Earlier quoted context omitted.
That depends on how deep you dig, but of course going deep enough has a cost that may be far greater than the kind of insulation you used. The 20-25% of increase in cost is a good proxi (from my personal experience I would have said 25-30%), but, from an economical standpoint it should be compared with savings over time (in the same region). To give you an example in Italy, last time I calculated it, this 25-30% incr…
5% return per year (or more in case of price changes or regulations forcing you to change heating source) does not seem that "philosophical".
A normal house costs - say - 200,000 "units" (dollars, euro, whatever).
Making it "energy saving" costs an additional 60,000 units.
In 20 years time you will be spending 60,000 units (3,000 per year) less for energy costs (and here we are assuming that ventilation and heating/cooling machines in the "better" house have the same maintenance costs than the ones in "normal" house, whilst usually, since they are more complex systems they tend to be more expensive).
You essentially have a "break even" point 20 years in the future, from there onwards you start saving money.
First thing, you need, now, 260,000 units instead of 200,000 (and not all people may be able to afford this).
Then, if, for whatever reasons, you don't use the house at all times in these 20 years, or you need to sell it before that time you are unlikely to fully get the savings.
Additionally, in less than 20 years time it is possible that someone comes out with a mega-para-hyper-ultra climatization device that makes yearly energy costs go down by (say) 90%.
So, if you want to do the "right thing" from a climate/energy savings point of view, by any means choose to invest in a passive house, but it remains essentially a "philosophical" decision, not an economical one.