I also wish houses came with an owners manual and regular check-up tooling - I'd love to have a better idea of what I'm dealing with and something to reference about what I've forgotten.

To this you add ineffective, amateurish or no repairs and maintenance and you have the perfect disaster.

It is perfectly possible to build a long lasting, maintainable, underground house, but you won't have it "cheap", expect the costs to be between 150% and 180% (if not more) of the "normal" costs for a comparable sized house built with whatever building technique is common in your area (bricks/concrete/etc.).

Mould is almost unavoidable in any (not only underground) houses with a high level of energy efficiency (in Europe those that would be classified B or A and higher, even if in my experience issues start happening at the D or C class) unless a proper (and properly calculated and maintained) mechanical ventilation system is installed.

Though you may save over the years something in heating/cooling costs, it is simply (usually) not worth it.

Don't all modern houses have a decent mechanical ventilation system? In my experience, mold is mostly an issue for older houses, which tend to have lower energy efficiency. Bad insulation does nothing to prevent mold, and if your insulation is so bad that you don't need mechanical ventilation to prevent mold, it means the wind is blowing through your house.

So just get your energy efficiency as high as possible and use proper ventilation.

No, a large number of houses (at least here EU\Italy) is not "re-built" they are (badly) adapted with increased insulation (and usually with polystirene or styrofoam "coats" - please read as waterproof insulation) and - often this is the key issue - new windows that are air tight without retrofitting "proper" mechanical ventilation systems.

And it is not uncommon to find newly built (in the last - say - 8-10 years) houses that are in energy classes C, B or A that still miss such a system or having it not providing enough air changes.

Hence I earlier said:

>unless a proper (and properly calculated and maintained) mechanical ventilation system is installed

As a matter of fact mould is usually not an issue for older houses, exactly because the walls are not completely waterproof and because of the leaks from windows and doors (that even without having wind blowing through do allow some ventilation), there may still be localized mould where thermal bridges are, but is usually a minor issue that can be solved.

Recently (again last few years) some "new generation" of "local" (as opposed to centralized) ventilation systems (basically a fan with a heat exchangers that fits in a pipe 100-160 mm for which you bore a hole in the outer walls) are becoming a needed retro-retrofit to these houses but they tend to be a little noisy (so you need timer controlled ones for bedrooms).

It really does sound like a poorly built house. I'm not an expert by any means, but flooding, seepage, pests, cracks, and mold are all extremely common basement problems. Of course, their impact on your quality of life is magnified when your whole house is effectively a basement, but it's still normal stuff.

Anyone buying a underground house, I would guess.

"When we first moved in, we ran the electric system for two weeks, nearly froze off our tail feathers, and paid double what we had been paying for natural gas heat in our previous home of 1,000 sq. ft."

Gadzooks a 2,500 sq. ft home with 14 foot domed ceilings cost double to heat then a 1,000 sq. ft home... The horror!

And I've lived in $1m+ houses and $100m+ work buildings.

There's no way you'd get me in an underground house. Except maybe in Coober Pedy.

It’s mostly the excavation, drainage, and more robust structural requirements that increase the cost of construction of an underground house to a point where it outweighs the benefits of such a house. One would want to locate any underground structure on a site that is well above the water table, and well above a flood zone - so again, the cost of locating such a plot of land increases the difficulty and expense of building such a home.

However, I think that there are advantages to residences that are - half-buried. In other words, built into a hill on a slope. The advantages to such a house would be significant if it were sited correctly with a well-engineered drainage system. For example, in the Northern hemisphere the energy savings of a house on a slope with a glass curtain wall facing south would significantly reduce heating and cooling requirements regardless of latitude. Temperatures within the structure would be pretty constant year round. In winter, when the sun recedes to the south and stays lower to the horizon, sun would shine in, and warm, the house for a major portion of the day. In the summer as the sun rises more to the East and is higher in the sky, the earth surrounding the house except for its south-facing wall would insulate the house from radiant heat, and the cooler temperature of the earth would also keep the house from warming up much.

Our summer house in New Jersey faces South, and that long side of the house is windows the entire length of the house, and about half of the surface area of that wall. In winter, on a sunny and below freezing day, the temperature inside that long room can get as high as 80 degrees F (27 C). Midday the furnace doesn’t come on at all (unless it’s a very windy day). The basement is at ground level on the south side, completely underground on the north side. The basement maintains a pretty steady temperature year-round. Had this house been built in the past 20 years rather than 60+ year ago it would have had solar panels running fans to use the basement coolness to air condition the house on the (relatively few) hot days in summer, and distribute the excess heat in winter throughout the house. As it is, it’s an extremely energy-efficient structure.