KFW 55 / Decentralized Ventilation / Exterior Wall

Dear builders, As a layperson in the construction field, we signed our house contract last week. Single-family house 146 sqm living space, aerated concrete 36 cm, air heat pump, 1.5 stories, hipped roof, facing south. House price approx. 260,000 Now I have read intensively into the KFW standards and I am completely unsure whether to commission a KFW expert to calculate for me whether KFW 55 can be achieved and with how much additional effort. If this is under 18,000 or just above, then it would be sensible to do it. My consideration is whether to use decentralized ventilation room by room (bathrooms, utility room, pantry). I really don’t know how to proceed. We are building through a developer who apparently does not think much of extra insulation, etc. Difficult

And why no central controlled residential ventilation?

The question is first whether I go for the KFW 55. The question why no central controlled residential ventilation is good. We actually like to ventilate, so I would have installed ventilation only in the rooms mentioned above, probably also cheaper in terms of cost. It doesn't matter if a noise is heard there sometimes etc.

One should have given it some thought before signing. Controlled residential ventilation only central, decentralized is an emergency solution for renovations.

My developer has probably never installed a system like this either, at least it was never mentioned in the preliminary discussions. I find that a bit disappointing

You can also gladly and frequently ventilate additionally with a controlled residential ventilation system (regardless of the type). But there is a difference whether you ventilate a 100+ sqm house manually or an apartment. (However, of course I don’t know what kind of residential properties you have lived in so far)

probably has never installed such a system,

Well, there is always a first time for everything and it’s not rocket science.