Mold is caused by not handing water vapor well, you can have a building that is not climate controlled that has no issues with mold. In fact, mold is usually caused by preventing the free-flow of water vapor while conditioning the house.

https://www.youtube.com/watch?v=IEMZk5Kjqkw

Freezing pipes is another issue, but that can be remedied by conditioning to 40 or 50 degrees (freedom degrees™) but I suppose you could build a building with anti-freeze dedicated to the piping itself.

Ventilation controls the mold in places you can see, like showers, but has little effect on mold growth in concealed places like sealed wall cavities. That's the far more dangerous form of mold, because you can't clean it.

Many old uninsulated wood houses, despite their reputations for being preserved primarily due to their mold resistant old growth structural lumber, were preserved in major part by the fact that they were constantly being heated all winter by high capacity heating equipment like wood or coal stoves that had to put out a ton of heat (at very low efficiency) to overcome the lack of heat distribution, resulting in significant vapor drive [1] wherein radiant heat and air pressure pushes water vapor out of warm spaces through permeable walls, therefore keeping them dry.

Vapor drive and the location of the dewpoint boundary are important principles in designing a house's envelope, and maintaining permanently enclosed mold sensitive materials above the dewpoint is needed to prevent mold in walls and other areas.

This is especially critical in houses with vapor barriers (usually plastic film in the wall), which essentially trap vapor on either side of the barrier, so the dewpoint boundary (the line in the wall assembly maintained at a temperature where vapor condenses) should always be in a place that can easily dry out the condensate that develops there. Otherwise, mold will likely grow.

1. https://www.finehomebuilding.com/project-guides/insulation/v...

That's the main point - much of the mold problem can be attributed to vapor barriers; if you have them, you have to maintain the thermal envelope and the moisture content; if you do not have them, you only really have to worry about it in perpetually wet areas (bathrooms, kitchens) as the others will let the air and vapor through.

This is why abandoned houses often don't have much mold to speak of unless you're in a very year-round damp climate.

So if we wanted to build mold-resistant houses that were designed to idle at 50 or 60 degrees, we certainly could.

Most houses should probably have more humidifiers/dehumidifiers than they do; much of what we do for "climate control" is very ancient technology.

> That's the main point - much of the mold problem can be attributed to vapor barriers;

Indeed, if I lived in a cold climate, I'd much rather have a vapor permeable but continuously sealed and insulated wall assembly than a vapor barrier.

> So if we wanted to build mold-resistant houses that were designed to idle at 50 or 60 degrees, we certainly could

Totally. Wood framing, plywood sheathing, and drywall's paper backing are prone to mold when exposed to condensation, but those are the most economical materials we have for building. Keeping condensation off those materials at low temps is challenging, and most easily accomplished by heating them along with the space.

OTOH concrete (i.e ICF) is pretty impervious to condensation, although it has other major issues with that make it not ideal for most house walls.

> much of what we do for "climate control" is very ancient technology

Totally++

At least codes are starting to get better - requiring results rather than methods.

I've used a cheap hygrometer last winter, during which the air inside my home was always way too dry. I had to place humidifiers (with some success). The difference in humidity for inside and outside temperatures is huge. You can calculate the relative humidity for different temperatures with online calculators such as [0].

Long story short; if you still heat your home, but some degrees lower than you used to do, you are probably fine regarding mould.

[0] https://www.omnicalculator.com/physics/relative-humidity

I don't think the article means to suggest that you let your house go completely to the elements - only that you maintain a lower more economical temperature. How is mold going to grow more at 55F than it would at 70F? As long as you ventilate moisture and minimize condensation you can keep the mold under control.

Yeah, many people don't realize that the importance of climate control is more so for moisture than temperature. Although winter is "dry" it's wild how much ambient moisture humans emit - anyone who's grown any kind of mushroom can also attest to how acutely fungus react to even minute (5-10f) fluctuations in temperature. If you have a compost pile, wait for the first time in fall where soil temps dip below 70F or if you have a light freeze - you'll likely see the entirety of your compost pile fruiting with mushrooms :)

No it does not. You have to control the humidity, not the temperature.

As @bombcar pointed out, preventing airflow to retain heat can cause mold.

I've lived in two houses and many flats and never had any mold issue. Is it only an old house problem ?

Mold is extremely variant in where it shows up due to

* climate (ambient humidity and temperature)

* ventilation (both HVAC systems and habits of leaving windows open etc., but also draftiness in older houses)

I'd say it's primarily a humidity (or specifically walls-at-dew-point) problem, but that is of course highly inter-twined with temperature.

Old houses can be more affected due to the addition of inappropriate modern materials, or for example lacking a bathroom extractor fan.

Not to mention freezing pipes.

That's not really the discussion. It is so much cheaper and easier to heat a house above freezing temps than to heat it to human-comfortable temps.

That's an airflow issue, not a heat issue.

Heat both helps with airflow and reduces the need of it.

How do you cheaply create airflow in winter? Open windows 24/7 and turn on a fan? Thus increasing the need for body-heating and reducing house temperature even further?