Of course the house develops, you should take enough time for that! Today we are pouring the floor slab and we are still tinkering with planning details. Such an important consideration, like for example taking an elderly woman into the house, should really already be properly taken into account now. A successful life/house project arises not only through the correct, technical construction but also through the later satisfaction of ALL involved. In the next life I’ll probably be a philosopher. :D
At least plan for the mother-in-law topic so that on day X it can be implemented without massive/expensive interventions, or just leave it. But better don’t reassure yourself with “We’ll somehow manage that then.” I think that in some conversations with an older person, expectations/wishes may have already been raised that, in my opinion, should be appropriately considered.
Of course, you are practically “traumatized” by your previous heating horror, but that no longer happens in a new build in 2021, no matter what you decide.
Under this impression, one should not now go overboard on the other side and spend so much money out of “fear of repetition” on something that you can never ever save.
For us it will now be KfW40Plus AFTER ALL... but we heat with infrared + fireplace and therefore definitely need, among other things, proper photovoltaics as well as the lowest possible heat demand/good insulation. Since we also get the products we need very cheaply AND our general contractor cooperates fantastically, it fits for us again, otherwise we would never have done it. But still nothing remains, but that was never our hope. We build it this way because it fits our planned overall system, but not because KfW says so; in the priority list these things were far behind the floor plan and the proper consideration of the residents.
You can also add on in a few years, convert the attic and make room for grandma on the ground floor, etc.
I know such situations from my own life and therefore doubt this simple implementation of your idea; besides, one must be allowed and able to pay for it; that is thought too simply. Perhaps plan grandma in right away as a tenant of a small apartment.
I would already provide for that structurally or generally refuse the lady if you have not rushed too far ahead with her dreams yet.
Why not try to take the 40+ with you then? That doesn’t quite make sense to me.
People all too often carry the KfW logo on a stick before them as a saving grace.
If you wanted the measures and costs/follow-up costs for controlled residential ventilation, strong insulation (for us expensive sarking insulation), extra exterior wall insulation, different windows, slab insulation (for example, we have no underfloor heating), a photovoltaic storage system that only pays off to a limited extent, etc. anyway because it’s YOUR house, then that is ok, but if not, then you have already done and paid for some of these things because of KfW, so there is no “just take it along casually.”
What I read makes me uncertain whether with your general contractor this also works as “casually” or simply as you think, price-wise. Just be careful and have everything written down precisely, even AFTER consulting the energy advisor. General contractors sometimes just say things like that...
Just post your entire project with plan and personal circumstances then you might get completely new approaches from the forum!