[kitd]

It is interesting that you insulate under the house.

One of the more intriguing passive house designs I saw was one where the insulation went down 2-3m into the ground all around the house footprint. This trapped the natural ground heat within that area and fed it upwards into the house. It took about 18 months for the ground to warm up, but once it was there, the ground/house warmed itself with virtually no input.

This was in the UK. Colder climates may vary ofc.

[mrweasel]

> It is interesting that you insulate under the house.

Isn't that pretty normal, I mean maybe not three meters down, but modern foundations are required to be isolated in many places. The legal requirement in Denmark is at least 300mm of isolation under the house.

[8fingerlouie]

And that's not a new thing either.

In my 1970's house we have 150mm insulation under the house from the original build, 150mm in the walls and 200mm on the roof.

We added another part to the house a few years ago, and that was 300mm insulation in floor/walls/roof. Since the walls are made of brick with a depth of 7cm, it means the walls are 7+7+30= 44cm thick (plus some "slack")

Even my 1980's summerhouse has 100mm insulation in floor/walls/roof.

[jmrm]

That depends of the the place where you live. In middle to the south of Spain, the floor of houses are normally made of marble (or other ceramic material) slabs on top of a little layer of some glue cement, on top of the armoured concrete slab foundation, but on the north is a lot common to have wooden floors with air chamber of a similar size.

[kitd]

It is indeed normal. I mentioned it by way of an intro to the unusual alternative I saw.

[poseva]

Really interesting. I've read about also "foundation insulation skirt" that allows you to create a warmer earth mass under the house.

To be honest this was the biggest "complaint" that others had in regards of how a built the house, the general knowledge says that the earth is warm and you don't need to insulate against it... but the earth is maybe 5-10 degree, of course warmer than outside -5..-10 but still a lot colder than what we want inside the house, 20,21 degree C.

[jaclaz]

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% increase of costs corresponds - loosely - to the costs of heating for 20 years or so (bar the crazy increases in prices of energy that just happened), so it becomes more a "philosophical" choice than anything else to go for passive or almost passive.

[Sankozi]

5% return per year (or more in case of price changes or regulations forcing you to change heating source) does not seem that "philosophical".

[jaclaz]

I don't understand fully your way of reasoning.

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.

[maxerickson]

If you step back a bit, it makes sense for society to push for the construction techniques that minimize the lifetime cost of the building. Here, buildings typically last for much longer than 20 years.

And then there's the whole thing where energy costs may not be fully priced into the use.

[jaclaz]

Sure, but then that is a "political" decision at government level, not your "free" choice.

It is clear that the (good) trend is towards mandating "better" insulation (and thus less energy consumption) but it is not like a government can say "ok, starting tomorrow all new houses must be passive", as that translates to "ok, starting from tomorrow price of all new houses will increase by 30%".

They are introducing - little by little - minimal requirements, and introducing in parallel some (BTW badly implemented at least here in Italy) economic incentives to better existing houses but it will take many years before they can impose "only passive" houses, and in any case, "new houses" are such a trifling percentage of existing buildings that they won't make a dent in the overall energy consumption, it is much more effective, given the amount to slightly better the much larger amount of existing buildings.

Also it is not as easy as it seems, for the last 10-20 years a number of houses have been built in the (at the time) energy classes A-B-C without mechanical ventilation/heat exchangers, with - let's call them "not fully tested" - construction methods and now that they are aging they show the problems emerging (humidity/mould, maintenance of windows, decay of insulation packets/facades, etc.), as often happens with new technologies.

[beerandt]

>construction techniques that minimize the lifetime cost of the building. Here, buildings typically last for much longer than 20 years. And then there's the whole thing where energy costs may not be fully priced into the use.

It goes both ways. Investing in capex has to be balanced against potential capex and opex market changes, not just today's market.

Unless that 0% rate gets passed onto you, there's a fairly rigid payback wall at 30 yrs where no amount of investment is going to make financial sense. (It's why despite loan terms growing for everything else, mortgages are still capped at 30 yrs.

