What causes mould in new-builds?

If you house found mould in your new build house, this article is for you. We will discuss the principal reasons why mould is appearing and what you can do about it depending on where it is happening....

Mould inside cupboards / wardrobes:
Materials in new builds such as plaster and timber (skirting boards etc) need time and ventilation to dry out. It is particularly common to find mould on skirting boards inside cupboards under the stairs and areas that lack ventilation such as kitchen cupboards and in wardrobes. This is due to a combination of ventilation and the materials drying out.
What to do: Contrary to popular belief, bleach can’t kill mould on porous surfaces, e.g wood, because mould spreads its roots deep into porous surfaces. Even after applying bleach and wiping away from these surfaces, the mould will continue to grow beneath the surface and will return to the area you cleaned in a short amount of time. Instead, try damping a cloth with white wine vinegar and leave the cupboard adjar for a couple of weeks.

Mould up the walls:
We do not want to rule out the possibility of skirting boards (on the ground floor at the external walls) being damp caused by moisture externally getting into the cavity and bridging or likewise from a leak from a pipe... However this is very unlikely and only to be considered when the house has gone through the drying out period (timescale is somewhat weather-dependent) or there are other signs such as wet patches rather than just mould.
So, to put your mind at rest if you have mould in your new-build house, it is incredibly unlikely to be associated with the major concerns you may be concerned about such as rising damp or a leak.
The picture shown here of mould on the wall looks like it is a serious issue (in the sense of it being possibly moisture coming from the outside walls to the inside) but it is actually just the wet dot and dab adhesive that is bridging moisture through as it hasn't properly dried out.

Mould tends to be attracted to the area getting the least ventilation, which is why it is common to find it in corners when you move furniture out the way, or sometimes you may get it around windows.
Sometimes we visit houses where the occupants have been drying their clothes on the radiators and this has created excess moisture in the air (known as Interstitial condensation) which often combines with it being during winter months where the trickle vents have been closed. A sign of Interstitial condensation is when we see mould in areas we wouldn't typically expect to see it such as around radiators (as per the comment that mould is attracted to the colder part of the room) which means the cause is excess moisture and lack of ventilation. 
What to do: ensure that you do not have furniture up against the walls and open trickle vents in your house to ensure adequate air flow is circulating.
Do not dry clothes inside the home which is creating excess moisture in the air.

Mould in the loft 
If the moisture content of timbers reach 18-20% content, the timbers will show signs with green or black mould. This is only on untreated (non marine grade) timbers. This is typically (not always) caused by a lack of ventilation or gaps in the insulation .... and often the worse examples are a combination of the two.
What to do: This is typically a job for your developer who will want to check for adequate ventilation through the eaves and ridge, and check for gaps in insulation. 

We hope this article has been useful if you are experiencing mould in your new build. Please consider a new build snagging survey if you have concerns.