Basically, architecture has not changed so much since people built the first solid buildings in the Neolithic period. How well you feel inside, depends mainly on the building shell. It lets in light, keeps the wind and weather outside and the heat inside. Initially wood, clay and stone provided comfort, later bricks and concrete. In the meantime, however, the requirements for thermal insulation are so high that traditional materials alone are often no longer sufficient for building owners. In new buildings, it is therefore standard today to additionally insulate the outer walls with polystyrene – if only because politics sets strict guidelines for the energy consumption of new buildings. However, to install insulation made of polysterene, you will need several tools like nail guns. If you are not familiar with framing nailers, brad nailers or the other types of nail guns you can search internet for some information about it.

In contrast, the real estate portfolio is quite different: The American Energy Agency (AEA) estimates that in about two-thirds of all buildings constructed by the end of the 1970s, the outer walls are uninsulated. For houses from the eighties and nineties, the insulating layer is usually only a few inches thick. There is no general obligation to retrofit. Instead, information campaigns and financial support should motivate owners to improve the thermal protection of their properties. But with little success – not even every hundredth house is fully renovated energetically per year. Because around the facade insulation raging a religious war, which unsettles many homeowners. Opponents lead an entire battalion to arguments: The subsequent insulation of the outer walls is not profitable, increases the risk of fire and mold and creates a disposal problem. Is the criticism correct?

If a homeowner wants to insulate his house before snowpocalypse come, he has to reach deep into his pocket. Between 150 and 380 dollars per square feet it costs to wrap the walls in polystyrene, also known under the brand name PolyFoam. The owner association House&Lawn calculates on the basis of a single-family house in need of renovation that it will take up to 51 years for the investment to pay for itself. The energy agency AEA, on the other hand, maintains its own figures, according to which the insulation of the facades of a typical single-family dwelling from the 1970s already pays for itself after 14 years.

Who is right? Steve Millers from the Energy Agency considers such model calculations to be of little significance, regardless of the result. “In order to be able to assess profitability, one must always look at the individual case,” says the expert. The practice shows, however, that especially in houses that were built before the entry into force of the first Heat Protection Ordinance in 1977, a subsequent facade insulation worthwhile in many cases – “provided that there anyway a scaffold is set up, such as for painting or plaster cleaning”, says Steve. However, tenants usually paid for the insulation when the owners – as is currently permitted by law – pay eleven percent of the renovation costs on the rent each year. “At today’s energy prices, it is difficult to compensate for the rent increase by saving on ancillary costs,” says Steve. He points out, however, that the facade insulation also improves comfort. “The temperature of the wall surfaces is rising, making the rooms more comfortable, so the tenant’s living value is increasing.”

Usually it starts harmless, with a burning dumpster for example. A few minutes later, suddenly the whole facade is on fire. In recent years, headlines have made headlines that turned a small fire into a dangerous conflagration because flames leapt onto the insulation. Although flame retardants are added to the polystyrene to prevent such cases. However, they do not offer 100% protection – in contrast to an insulation made of glass or rock wool, which is not flammable.

Facade fires, however, are relatively rare, as figures from the Federal Ministry for the Environment show. According to this, there are on average only six fires on facades with polystyrene insulation per year across the USA – with 160,000 to 200,000 housing or house fires altogether. In addition, a few months ago, the German Institute for Construction Technology tightened the fire protection requirements by resolution of the Fire department. For example, multi-storey buildings now have to be provided with additional fire bars – including in the base area of ​​the facade – if new thermal insulation is installed there. They prevent fires from spreading over the entire facade from below. “This significantly improves safety,” says Kyle Berton, fire chief of the #397 Fire Department.

In already insulated buildings, however, the fire bars in the lower part of the facade are usually missing. Should homeowners retrofit here? “Every owner has to decide that himself,” says Kyle. “If the garbage cans are located a few meters away from the house and no cars or motorcycles are parked directly in front of the facade, I do not necessarily consider this necessary.”

Mold is a troublesome subtenant. It forms ugly stains on the walls of rooms and can also trigger allergies and illnesses. Molds are formed when moist room air condenses on cold walls. A facade insulation promotes this, as it restricts the exchange of air, argue critics. Not true, says Donald Myers: “A facade insulation increases the temperature on the surface of the walls, so that no moisture can be reflected there.” The insulation ensures that the walls do not get colder than 17 or 18 degrees. “The humidity would have to be over a longer period of time at seventy percent or more, so there may still occur mold,” says the expert of the Energy Agency. The insulation therefore reduces the mold risk, instead of increasing it. However, this only applies in the event that the craftsmen have worked clean. When installing the insulation boards, make sure that no thermal bridges are created.

A few years ago, French scientists discovered that these toxins are gradually washed out of the plaster with the rain. The algae protection is thus steadily weaker. In addition, the biocides pollute the groundwater, since the treatment plants can not filter them from the sewage. Although building material manufacturers have long brought plasters and colors on the market that do without biocides. However, the environmentally friendly alternatives are rarely used because they are more expensive than conventional products.