What happens when the market is flooded with cheap renewable electricity, as is promised? Suddenly your payback period is extended beyond what makes sense.

Or advances in technology result in a cheaper, better insulation material?

And then there's the potential external costs of not just energy, but material and construction. It wasn't that long ago that asbestos singles covered nearly every new house because of its fire resistance and insulating properties.

The cost there also seemed to pay for itself, until we discovered the true cost of asbestos mitigation and removal.

[ClumsyPilot]

"You essentially have a "break even" point 20 years in the future, from there onwards you start saving money."

That's exactly how a 5% roi investment works. There is nothing unusual here.

"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%"

And it's possible second coming of Christ will happen, or an asteroid will fall, and you'd be better off soending money on hookers and cocaine.

A plan that relies on some unrelated events to solve your problems is not a plan. Why bother planning at all then?

[jaclaz]

>That's exactly how a 5% roi investment works.

Not exactly, in a 20 years 5% roi investment you normally get your invested capital (admittedly reduced in real terms by inflation) back.

In this case a the end of the 20 years you have something that has degraded and that probably needs replacing (talking of ventilation systems or solar panels) and/or needs repairs.

I find it more like a 5 year lease for a car vs buying it cash.

[renewiltord]

This was a problem that hit the first solar adopters. Their break-even was so far in the future because the technology really ramped up later. Of course, one could argue perhaps that wouldn't have happened without the adoption. And perhaps argue against that again that it was gov subsidies that really pushed solar to primetime.

[empiricus]

Not only "philosophical", better insulated houses are also more comfortable.

[jaclaz]

Sure, but not all houses are built for "you" to live in perpetually.

You build a house according to the minimal requirements of your local codes/norms.

If you next year go to another city you may either sell the house or rent it (at average market value).

You build a "passive house".

If you next year go to another city you may either sell the house or rent it.

Do you believe you can easily get 30% more rent or sale price because it is passive?

[baq]

did you include heating costs rate of change growing? (i.e. prices rise more % yoy with each year?)

[tejohnso]

Insulation under the home, and skirted around it. You may be thinking of a Frost Protected Shallow Foundation[1]. A nice alternative to excavating in order to get below the frost line. I dream of doing this as part of a self built small passive house project.

[1]: https://www.greenbuildingsolutions.org/blog/frost-protected-...

[swader999]

ICF construction where the foundation form is Styrofoam Lego like blocks that concrete is poured into achieves this shallow and in full basement hooded. A lot more homes in Canada use this approach now.

[leobg]

Exactly. Talking about thermal mass!

There’s also the movement of underground houses. They use the ground for cooling in summer and for insulation in winter. Also it apparently makes for great noise reduction, in spite of having lots of windows, light and views.

See the book “Recovering America: A More Gentle Way to Build”.

[swader999]

Underground houses can be a nightmare dealing with water infiltration, codes and the power of soil.

[alksjdalkj]

> It is interesting that you insulate under the house.

I think anyone who's gone camping will appreciate the need for insulation between the ground and whatever you're trying to keep warm - a good sleeping pad is crucial for keeping warm.

[markvdb]

> It is interesting that you insulate under the house.

Near our place in the countryside, required foundation depth is 1.4m to protect from frost heave. Use an insulated slab and that requirement goes away. The insulation keeps the heat in the ground. It protects the ground under the house from freezing.

Nobody cares about regulations here, but they do about getting proper foundations...

[lelanthran]

> The insulation keeps the heat in the ground. It protects the ground under the house from freezing.

If it is preventing the ground under the house from freezing, then it is supplying heat to that ground. That's a energy-negative process - some of the heat you generate is used to maintain the warmth of the ground.

[markvdb]

Au contraire, my dear Watson.

Without under-slab insulation, the heat emanating from the ground below the house escapes very quickly. This heat we don't generate. It occurs naturally. This is about using the naturally escaping heat to keep the ground under the house from freezing, about raising the frost depth.

