Most houses have effective heating systems that are used most of the time, except summer. Keeping the temperature above 18 degrees, centigrade pretty much stops damp and mold
Most buildings are double skin construction - this creates better insulation and reduces condensation as the inner wall is warm. This is usually paired with double glazing.
Bathrooms and shower rooms should have an extractor fan (usually triggered by moisture or by the light is on), which pulls moist air out. Many people have them above the cooker too.
Most windows have ‘trickle vents’ that ensure a level of airflow.
There are exceptions, of course. Some WW2 era buildings were built with single skins, and are prone to condensation. Some older building uses single glazing and can be hard to heat, and some people cannot afford to keep all their homes warm (or have inadequate heating), so end up with mold forming in the cold rooms.
Some flats are built with poor ventilation. Some people deliberately block ventilation to reduce heating costs, which causes damp.
There is also the possibility of roof damage, such as leaking joints, which is a wet climate that can cause much damage.
If your house is moldy, the chances are it’s down to condensation and not understanding its causes, or not being bothered to care. My home is a 1960s self-build, extended in 2004. It’s double-glazed throughout and centrally heated. The air inside is not “wet.” In fact, in winter, the relative humidity indoors is usually lower than in summer as the outside air, being more relaxed, can hold less water. When it’s heated, the RH drops. See the difference between in and out last night. 61% is perfectly fine indoors.
If you’re going to add water to the air in the house continually, you need to ventilate it. Every time you use the gas stove or oven, it adds water to the atmosphere. Use a ventilated or condensing dryer or hang your clothes outside to dry rather than indoors. Contrary to popular belief, you can dry your clothes outside in winter in the UK, even if it’s cold. Okay, you have to keep an eye on the weather, but it lowers your bills.
Condensation can become trapped on the inside of an outside wall if you’re not careful, and cause mold. We used to have our coats hanging up against an outer wall. The jackets leaning against the wall acted as a layer of thermal insulation, keeping it cold. One day I discovered the wall damp and moldy. Although the coats stopped the wall getting warm, air could still get through slowly, and the moisture condensed out in winter onto the cold wall. The reduced movement of wind did not allow the moisture to evaporate, hence the mold. The answer was to move the coats away from the wall. Problem solved. My wife thought it was rain ingress (through a cavity wall), but it wasn’t.
Having said all that, I’ve seen some shocking low-end rental properties with awful mold and damp, but that was down to poor maintenance, being semi-derelict or being left for months on end with no heating and all the windows shut. If you trap humid summer air in a house and leave it there all winter with no heat and ventilation, you’re going to get problems.
1 in 5 houses in the UK suffer from mold, and it affects both old and new builds, the latest builds being better insulated. The problem is cultural - like not rinsing washing up liquid off crockery - and due to lack of ventilation i.e., not opening windows at least for an hour a day. Indeed I remember in the house I grew up in, many window frames were painted shut!
In Germany and many other colder countries it is quite normal and routine to open the windows to air the house at least twice a day for at least half an hour, even with minus temperatures outside (which are uncommon in most parts of the UK) and most people in places like Austria or Romania always sleep with the window a little bit open, even when it is 20 degrees below zero outside.
Having returned to the UK from living overseas, I had seen my flatmate's rooms - which were beautiful and mold-free when they moved in last year - become moldy while my room remains mold-free. The reason is that these flatmates have had their windows closed since August so no surprise really, while I always have one window open at least a couple of centimeters, which is no problem as it hasn’t even dropped below zero in London this winter. Of course, it is the landlord’s fault, in any case.
Both houses & the weather vary in the UK.
Generally, older houses may be more prone to damp for a number of reasons:
Solid single skin brickwork is more prone to damp ingress than double skin with the cavity. Bricks are porous.
Damp-proof courses & seals around windows & doors are more likely to fail in older houses.
Less efficient windows & doors that are poor insulators & may have rotted.
Lack of built-in ventilation. Older houses relied on the fireplace - chimneys to draw in air. Often these have been blocked in overtime.
Long-standing leaks. Gutters, downpipes & wall, buried water pipes that have not been maintained.
Mould usually occurs in older, poorly maintained houses. Where mold occurs in modern homes, it is often caused by human habit: pans boiling away for hours in kitchens with windows closed tight.
The exception is the aptly named dry rot, which is a fungus that spreads by airborne spoors.
Weather-wise there are 2 generalizations that can be made about our weather:
The South is usually warmer than the North.
The East is usually drier than the West.
We have a house in the UK and one in South Carolina, so I feel I can provide a balanced answer to this question.
In general, houses in South Carolina (and the other Southern States) are more likely to suffer mold due to the high humidity, which is not something we suffer from in the UK.
If there is a mold problem in the UK, it is most likely to apply to an older house where the damp course is no longer active and has not been appropriately maintained. Reasonably excusable in a, for example, four-hundred-year-old house. By contrast, we have seen many, many cases of houses less than twenty years old with serious mold problems in South Carolina, often leading to expensive lawsuits.
So, yet another silly question with little or no validity on Quora. It seems to be a recurring theme these days.
Look, this sounds quite rude the way you asked this. However, I will answer, the new build houses are not moldy as they were designed for modern central heating, the older homes and I are talking over say 60 years and older were not designed for central heating and usually had a 9-inch brick wall ie, two courses of brick with no gap for insulation. So when these properties are modernized with modern central heating, and during the colder months, the heat generated hits these cold brick walls resulting in condensation and mold, drying clothes on the radiators add to this problem.