ᐅ Alternatives to Polystyrene (External Thermal Insulation Composite Systems)?

Hello everyone,

We are currently building a KfW55 house with an exterior wall made of 24cm (9½ inches) solid sand-lime brick and 16cm (6¼ inches) ETICS insulation with a thermal conductivity of 0.035 W/(m·K). For cost reasons, polystyrene is planned as the insulation material for the ETICS.

If the weather cooperates, the insulation is scheduled to be installed in the next few weeks. The reinforcing mesh and the render will probably be applied later. This would at least protect the insulation before winter. However, I have heard that this might not be advisable. Although the insulation is supposed to be moisture-resistant, if it is not rendered immediately and it rains in the meantime, the insulation performance could decrease.

My question is whether this is true and if I can safely install the insulation now and apply the render later, or if it is better to do everything at once. The problem is that without insulation, the house would be exposed over the winter.

As a side question, while we're at it... Is there an alternative to polystyrene? I assume there is no comparable option unless you want to invest significantly more, but perhaps my information is outdated.

Cheers

First, check whether it is warm enough to bond the insulation. Our expert insisted on bonding at the beginning of October to ensure that the temperature was definitely high enough. My component temperature was at least 5°C (41°F).

The plaster was applied in January afterwards.

If you have concerns about later disposal, try searching for
Polystyrene + Fraunhofer + mealworms
and more likely
Polystyrene + Fraunhofer + recycling
or creasolv

Polystyrene contains raw materials and is therefore eventually too valuable to be incinerated.

You can also use stone wool, but it is more expensive. Alternatively, you can opt for a ventilated facade, which I always find to be the more attractive solution, but it is significantly more costly.

From an economic perspective, there is no practical alternative to polystyrene; one can have lengthy discussions about the pros and cons of mineral wool, stone wool, or other options, but personally, I would currently always choose polystyrene. When properly installed (which is crucial, as with almost everything!), it will outlast the rest of your house.

There is a useful study from the Fraunhofer Institute regarding external thermal insulation composite systems (ETICS), mostly based on polystyrene (can be found by searching online), with key findings (as far as I remember): fewer facade damages with ETICS facades compared to monolithic construction (the presumed reason being fewer thermal bridges, since there is a continuous insulation layer without real joints); almost no wear after XX years (I don’t recall the average age exactly, but I think it was somewhere between 25-40 years).

Thanks for the responses! From what I gather, using polystyrene in my situation actually works well, and it even has some advantages over monolithic construction that I wasn’t aware of.

It’s also not a problem to apply the insulation now and add the reinforcement later. Of course, this depends on the temperatures, but currently, we still have relatively mild days, and according to my measuring device, the walls are above 5°C (41°F) during the day. So if the weather looks good next week as well, I can install the polystyrene and have insulation in place for the winter. Once the temperatures allow, the reinforcement and so on can be applied.

It must not drop below that level at night either. Check the technical data for the duration and amount.
Here, it is cold, and I am waiting for snow.