I live in a house in a village in the Netherlands. The house is from 20-150 years old, depending on which section you're in.

It is cold as f in this place all winter. It's also hot as f in these new 37 degree summers.

So the question is, is the problem the old homes, or our insistence to live in inefficient buildings in places with poor climates?

Of course in this country, there's more demand for housing than can be met, so living someplace modern (efficient/comfortable) is not necessarily an option based on price. So the next choice is relocating to a different country which has a more livable climate.

I love architectural history, but we would all be better off if modern engineering and design decisions were made on new structures to replace the grossly inefficient current ones.

Currently living in a rich area, 20 stories very modern high apartment complex. The first thing I thought when stepping into the apartment for the first time with its massive windows was “jikes the windows are leaking heat like crazy”. In my old home that was 60 years old it had way better insulation (with triple layered windows).

What I’m trying to say is that this is about incentives, not about how old things are. The modern building let their tenants cover the AC cost while the old one had water heating instead included.

Not sure what part of the world you're in, but OP was describing Germany, and I'm in Netherlands. Both of these countries have pretty strict requirements for energy efficiency of new buildings. So at least here, it would be safe to assume that a < 10 year old home or apartment would be much more efficient (and comfortable) than a 30+ year old one.

Also, there's a new government initiative to provide incentives and special financing for property owners (who rent their property) to bring the efficiency of all properties up to a decent minimum level by 2030 if they wish to be allowed to continue renting them out. I imagine there may be some exclusions for certain very old properties, especially historical/monumental ones. But regardless, it should have a big positive impact.

Indeed. for example UK has the most expensive and some of the worst buildings in EU, I have seen soviet buit homes that are better than some newbuilds over here. The word of the market is 'never buy a newbuild' because you never know what they fucked up.

The stories sound like comedy: entire block of flats was built the wrong way round, someone moved into theyr flat and found the balcony was missing - the balcony door just led to a 30 meter drop. They forgot to lay cable down for internet, so a new block only has 8 megabit ADSL. The building I am in, they made the holes for fire sprinkles in the wrong place - so there is a hole in the ceiling, but nothing behind it. The sprinkler is 20 cm away from it, inside the ceiling, and if something goes wrong it won't actually be able to pop out

From what I've seen with old country side houses in France just insulating the roof and the windows can already bring very good results (heat lost through walls is usually only around 25% of all the losses). A quick and cheap solution for the roof is to lose the attic and blow the isolating material directly on it.

yeah, there are so many old houses are still sitting around in Europe. My area almost every house was built in the late 1800s. Looks pretty nice, but insulation sucks.

That estimate seems insane. Was that a “we’re too busy, go away” estimate?

How big is the house?

It is quite a standard 2-generations house (at that 1925 time), 250 m² and two apartments, + a base level with an office. I am not saying that this is the universal standard - but it is _a_ standard that I do see quite often here, especially if you look outside cities, where the turnaround for reconstructon of houses is slower.

.. and this was quite thoroughly calculated. I can tear down the house and build a new one, but apart from the waste of resources - building a new one will also cost minimum €200k - so I thought, why not 'oversize' PV, if it only costs €100k and can heat the house without improving on insulation?

To emphasize, this conclusion will likely not apply to the majority of people (especially here on HN) because as many have said here, parameters and contexts differ widely.

Does the calculation stay the same looking decades ahead?

I'd have guessed that 200k to rip it down & build a new house that has great insulation - or even to just retrofit insulation and other upgrades to the existing building - would be expected to last longer before costing the same amount against to replace (and/or pricey maintenance/insurance of the more expensive PV, aircon etc.). And might therefore work out cheaper when looked at as a 50 year question rather than 1 year one?

I don't presume to know more than you, not only don't I know about your specific situation I also know very little about these subjects generally, I'm just curious.

Yes, it is difficult and I don't think it is possible to come up with a solution that fits all. What limited I can say: Insurance for the PV is cheaper than insurance for the insulation. That is because more problems with insulation can appear (e.g. fire damage, moisture) than with PV. Insulation of old houses is also far more complex than PV (someone pointed that our here).

.. it was mentioned somewhere here, too: For some, the best solution will be to focus on reducing energy consumption; for other, the better option will be to focus on increasing local energy production. And a combination of both might be best for most.

Wow that sounds too high. Maybe insulate only the parts you frequently use, perhaps?

