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
M
Matthias_1212M
Matthias_121219 May 2021 07:34Dear 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
In our case, the controlled residential ventilation system from Bosch (the ground-source heat pump is also from Bosch) costs an additional 12,000 to a maximum of 13,000 euros. However, we are building in monolithic construction, a bungalow, with a ceiling height of 3 meters (10 feet) excluding the raised floor.
Our general contractor initially also thought that controlled residential ventilation was not necessary. After a long back and forth, we decided to go for it.
Our general contractor initially also thought that controlled residential ventilation was not necessary. After a long back and forth, we decided to go for it.
Just take a moment to think about what the developer is saying. And dismiss the whole story as complete nonsense. Of course, it’s nonsense—what role could the masonry possibly play? However, if you plan to install a pink toilet bowl, then the mechanical ventilation system probably isn’t necessary.
Bookstar schrieb:
Just take a moment to think about what the developer is saying. And dismiss the whole story as complete nonsense. Of course, it doesn’t make sense—what role would the masonry play? However, if you are planning a pink toilet bowl, then controlled mechanical ventilation might be unnecessary.What? Have you never heard of breathable walls? 😎
The statement regarding the wall construction is overall certainly nonsense.
His conclusion that the centralized mechanical ventilation with heat recovery in his houses is unnecessary is likely not based on the wall construction itself, but on the installed "Regel-Air-System." Whatever exactly that entails in detail.
It is obvious that the developer simply cannot offer or implement a mechanical ventilation system with heat recovery at a reasonable price with his construction method and therefore advises against it. At least, that is probably the reason why only one out of a hundred of his clients opts for the mechanical ventilation system with heat recovery. Nothing more.
His conclusion that the centralized mechanical ventilation with heat recovery in his houses is unnecessary is likely not based on the wall construction itself, but on the installed "Regel-Air-System." Whatever exactly that entails in detail.
It is obvious that the developer simply cannot offer or implement a mechanical ventilation system with heat recovery at a reasonable price with his construction method and therefore advises against it. At least, that is probably the reason why only one out of a hundred of his clients opts for the mechanical ventilation system with heat recovery. Nothing more.
Matthias_1212 schrieb:
Our builder uses expanded clay aggregate. The wall structure is roughly:
- 15cm (6 inches) expanded clay aggregate
- 19cm (7.5 inches) insulation I would rather phrase it as: "builds ETICS (External Thermal Insulation Composite System) using an expanded clay load-bearing shell." But regarding your main question: I can only agree with @Bookstar, hardly anything makes less sense. @Nordlys has window vents and monolithic aerated concrete; I don’t see the difference between a gas boiler and a heat pump as relevant for controlled mechanical ventilation. What matters most is your honest self-assessment that you won’t be able to ventilate regularly in everyday life. If that’s the case, you need one of the two systems to manage it for you—and in my opinion, it’s your personal “philosophical” choice whether that should be window vents or controlled mechanical ventilation. You should apparently take your builder’s technical opinions with caution; this usually applies equally in all areas.
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