Surcharge from KFW70 to KFW55 = 30,000€???

Hi,

we spoke with our builder regarding the Kfw55 upgrade of our Kfw70 construction project. I would like a "real" KFW55... meaning with actual energy savings, not artificially calculated. For me, this means we need to improve insulation and masonry.

Currently, the following is planned:

KFW70 house built in solid construction, single-shell masonry, without extra Styrofoam insulation, built with Poroton T9 bricks 36.5cm (not filled) with a U-value of 0.23 to my knowledge. The floor slab is insulated, the basement as well, triple-glazed windows, air-water heat pump, flat roof with solid ceiling, extensively greened.

Now I thought that due to the already insulated floor slab and the triple-glazed windows, the effort shouldn’t be that great anymore. But we were told that we have to calculate about €30,000 in additional costs because we need thicker bricks (42.5cm) and mechanical ventilation. However, I have seen that the T9 is also sufficient for KFW55, or at least a T8 in 36.5cm – T7 would be even better. The extra cost per 1000 bricks would be €800-1000 depending on the brick. That would already give us a significantly better exterior wall, right?

I haven’t found anywhere that a controlled mechanical ventilation system is absolutely necessary, which I would actually like to avoid.

Somewhere I also read that the effort should settle somewhere between €7,000-8,000 to go from KFW70 to KFW55. Can someone confirm that?

Who can reliably tell me what I need to get from the currently planned standard to KFW55? And as I said, no artificially calculated figures because instead of a heat pump, wood pellets will be used. My real goal is to reduce the primary energy demand.

Thanks in advance

kfw is just window dressing. some supposedly better bricks are nonsense, if anything more insulation matters. it’s the many individual components everywhere that improve the multiplier. for example, the mentioned ventilation system or warm edge on the windows or better window orientation (south!) or fewer windows or better front door insulation or your pellet heating.

in the end, you have to see what’s really worth it. you only do KFW 55 to get the subsidy. you don’t save real heating costs or if you do, you at best recover the extra costs in 20 years. much more important is to make good use of the sum of possibilities in terms of price-performance ratio (for example, we have 18cm insulation in the wall) and to avoid thermal bridges (no warm edge in the window). a ventilation system makes sense nowadays almost always.

ps: in 10 years (before that a house sale is actually never financially sensible) no one will care if the house is KfW 55 or 70. then it will be outdated like the insulation technology from the year 2000.

Hi,


Who can reliably tell me what I need to move from the currently planned standard to KFW55. And as I said, not nicely calculated because instead of a heat pump, wood pellets will be used. I really want to reduce the primary energy demand.

Thanks in advance

Good morning

Only your building energy consultant, architect, or builder can really tell you that based on your exact wishes for the house.

You really want to reduce the primary energy demand, but consider switching to pellets unproductive?


Olli

Now I was thinking ...

And I thought you would fill out your profile in the near future ...!

... due to the already insulated floor slab and the triple-glazed windows, the effort should not be that great anymore.

That’s the eternal issue with faith and church.

If I could see now where you want to build, I might be able to estimate the EUR 30k in question. You already know that you won’t make it with the current planning.

Rhenish regards