ᐅ Is mechanical ventilation with heat recovery necessary for lightweight expanded clay aggregate construction and KfW55 standard homes?
Created on: 19 May 2021 07:34
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Matthias_1212
Dear forum community,
After finding a plot of land, we now need to specify the technical building services.
We want to build a KFW55 house with a heat pump. So far, so good. After reading extensively in the forum, I was fairly certain that we would need a central mechanical ventilation with heat recovery system (MVHR), since we both work full-time in an office and probably won’t be able to regularly ventilate by opening the windows for air and moisture exchange.
Our builder believes that a central mechanical ventilation system is not necessary with his construction method because he uses expanded clay aggregate blocks. Additionally, he installs a controlled ventilation system integrated in the windows. According to him, a mechanical ventilation system is only installed—if at all—in about one house per year out of more than 100 houses built annually. He thinks the situation would be different with Ytong blocks, where a mechanical ventilation system is always necessary.
If we insist on a mechanical ventilation system, the additional costs would be around €15,000 for the unit (Pluggit) and €8,000 for raising the walls and screed on the upper floor—in total €23,000. From the reports here in the forum, I consider this surcharge to be very high.
Our builder uses expanded clay aggregate blocks. The wall structure is roughly:
- 15cm (6 inches) expanded clay aggregate
- 19cm (7.5 inches) insulation
- vapor barrier and exterior plaster
Total wall thickness: approximately 35cm (14 inches)
I am unable to assess the builder’s statements. Is it true that with expanded clay aggregate blocks a mechanical ventilation system is not needed due to their favorable moisture regulation properties?
I would be very grateful for your help.
Best regards,
Matthias
After finding a plot of land, we now need to specify the technical building services.
We want to build a KFW55 house with a heat pump. So far, so good. After reading extensively in the forum, I was fairly certain that we would need a central mechanical ventilation with heat recovery system (MVHR), since we both work full-time in an office and probably won’t be able to regularly ventilate by opening the windows for air and moisture exchange.
Our builder believes that a central mechanical ventilation system is not necessary with his construction method because he uses expanded clay aggregate blocks. Additionally, he installs a controlled ventilation system integrated in the windows. According to him, a mechanical ventilation system is only installed—if at all—in about one house per year out of more than 100 houses built annually. He thinks the situation would be different with Ytong blocks, where a mechanical ventilation system is always necessary.
If we insist on a mechanical ventilation system, the additional costs would be around €15,000 for the unit (Pluggit) and €8,000 for raising the walls and screed on the upper floor—in total €23,000. From the reports here in the forum, I consider this surcharge to be very high.
Our builder uses expanded clay aggregate blocks. The wall structure is roughly:
- 15cm (6 inches) expanded clay aggregate
- 19cm (7.5 inches) insulation
- vapor barrier and exterior plaster
Total wall thickness: approximately 35cm (14 inches)
I am unable to assess the builder’s statements. Is it true that with expanded clay aggregate blocks a mechanical ventilation system is not needed due to their favorable moisture regulation properties?
I would be very grateful for your help.
Best regards,
Matthias
Schimi179119 May 2021 10:01Bookstar schrieb:
Just take a moment to think about what the developer is saying there. And dismiss the whole story as complete nonsense. Of course, it’s nonsense—what role would the masonry play? However, if you plan to install a pink toilet bowl, then the mechanical ventilation system could probably be omitted. And you’d think, "they know what they’re doing."
(to refer to the attic in the neighboring thread)
Matthias_1212 schrieb:
If we still insist on a mechanical ventilation with heat recovery system, the additional costs amount to approximately €15,000 for the unit (Pluggit) and €8,000 for raising the walls and the screed on the upper floor. P.S.: I hope you are mistakenly using the term "developer" and actually mean a general contractor (GC) whom you can choose freely. Maybe this builder only works with that one wall construction and only knows about other methods by hearsay?
I interpret the "raising of the walls" as a complete lack of knowledge regarding mechanical ventilation with heat recovery (their ceiling supplier probably can’t handle it, so they need extra height on the floor for the ductwork, meaning they only know about central mechanical ventilation systems from hearsay). Since, based on your own assessment, you have diagnosed the need for either a trickle vent or mechanical ventilation with heat recovery—one of the two is definitely necessary—I advise you to change the builder. They obviously lack expertise. Or is it even more than one area?
Schimi1791 schrieb:
And here you think, "they know what they’re doing."
(to point to the attic topic in the neighboring thread) Could you please share the post number? I couldn’t find it in the other thread started by the original poster.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
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Matthias_121219 May 2021 10:1611ant schrieb:
P.S.: I hope you are mistaken in your use of the term "developer" and actually mean a general contractor (GC) whom you can choose freely. No, the term "developer" is used correctly. In this specific case, there is no choice due to the plot of land.
Matthias_1212 schrieb:
No, the term developer is correctly used. In this specific case, there is no choice due to the plot of land. Oh dear, I feel sorry for you. It’s unfortunate when you have to make a general contractor understand their responsibilities only with the help of an expert. Then you have to take this general contractor because they are unfortunately also the developer, and make the best out of it: expanded clay aggregate is acceptable, external thermal insulation composite systems (ETICS) are, as you know, not my favorite but there are worse setbacks than this, and apparently you need to avoid centralized mechanical ventilation with heat recovery with them. In my view (which needs to be personally clarified by you since there are no absolute truths here), the decision is whether you prefer a standard ventilation system or a decentralized mechanical ventilation with heat recovery.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
M
Matthias_121219 May 2021 10:2911ant schrieb:
I see the trade-off (which, in my opinion, can only be decided by you personally since there are no absolute truths) as whether you want RegelAir or decentralized controlled residential ventilation. That’s what I feared. I can only partially warm up to either option.
With decentralized controlled residential ventilation, I would have several core drillings through the insulation. Is heat recovery and filtration even possible with this option?
With window frame ventilation (RegelAir), I have some reservations about cutting into the brand-new window seals.
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