Hello, we plan to start building our own home this year.
I already have two active discussion threads on this forum about it.
https://www.hausbau-forum.de/threads/Hausbau-kfw70-ca-150m-welche-Heizung-Gas-lwwp.12261/
https://www.hausbau-forum.de/threads/wir-wollen-bauen-ist-das-was-uns-angeboten-wird-so-i-o.12269/
We just got back from discussing the offer with the supplier.
I tried to talk about heating and ventilation; he shared his experiences, opinions, and advice.
This didn’t quite match what I had read so far, so now I’m uncertain and confused again.
We requested a 150m² (1,615 sq ft) solid house built to KFW 70 standard.
This is achieved through insulation and a gas-solar heating system. More details are in my other threads.
When I asked about a mechanical ventilation system with heat recovery, he said it’s not needed, that regular airing is sufficient.
He also said his son built a KFW 70 house with gas-solar three years ago and that he would never do that again. Better to build without KFW 70, save the money for the energy certificate inspection and the solar system (about 5,000), keep the insulation as is, and move on. Apparently, it’s not financially worthwhile.
Regarding the wall construction, another supplier told me the following:
Me: Is there an air gap between the insulation on the masonry and the facing brick?
He: Yes, of course, we don’t list that separately because it’s required by DIN (German industrial standards).
Today, with our current supplier:
Me: Is there an air gap between the insulation on the masonry and the facing brick?
He: No, that’s a cavity insulation. That might have been necessary in the past, but with today’s insulation materials, it’s no longer needed.
So what is correct? Is an air gap between the insulation and masonry required by DIN, or does it depend on which insulation material is used?
I already have two active discussion threads on this forum about it.
https://www.hausbau-forum.de/threads/Hausbau-kfw70-ca-150m-welche-Heizung-Gas-lwwp.12261/
https://www.hausbau-forum.de/threads/wir-wollen-bauen-ist-das-was-uns-angeboten-wird-so-i-o.12269/
We just got back from discussing the offer with the supplier.
I tried to talk about heating and ventilation; he shared his experiences, opinions, and advice.
This didn’t quite match what I had read so far, so now I’m uncertain and confused again.
We requested a 150m² (1,615 sq ft) solid house built to KFW 70 standard.
This is achieved through insulation and a gas-solar heating system. More details are in my other threads.
When I asked about a mechanical ventilation system with heat recovery, he said it’s not needed, that regular airing is sufficient.
He also said his son built a KFW 70 house with gas-solar three years ago and that he would never do that again. Better to build without KFW 70, save the money for the energy certificate inspection and the solar system (about 5,000), keep the insulation as is, and move on. Apparently, it’s not financially worthwhile.
Regarding the wall construction, another supplier told me the following:
Me: Is there an air gap between the insulation on the masonry and the facing brick?
He: Yes, of course, we don’t list that separately because it’s required by DIN (German industrial standards).
Today, with our current supplier:
Me: Is there an air gap between the insulation on the masonry and the facing brick?
He: No, that’s a cavity insulation. That might have been necessary in the past, but with today’s insulation materials, it’s no longer needed.
So what is correct? Is an air gap between the insulation and masonry required by DIN, or does it depend on which insulation material is used?
EveundGerd24 Apr 2015 15:34Why insulation instead of a thicker Poroton brick?
An architect I recently spoke with said that this is the best approach. Because the reinforced concrete slab still settles slightly, the bricks develop cracks. If the bricks only have a plaster layer, these cracks will also appear in the plaster facade. However, if insulation is installed over the bricks, the cracks in the bricks are not visible.
I have no idea if this makes sense or if it is indeed the case, but the construction company is building it this way for us.
I have no idea if this makes sense or if it is indeed the case, but the construction company is building it this way for us.
If you choose aerated concrete as your masonry unit, you can consistently use the 365 mm (14.4 inches) size.
I believe many suppliers not only sell the material but also partly the reassurance that it complies with KfW standards.
The additional cost for some insulation is never anywhere near 7,000 euros – unless the wall construction type changes.
Triple-glazed windows can mean a lot of different things, and I find that term vague unless you also have the energy performance certificate calculation at the same time—that will specify exactly what you’re getting.
For example: triple glazing could mean a frame heat transfer coefficient (Uf) of 1.3 and a glass heat transfer coefficient (Ug) of 0.7, or a Uf of 0.78 with a Ug of 0.5.
For a typical double window measuring 1.76 m by 1.34 m (5.8 ft by 4.4 ft) with a 5 cm (2 inch) frame, this results in 2.18 m² (23.5 ft²) of glass and 0.58 m² (6.2 ft²) of frame area. That means either a heat loss of 73 W (at -12°C (10°F) outside and 20°C (68°F) inside) or 49 W… so a difference of roughly 30%. When you consider that the KfW 70 standard for primary energy demand means you’re only 30% below the limit, that’s quite significant.
I believe many suppliers not only sell the material but also partly the reassurance that it complies with KfW standards.
The additional cost for some insulation is never anywhere near 7,000 euros – unless the wall construction type changes.
Triple-glazed windows can mean a lot of different things, and I find that term vague unless you also have the energy performance certificate calculation at the same time—that will specify exactly what you’re getting.
For example: triple glazing could mean a frame heat transfer coefficient (Uf) of 1.3 and a glass heat transfer coefficient (Ug) of 0.7, or a Uf of 0.78 with a Ug of 0.5.
For a typical double window measuring 1.76 m by 1.34 m (5.8 ft by 4.4 ft) with a 5 cm (2 inch) frame, this results in 2.18 m² (23.5 ft²) of glass and 0.58 m² (6.2 ft²) of frame area. That means either a heat loss of 73 W (at -12°C (10°F) outside and 20°C (68°F) inside) or 49 W… so a difference of roughly 30%. When you consider that the KfW 70 standard for primary energy demand means you’re only 30% below the limit, that’s quite significant.
EveundGerd25 Apr 2015 20:45I find the statement about the cracks in the stones rather strange.
What about the interior plaster then? It should actually develop cracks even more easily since it is applied much thinner and without a base coat directly onto the stones.
I believe the company simply builds this way and uses this somewhat odd argument to justify it.
What about the interior plaster then? It should actually develop cracks even more easily since it is applied much thinner and without a base coat directly onto the stones.
I believe the company simply builds this way and uses this somewhat odd argument to justify it.
Passivhaus schrieb:
We are building a timber frame house. It will be insulated with cellulose. According to our architect/energy consultant, this will easily achieve KfW55 standard and be quite "green" thanks to renewable raw materials.
A traditional masonry builder we consulted with already rolled his eyes when we mentioned KfW70. With timber houses, achieving good insulation might actually be easier.It is equally feasible with a 49cm (19 inch) Poroton block, even without seven layers of additional cladding plus seven times extra work, ventilated cavities, OSB boards, spruce planks, and drywall mania at cubic meter prices beyond reasonable limits, over 700 euros and up.
Apply a mineral plaster on the outside of the 49cm (19 inch) solid brick, a clay plaster on the inside, and use quality window materials with Uf 0.78 + Ug 0.5 W/m²K values, and you are already close to passive house standard.
The cubic meter price of the brick is about 80 euros including adhesive, external plaster, and internal clay plaster.
The wooden construction costs four times as much as a brick construction and only offers roughly comparable performance.
Is a brick house really green enough...?
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