Hi,
we spoke with our builder regarding upgrading our KfW70 project to KfW55.
I would like a “real” KfW55, meaning actual savings in energy consumption, not just adjusted calculations.
For me, this means we need to improve insulation and the masonry.
Currently, the plan is:
KfW70 house built in solid construction, single-layer masonry without extra polystyrene insulation, built with Poroton T9 bricks 36.5cm (14.4 inches) thick (not filled) with a U-value of 0.23 as far as I know. The slab foundation and basement will be insulated, triple-glazed windows, air-to-water heat pump, flat roof with solid ceiling, extensively greened.
I thought that since the foundation slab is already insulated and we have triple-glazed windows, the additional work might not be so extensive. But we were told to expect about €30,000 in extra costs because we need thicker bricks (42.5cm / 16.7 inches) and mechanical ventilation with heat recovery. However, I have seen that the T9 brick is sufficient for KfW55, or at least a T8 at 36.5cm (14.4 inches) — T7 would be even better. The price increase per 1,000 bricks would be around €800–1,000 depending on the brick. That would already give us a much better exterior wall, wouldn’t it?
I have not found anything that says you absolutely need mechanical ventilation, which I actually want to avoid.
Somewhere I also read that the extra cost should settle around €7,000–8,000 to go from KfW70 to KfW55. Can anyone confirm that?
Who can reliably tell me what exactly I need to upgrade from the current planned standard to KfW55? And as I said, not with adjusted calculations because instead of the heat pump, we would use wood pellets. I’m really interested in reducing the primary energy demand.
Thanks in advance
we spoke with our builder regarding upgrading our KfW70 project to KfW55.
I would like a “real” KfW55, meaning actual savings in energy consumption, not just adjusted calculations.
For me, this means we need to improve insulation and the masonry.
Currently, the plan is:
KfW70 house built in solid construction, single-layer masonry without extra polystyrene insulation, built with Poroton T9 bricks 36.5cm (14.4 inches) thick (not filled) with a U-value of 0.23 as far as I know. The slab foundation and basement will be insulated, triple-glazed windows, air-to-water heat pump, flat roof with solid ceiling, extensively greened.
I thought that since the foundation slab is already insulated and we have triple-glazed windows, the additional work might not be so extensive. But we were told to expect about €30,000 in extra costs because we need thicker bricks (42.5cm / 16.7 inches) and mechanical ventilation with heat recovery. However, I have seen that the T9 brick is sufficient for KfW55, or at least a T8 at 36.5cm (14.4 inches) — T7 would be even better. The price increase per 1,000 bricks would be around €800–1,000 depending on the brick. That would already give us a much better exterior wall, wouldn’t it?
I have not found anything that says you absolutely need mechanical ventilation, which I actually want to avoid.
Somewhere I also read that the extra cost should settle around €7,000–8,000 to go from KfW70 to KfW55. Can anyone confirm that?
Who can reliably tell me what exactly I need to upgrade from the current planned standard to KfW55? And as I said, not with adjusted calculations because instead of the heat pump, we would use wood pellets. I’m really interested in reducing the primary energy demand.
Thanks in advance
KfW is just about making the numbers look better. Better quality bricks don’t matter much if you don’t have more insulation. It’s the many individual components that improve the overall efficiency multiplier. For example, the ventilation system mentioned, warm edge spacers in the windows, better window orientation (south!), fewer windows, better front door insulation, or your pellet heating system.
In the end, you have to see what’s really worth it. KfW 55 is usually only done to qualify for subsidies. You don’t really save much on heating costs, or at best you recover the additional costs over 20 years. Much more important is to make good use of the combination of options in terms of price-performance ratio (for example, we have 18 cm (7 inches) of insulation in the walls) and avoid thermal bridges (no warm edge spacer in the windows). A ventilation system is nowadays almost always a good idea.
PS: In 10 years (before that, selling a house is generally not financially sensible), no one will care whether the house is KfW 55 or 70. By then, it will be outdated, like insulation technology from the year 2000.
In the end, you have to see what’s really worth it. KfW 55 is usually only done to qualify for subsidies. You don’t really save much on heating costs, or at best you recover the additional costs over 20 years. Much more important is to make good use of the combination of options in terms of price-performance ratio (for example, we have 18 cm (7 inches) of insulation in the walls) and avoid thermal bridges (no warm edge spacer in the windows). A ventilation system is nowadays almost always a good idea.
PS: In 10 years (before that, selling a house is generally not financially sensible), no one will care whether the house is KfW 55 or 70. By then, it will be outdated, like insulation technology from the year 2000.
xycrazy schrieb:
Hi,
Who can reliably tell me what I need to upgrade from the currently planned standard to KFW55? And as I said, not just a nice calculation since wood pellets will be used instead of a heat pump. I’m really focused on reducing the primary energy demand.
Thanks in advanceHello,
Only your building energy consultant, architect, or builder can truly advise you based on your specific house requirements.
You want to reduce the primary energy demand but consider switching to pellets not effective?
Olli
B
Bauexperte16 Aug 2015 23:11xycrazy schrieb:
Now I was thinking... And I thought you would fill out your profile in the near future...!
xycrazy schrieb:
... due to the already insulated concrete slab and triple-glazed windows, the effort shouldn’t be that great anymore. That’s the eternal debate about faith and facts.
If I could see where you plan to build, I might be able to assess the roughly 30,000 euros mentioned. You already know that your current plan won’t be sufficient.
Regards, Bauexperte
Similar topics