No offense - but insulation doesn't really work like this. If you insulate only one part, you will get massive problems with moisture through heat transfer. With insulation of old houses, so much can go wrong and then the only solution _is_ tearing down the house and building a new one.

This is very interesting. I was told by some energy expert I could isolate 3 out of 4 outer walls and it would work fine. Do you have some documentation on the “moisture through heat transfer” issue?

I do not have one at hand, but you should find this in almost any guide. It is not complicated: If you insulate 3 walls and leave one wall untouched - this wall will always be the coldest. That means the water contained in your air will condensate always at this wall (because it is the local minimum), resulting in mould and mildew on this wall over time.

Now, there are all kinds of solutions and they all have caveats. As someone said here, old houses are build so that walls are semi-permeble, meaning that heat constantly wanders to the outside. That also means that the dew point is pretty far towards the outside in winter - water can get out of the house. If you insulate the inner wall, the dew point will move more towards the inside, meaning your walls will get wet and water will take longer to move outside. If you insulate the outside, water cannot get out at all - you must find another solution to get the moisture out of the house. It gets more complicated the more you dive into this topic.

But your logic seems to indicate that only one wall will have condensation instead of 4. It’s still an improvement no?

You're concentrating 4 wall's worth of condensation onto just one wall. Instead of being spread out, all the moisture gets on the one wall.

No, that is not how condensation works, otherwise you would have automatically more condensation on the wall in a larger room. The amount of condensation on the walls is not dependent on the size of the room or the fact that it condensates on the other walls. It depends on air humidity, air temperature, wall temperature and finally, very important, wall humidity. Water will not keep on accumulating on the wall, it will reach an equilibrium at some point, when the wall itself has become moist. The fact there is condensation or not on the other walls has negligible impact on total air humidity, most of all in larger rooms. And that's the only factor out of the 4 I could imagine being impacted by condensation (or not) on the other walls.

Hence, I still do not understand the logic why isolating only a subset of walls instead of all of them would be a problem.

As I said, I had an energy efficiency specialist at my home which said that isolating 3 walls would be 75% as efficient as isolating 4 and totally recommended. So far, I have not seen any solid logic supporting the fact that isolating only 3 walls instead of 4 would *increase* the risk of mold compared to either, 4-walls all insulated, or, zero walls insulated.

The point is it won't reach an equilibrium. The outside of the house changes temperature with the day night cycle. The one uninsulated wall will be closer to the outside temperature than the other walls.

As the house cools at the end of the day the uninsulated wall will be colder than the other walls and if it's below the dew point condensation will form on it. If the temperature differential is high enough in comparison to difference in insulation between the walls then enough water will leave the air to keep the dew point below the temperature of the insulated walls and so that one wall will collect the majority of moisture (at 30C a meter cubed of saturated air carries about 30mls of water so yes condensation on a surface can heavily impact humidity). Once a wall becomes moist it will still acumulate water if it's below the dew point.

You likely will have seen real life examples of this when you look at single pane windows in otherwise insulated houses and seen them fog up/ have condensate form on them while the walls around them remain dry (if you haven't seen this but have been to houses with single pane glass in your area then condensation won't be an issue where you live).

As to your 75% efficiency point it will in fact have a lower efficiency as heat transfer increases with temperature differential. Since the room has a higher temperature differential with the outside the less insulated wall will be faster at transfering heat.

That is not to say that insulating 3 walls is a bad idea, it will almost certainly improve a rooms U value, but the worse the insulation on the remaining original wall, ceiling, and floor the less difference the 3 walls will make to the rooms U value and thus how quickly the room transfers heat.

> Do you have some documentation on the “moisture through heat transfer” issue?

Warm/er air can hold more moisture than cold/cooler air. If part of the house is warm, and you happen to cook and/or shower in it, it will have a high moisture content.

But water vapour diffuses through-out an enclosure. So that water in a gaseous phase will equally spread everywhere (eventually).

When it reaches the uninsulated part/s of the structure, the air is colder and so can't hold as much moisture leading to condensation. Get lots of condensation, and you have an environment that is suitable for mold growth (which can then release spores in the air and mess up indoor air quality (IQA)). Not to mention that water is a universal solvent, and so will turn your structure (stone, masonry, concrete, wood) to mush over time.

The place of condensation will most likely be a surface that is a large temperature change: so in the winter your inside is warm, and your uninsulated outside walls are cold.

