ᐅ Questions About Wall Construction / New Single-Family House (Solid Construction)

Hello dear forum,

we are currently planning the construction of a solid single-family house with the following key details:

• Plot size: 417 sqm (4493 sq ft)
• Living area: approx. 155 sqm (1668 sq ft)
• Minimum KfW 70 standard
• Heating system: air-to-water heat pump (reasons: no gas connection possible, gas tank is rather undesirable / ground source heat via surface collectors is probably ruled out due to plot size / geothermal drilling possibly not allowed because of protected spring area)
• Federal state: Hesse

One question has been bothering us for quite some time now, namely the wall construction. We understand that there is no perfect brick or wall build and every building material has its own advantages and disadvantages. Precisely because of this, the decision is so difficult for us.

I would like to apologize in advance for any overly general or factually incorrect statements. We are certainly not experts in this field and appreciate every hint or suggestion .

The following points are important to us (as probably for everyone):
- Healthy indoor climate
- Good insulation values and as low heating costs as possible (future-oriented)
- Good sound insulation
- Good moisture resistance / low susceptibility to mold

At the moment, we favor Poroton. The properties of the brick seem reasonable to us, and this method is widely used in our region. Additionally, many local construction companies offer this building method as a standard. But here the difficulties begin. Often a standard is specified as a 17.5 cm (7 inch) brick plus 16 cm (6 inch) exterior thermal insulation composite system (ETICS) (e.g. rigid foam insulation boards or mineral wool), since this combination is said to meet the KfW standard most simply and cost-effectively. After extensive research (also here in the forum), we are still uncertain whether this approach is superior to a monolithic build or not. On the one hand, one hears about the advantages of ETICS, such as a lower risk of thermal bridges, but also about the disadvantages (poorer indoor climate, etc.).

Intuitively, we tend more towards a monolithic masonry with a 36.5 cm (14 inch) thick hollow brick (T8 or T9) without additional insulation. We expect this to provide a better indoor climate and better moisture protection (as mentioned, this might be a generalized misjudgment ). The KfW 70 standard can be achieved with the air-to-water heat pump in combination with both construction methods.

My specific questions are:

• Which wall construction is better suited for a new build and more future-oriented? Suitable alternatives to the ones described above are also welcome.
• If opting for an ETICS, which insulation material is recommended (I often read about polystyrene or mineral wool)?
• With which build is better insulation achieved (I assume with additional insulation)?
• Which construction method is more prone to defects and/or mold issues?
• Should a new build generally consider central or decentralized ventilation? Since we are both working full time during the day, prolonged and especially regular airing by opening windows is rather difficult and tends to be neglected after some time. If avoidable, we would also prefer to forego additional technical equipment (due to high acquisition costs and regular maintenance). On this point, I want to add that we have received very different opinions from various construction companies. Some claim that monolithic construction has a clear advantage in terms of moisture and air exchange and that additional ventilation systems are unnecessary. However, this seems too simplistic to me, as there is no such thing as a frequently cited “breathing wall.” Other builders solve this with decentralized ventilation or with ventilation slots in the windows (which are installed only after the blower door test – does it even make sense to test airtightness first and then add ventilation slots?).

Thank you very much in advance for your suggestions!!

You can find this exact discussion here https://www.hausbau-forum.de/threads/Wandaufbau-wie-habt-ihr-gebaut.10942/, and it is currently in full progress.

... of course, it is all a matter of cost ...

Hello,

you’re facing a really tough decision right now. We are also planning to build with Poroton T8 or T7. I see thermal insulation more as an option for retrofitting older buildings and personally don’t find it necessary with Poroton. I would rather choose a thicker, solid brick from the start.
We hope this will result in a better indoor climate and improved thermal insulation during summer! And personally, I just don’t like the idea of having plastic or polystyrene on the walls right from the beginning...
By the way, there is also insulation made from wood wool…
Edit: If you build completely solid now, there is still the option later on to add insulation on the exterior, in case standards change drastically. This is similar to what is often done with older buildings nowadays.

Regarding the different types of bricks, I can recommend the posts by Bauexperte in this thread:
https://www.hausbau-forum.de/threads/welche-massiv-wand.5825/

And on the topic of controlled ventilation, there are the following threads. We haven’t made a final decision yet on whether to install one and if so, which type. If we do, it will probably be a decentralized ventilation system simply because you don’t have long “ducts” that could potentially cause hygiene issues.
https://www.hausbau-forum.de/threads/Lüftung-nur-im-Fertighaus-holzstaender-mit-WDVS-oder-auch-im-Massivhaus.10624/
https://www.hausbau-forum.de/threads/so-schwer-die-Entscheidung-kwl-ja-nein.10645/
https://www.hausbau-forum.de/threads/kwl-mit-wrg-ein-verwirrspiel.10723/
https://www.hausbau-forum.de/threads/kontrollierte-be-und-Entlüftung-hygienische-Probleme-nach-5-6-Jahren.10867/
https://www.hausbau-forum.de/threads/kontrollierte-wohnraumlueftung-ja-oder-nein.3235/page-3#post-29751

I personally find ventilation slots in the windows pointless… Where is anything controlled there? It just causes drafts, like with old windows where the wind blows through from front to back…

Thank you for the responses!

@WildThing: Are the T7 and T8 bricks you mentioned solid bricks? There are countless different opinions on this topic as well. The question is whether the difference compared to a wall made with an uninsulated 36.5 cm (14.4 inches) hollow brick is really that significant. There is also a considerable cost difference here.

Of course, I want to avoid building a new house today (in this example with a 36.5 cm (14.4 inches) flat brick) that will require energy-efficient renovation in a few years – KfW 70 standard or not...

Regarding ventilation: From a cost-benefit perspective, a decentralized ventilation system would probably be the only option for us. I think we should do something since no one will be in the house between 7 a.m. and 6 p.m.

The T7 is only available filled, while the T8 comes filled or unfilled.
(We will probably choose the W08 or W07 from Leipfinger-Bader rather than from Schlagmann, but they are almost the same; only the filling differs.)

According to the brochure, whether filled or unfilled makes no difference for the U-value. Only the sound insulation changes between filled and unfilled versions. However, I cannot comment on the practical differences...

In the northern regions, brickwork is now also common... many constructions use cavity walls with insulation – including new builds. There are numerous insulation options available nowadays, ranging from polyurethane to flax or sheep wool – so from eco-friendly, comfortable materials to those that may emit gases.