We are planning a new build as an energy-efficient house according to the Energy Saving Ordinance, KfW70 standard. The developer claims that with very good insulation, solar thermal systems, and a condensing boiler, etc., this can be achieved without mechanical ventilation. A new build is sealed quite tightly as verified by a blower door test. The developer says we do not need to worry about moisture problems.
We are also used to regular manual ventilation from living in our old house... However, there the cold, fogged-up window was a reliable indicator...
The additional costs for a ventilation system would be significant...
What do the experts here think? Is it better not to forgo such a system, or does it not matter? I do not want to suffocate at night or discover mold after two years...
We are also used to regular manual ventilation from living in our old house... However, there the cold, fogged-up window was a reliable indicator...
The additional costs for a ventilation system would be significant...
What do the experts here think? Is it better not to forgo such a system, or does it not matter? I do not want to suffocate at night or discover mold after two years...
R
ralph1234518 May 2010 13:43PenK schrieb:
The ventilation system saves about 12 to 18 kWh/m²/a at an efficiency of 80% (90% is already achievable), with a self-consumption of around 4.5 kWh/m²/a. Wow. Assuming a gas price of 4.5 cents per kWh and an electricity price of 16 cents per kWh, which is rather low, financially this is a break-even scenario despite investments of around €9000. That means economically there is initially no benefit. For this to improve, electricity prices must fall, gas prices must rise, and the apartment must be warm enough so that heating energy consumption increases... €9000 already creates an interest burden of €340 per year during construction.
And regarding CO2 savings?... If the electricity is generated with a power plant efficiency of 40%, then 4.5/40% = 11 kWh of primary energy is needed to save back 12-18 kWh, with an optimal difference of 18-11 = 7 kWh, multiplied by 160 m² (1722 sq ft) = 1120 kWh. Well, at least that.
The crucial question remains whether this is really necessary to avoid moisture problems.
Had a brief conversation this morning with an expert who said that even among professionals opinions differ on this, as the overall experience is still quite limited, especially regarding long-term statements.
Gartenbau schrieb:
The crucial question remains whether this is truly necessary to avoid moisture problems.
We had a brief conversation this morning with an expert who said that even among professionals opinions differ, as the overall experience is still quite limited, especially regarding long-term effects. That is the issue. I would always recommend ventilation for airtight walls such as calcium silicate, porcelain blocks with polystyrene insulation, prefabricated houses with OSB walls, or windproof membranes. Ventilation is not necessary for vapor-permeable walls such as aerated concrete (Ytong, Hebel), 36 cm (14 inches) porcelain blocks without external insulation, or prefabricated houses with a specialized wall structure without membrane. These walls allow the house to "breathe," and if there is good ventilation—as in airing throughout the night—everything is fine.
PenK schrieb:
That’s the issue. I would always recommend ventilation for vapor-tight walls such as calcium silicate blocks, Poroton with polystyrene insulation, prefabricated houses with OSB walls or windproof membranes. Ventilation is not necessary for vapor-permeable walls like Ytong, Hebel, 36cm (14 inch) Poroton without external insulation, or prefabricated houses with a special wall structure without membrane. In these cases, the house can "breathe," and if there is good ventilation, for example throughout the night, then everything is fine. The idea that houses or walls can "breathe" is a myth that keeps being spread without any basis in reality! Before making such a statement, one should have a solid understanding of building physics!
Regards
Are all the others stupid?
What is your problem with answers from other forum members? Just answer the question and that’s it. Don’t make the person asking look like an idiot who is too dumb to judge for themselves!
€uro schrieb:
Before making a statement like that, you should have a more solid understanding of building physics!
Regards
What is your problem with answers from other forum members? Just answer the question and that’s it. Don’t make the person asking look like an idiot who is too dumb to judge for themselves!
R
ralph1234518 May 2010 17:12First of all, diffusion and breathing are two different things.
A wall could be air-permeable, which would require it to be thin and porous or full of holes; this is generally not the case with typical walls. Diffusion occurs when it is not hindered by building materials like concrete or membranes, but diffusion—especially through thick walls—is a slow process that, in my humble opinion, is not suitable for continually removing large amounts of moisture.
What remains is the air exchange through door gaps, window leaks, etc., which is also required by energy efficiency regulations to keep CO2 and O2 levels in the indoor air at acceptable levels. The blower door test does not achieve a value of zero air leakage. The question is whether this air exchange, combined with normal ventilation habits, is still sufficient to keep moisture out.
There are quite a few reports online from people who have built without controlled mechanical ventilation and do not all report mold problems in their homes.
PS - It should be possible for two people to hold different opinions here without it becoming personal...?
A wall could be air-permeable, which would require it to be thin and porous or full of holes; this is generally not the case with typical walls. Diffusion occurs when it is not hindered by building materials like concrete or membranes, but diffusion—especially through thick walls—is a slow process that, in my humble opinion, is not suitable for continually removing large amounts of moisture.
What remains is the air exchange through door gaps, window leaks, etc., which is also required by energy efficiency regulations to keep CO2 and O2 levels in the indoor air at acceptable levels. The blower door test does not achieve a value of zero air leakage. The question is whether this air exchange, combined with normal ventilation habits, is still sufficient to keep moisture out.
There are quite a few reports online from people who have built without controlled mechanical ventilation and do not all report mold problems in their homes.
PS - It should be possible for two people to hold different opinions here without it becoming personal...?
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