Adding to this -- climates that have cold winters and a tradition for building well-insulated homes have detailed construction customs for how to deal with this.

Today, it's generally solved by having an airtight sheet (plastic) between the insulation and the inner wall. Sometimes placed inside the insulation. This ensures a temperature gradient that will not cause condensation inside the house.

You'll generally put a sheet that's porous but not airtight outside the insulation, to reduce heat loss due to convection and also provide an extra layer of defense against moisture damage due to wind-blown rain.

This technique necessitates good ventilation (often powered) if it's used throughout the entire house. This is to avoid saturating the inside air with humidity due to breathing and other activity, itself leading to the condensation you're trying to avoid. It can sometimes be just on e.g. floors and ceilings. Then, the rest of the structure might still be leaky enough that mostly passive ventilation will do the trick.

Older houses handle the problem by just being so leaky that condensation won't be a problem.

I still don’t get why there would be *more* moisture on the uninsulated inner wall compared to before insulating 3 out of 4 walls.

Because you add the same amount of moisture (showers, cooking, breathing), and it needs to get out before it's was evenly over all 4 walls, now only one. Your total indoor humidity is going to go up because there is less taking care of it.

That said, insulation is still the right answer, but it ain't cheap. OP should probably tear down that beautiful old house for something more modern.

Most people know that hot air rises. It's helpful to think of airflow in terms of energy (temperature is a measure of the average kinetic energy of air molecules).

Hotter air has more energy and thus will naturally "flow" towards cooler areas with less energy until equilibrium is reached.

In this example, the higher temperature air holds more moisture. That moisture will be carried along and dispersed towards the cooler wall, where it could condensate.

I do see your point, you believe the air near the uninsulated wall will have even more moisture because it’s now the only cold wall out of 4 walls. So all the moisture goes there instead of being split in 4.

But a wall will stop condensating water when reaching a certain degree of humidity. So I’m not entirely convinced one can simply divide the amount of humidity in the air by the amount of uninsulated walls (or sqm).

> I do see your point, you believe the air near the uninsulated wall will have even more moisture because it’s now the only cold wall out of 4 walls. So all the moisture goes there instead of being split in 4.

The air will not have more moisture, but rather all the moisture problems will be towards/on the uninsulated wall.

> But a wall will stop condensating water when reaching a certain degree of humidity. So I’m not entirely convinced one can simply divide the amount of humidity in the air by the amount of uninsulated walls (or sqm).

Condensation will never stop on a cold wall until all the moisture in the air is removed. If you boil a pot of water the air will fill with moisture, and the entire house will have a high humidity. But because one particular wall is cold because of a lack of insulation the condensation (water going from vapour to liquid phase) will be concentrated on that particular wall.

The condensation will continue to occur as long as you continue to add moisture to the air via cooking and bathing (hot showers, baths).

Say you have a room completely insulated except for 1 sqm. Will the entire moisture condensate on 1sqm? That could represent 1cm of water on the wall, that's physically impossible. There's a maximum amount of moisture that can condensate per unit of surface, it cannot be infinite. Where does the water go after condensating? Even if you consider it drips down and stays on the floor, the amount of water on the wall at any given time still has a maximum.

That's the bit I am missing here, it just does not add up, condensation is not something that simply keeps accumulating water on a wall if it's cold enough, there's a saturation at some point. The question is, how fast is this saturation reached? If it's fast, then isolating one out of 3 walls may not create additional moisture on the non-insulated wall.

Sorry, I hope I don't come over as being stubborn, I'm genuinely interested in insulating (I have to do it at some point), I just like to understand things and so far I do not understand why isolating 3 walls out of 4 would generate additional moisture on the remaining wall.

'That could represent 1cm of water on the wall, that's physically impossible. There's a maximum amount of moisture that can condensate per unit of surface, it cannot be infinite. '

' I do not understand why isolating 3 walls out of 4 would generate additional moisture on the remaining wall.'

you gey problems with mold way before you are anywhere near 'the physical limir of condensarion'. You dont want to be near it.

The question is not whether the amount of consensation will double or quadruple. It is weather you will have mould problems. If your wal starts getting wet, you will have mould peoblems.

Several floors were mentioned. Perhaps insulating one of them completely is an option then?

As far as I know, around 1,000 Euro / sqm is a good estimate for bringing a 200+ kWh/(sqm * a) house down to about 85-100 kWh(sqm * a)