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
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nordanney19 May 2021 14:23Bookstar schrieb:
Decentralized is absolutely unsatisfactory.Please tell the original poster why. Bookstar schrieb:
Also leave out the window rebate things.I agree with that as well.
Nowadays, I wouldn’t build without ventilation. However, it’s an old debate... I’ve just spent a lot of money installing decentralized ventilation systems in an existing building. The CO2 levels in the bedroom and humidity in the bathroom were simply too high... But I hear there are also people who leave bedroom doors open at night for children and cats...
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nordanney19 May 2021 15:09lastdrop schrieb:
But there are people who leave bedroom doors open at nightOf course, the bedroom door stays open. Other than not letting the children overhear what the parents are up to 😉 or keeping pets out, is there any reason to close the bedroom door?nordanney schrieb:
Please tell the original poster why.
I agree with that. A little research is enough for that. There is plenty of information available on this. There is a reason why most people turn those things off. They are simply too expensive.
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