, but the use of combustible materials can also significantly increase the effect of fires compared to traditional construction.
House fire in Arnhem
There’s still very little in the way of concrete figures and statistics on fires in sustainable homes, but some well-researched case studies are being analyzed by safety experts. One example is a large house fire in Arnhem in 2023, which destroyed eight ground-level homes. The fire department had great difficulty fighting the fire because the solar panels on the roof blocked the extinguishing water. This allowed the fire to spread through the combustible insulation and air cavities under the roof and in the facade to adjacent homes.
In traditional construction, this would not have happened, as non-combustible materials such as brick and ceramic or concrete roof tiles are used there
“These were traditionally built single-family homes that were sustainably renovated,” Van Herpen says. The renovation involved installing a new roof with solar panels over the existing roof and a new facade in front of the existing facade. The new facade consisted of EPS insulation board, finished on the outside with a thin layer of stucco and thin stone strips. The blaze from a window opening during a house fire ignited the insulation behind the stone strips, causing the fire to travel through the facade to the roof and adjacent homes. As a result, a large portion of the block of single-family homes burned to the ground.
“In traditional construction, this would not have happened, as non-combustible materials such as brick and ceramic or concrete roof tiles are used there,” Van Herpen says. “This means any combustible insulation layer is protected by a non-combustible finish that can absorb a lot of heat. In the case in question, the exterior finish immediately transmitted the heat from the blazing flame to the combustible insulation layer. The combustible facade and the combustible roof caused a short circuit across the fire-resistant partitions, the dividing walls between houses. As a result, the entire block was lost.”
Regulations
The fire raised questions about current regulations and safety standards for sustainable construction projects. “The way the homes in Arnhem were made more sustainable is a popular approach that has been applied to about 70,000 homes in the Netherlands,” says Van Herpen. So was no one aware of the risks? “Of course they were,” he responds immediately. “I have been warning about this for some time now.”
Still, the building complied with the regulations. “The facade met the appropriate fire class, a measure of the facade's fire behavior,” Van Herpen explains. “In this case, it was fire class B, which means you can't light the facade with a small flame. But in the case of a full-fledged fire, things change dramatically. It’s not easy to light a façade like that on fire, but if it goes wrong, the whole house can burn down.”
The fact that a house complies with all regulations says little about the actual likelihood of fire or the extent of damage
Legally covered
Fire safety regulations focus primarily on the safety of occupants and third-party property. They ensure that people can escape safely and that fire does not spread to other properties. “However, the fact that a house complies with all regulations says little about the actual likelihood of fire or the extent of damage,” Van Herpen argues. “The building itself may burn down completely; the regulations say nothing about that.”
In addition, regulations often lag behind innovations. “Regulations are drafted for traditional buildings; they don’t align with innovative developments,” he states. Developers and contractors, he says, deliberately don’t think beyond the regulations. “They don't think in a risk-oriented way. As long as they comply with the regulations, they are legally covered and they have nothing to blame if things go wrong.”
Van Herpen advocates a new approach where buildings not only comply with regulations, but are purposefully designed to minimize fire risks. “For each building, we should document fire safety, covering such areas as the reliability of fire compartmentation, smoke compartmentation, and load-bearing structures,” he says. This would also allow innovations such as bio-based materials and electrical systems to be safely integrated.
Bio-based materials
The use of bio-based building materials in sustainable construction, such as wood or straw, is increasing because of their lower environmental impact (CO2 emissions) and low weight. “For example, if three additional floors are built on top of an existing building, lightweight structures such as cross-laminated timber (CLT) or timber frame construction are ideal. Otherwise the foundation cannot support it,” says Van Herpen.
The disadvantage of these bio-based materials, however, is that they are flammable. Although there is plenty of time to escape, there is a good chance that the structure will burn down completely in the event of a fire. This, according to Van Herpen, raises a fundamental question: if a building is much more likely to burn down within its lifetime, exactly how sustainable is it?
Solar panels can be a major source of ignition, but that's because of the installation, not the panels themselves
Solar panels
Solar panels got a bad rap due to several fire incidents, are they really that dangerous? “Solar panels can be a major source of ignition, but that's because of the installation, not the panels themselves,” Van Herpen said. Wiring and connectors are especially risky. “If a plug starts sparking near a roof cavity with flammable material, things can go south real fast. Especially when you realize that on a sunny day the temperatures in the cavity under the solar panels rise to above 80 degrees Celsius.” With proper installation and maintenance, the risk of fire decreases significantly, he believes.
In traditional homes, solar panels are installed on the roof tiles, which is safer because the tiles provide protection. But in-roof solar panels, where the panels are integrated into the roof, lack this protection. Often there is a narrow cavity that cannot be properly ventilated, making it difficult for heat to dissipate. Underneath is only a waterproofing membrane and flammable insulation. This combination makes this set-up very risky, according to Van Herpen. He advocates a non-combustible material layer with some mass (for example, a cementitious board) under solar panels to reduce the risk.
As long as you have good mobility and can get out on your own in case of fire, the additional risk to your personal safety is not too bad
Aging and mobility
According to Van Herpen, people are not always aware of the risks of energy-efficient retrofitting and mainly look at the returns. If everything complies with regulations and a permit has been granted, they assume it's fine, even though that says nothing about the real fire risk. “As long as you have good mobility and can get out on your own in case of fire, the additional risk to your personal safety is not too bad, by the way,” he states.
This is why the mobility of building occupants is something that must be considered, he emphasizes. For example, seniors and people with physical disabilities are at much greater risk in the event of a fire. They need more time to get out or, in some cases, need help to do so. With the expected aging of the population in the coming decades, this vulnerable group will only get bigger, making it necessary to reduce the probability of buildings burning down.
Insurers are starting to sound the alarm now because they have to pay out more and more, but it’s actually too late already
Future
The increasing damage from fire, caused in part by innovative preservation techniques, shows that something needs to change soon, Van Herpen believes. “Insurers are starting to sound the alarm now because they have to pay out more and more, but it’s actually too late already,” says Van Herpen. Fire incidents – especially when there are casualties – ensure that a problem is taken seriously and, ultimately, addressed, but you want to be ahead of the curve. Still, Van Herpen is hopeful: “Slowly but surely, the issue is starting to receive more attention.”
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