This technique is especially interesting for holiday homes not permanently heated in northern climates. It's fairly standard in Scandinavia, up and coming in the Baltics, but less known in the US.

In the US, it's usually called FPFS or frost protected shallow foundations. [0]

[0] https://www.ncei.noaa.gov/products/land-based-station/frost-...

[jounker]

Some of your heat is always going into the ground. The insulation prevents it from dissipating into the environment.

[throw0101a]

> It is interesting that you insulate under the house.

This is part of the building code in many areas: do a search for [under] "slab insulation".

* https://www.buildingscience.com/documents/information-sheets...

* https://www.finehomebuilding.com/project-guides/insulation/i...

It should be at least R-10 (RSI 1.8):

* https://www.youtube.com/watch?v=O2dNp9bicSk

* https://www.youtube.com/watch?v=XKp0wRzvR-g

[Gravityloss]

How would that work? Average temperature in the UK is about 15 C. If your house is at 24 C, this would mean you are constantly leaking heat into the ground from the bottom...

I guess one can consider the cube of earth an insulator, it's got a lousy insulation value per meter but it makes it up in thickness.

[arethuza]

Don't think 15C is correct - looks more like 8.5C to 11C in England and 7C to 9C in Scotland.

http://projectbritain.com/weather/average.htm

[a_square_peg]

You can look up ground temperature for your location here - https://weatherdownloader.oikolab.com/downloader.

Layer 4 is between 1m to 3m depth beneath the surface.

[arethuza]

Apologies, I didn't appreciate you meant average temperature underground - that is definitely much warmer. We have a ventilation shaft for an old limestone mine near our house and on a cold day the warm air rising from it is very noticeable.

[a_square_peg]

I wasn't the commenter so no worries about apologies... just wanted to point out where you can find this information. :)

[Gravityloss]

Sorry, I was wrong indeed, thanks for the correction

[whirlwin]

We have an old house from 1988 located in Norway. Walking on the non-insulated wooden floor is very unpleasant. We will refurbish, and insulate under the floor, but it will not be anything near a passive house because of other construction shortcomings

[ricardobayes]

well try non-insulated tiles here in Spain haha. I don't know why houses are built to such a low standard in Spain. Even the UK had better quality constructions when I was there, and that says a lot (single glazed windows, poor insulation, weak plumbing)

[madaxe_again]

Portugal manage to be even worse. You’ll be stood there in someone’s kitchen wearing a coat and gloves, watching your breath condense, and they’ll be like “oh but we don’t get cold winters like you do in the northern countries”. That’s the rationale. The reason is actually more likely financial.

[joking]

no harsh climate overall so much less insulation is needed?

[ricardobayes]

Mainland Spain falls into the single digits at night at winter so definitely would need insulation, because there is also no central heating. People resort to heating with their aircons and portable heaters. I'm sad because I expected better infrastructure from 45% income tax at the highest bracket.

[jakub_g]

I come from Poland (sub-zero in winter; can be anywhere from -20C to +10C but typically 0-5C), but the winter I lived on the Spanish eastern coast was the coldest in my life: thin walls and windows, stone floor, no heating apart from little portable heaters, 5 degrees and rain outside.

Now I live in French southern coast, the buildings are slightly better but still poor. In my place even with all heaters I have on max, I'm nowhere near as comfortable as in properly built and heated apartments in my home place (actually when visiting friends in Poland in winter I'm almost overheating!).

Basically half of the year it's quite uncomfortable to stay at home for prolonged time: for ~4 months a year at winter; then again for ~2-3 months at summer (+26C at home with blinds down unless you put aircon on max for hours). Kinda suboptimal for WFH to be honest :)

[inglor_cz]

I have an acquaintance in Madrid. Visiting her, I never know what to prepare for.

An Easter visit was miserable, because the condo building did not even have central heating. With night temperatures around 5 degree Celsius, I could barely sleep.

Then comes the summer and 40+ Celsius is at least as unbearable...

Spanish construction standards are pretty ascetic.

[voisin]

Do you have a link on this? I’d love to read more about this.