How should I prevent the newly constructed house from molding?

[Oldboy]

There is no reason to do anything about this. It will dry out by spring. When the house is finished, it will remain dry and not cause any problems. Since the interior of the house is covered in plastic, no mold spores will enter the house regardless of how much mold there might be in the frame. What's visible in the pictures now is nothing to worry about.

If the house is insulated, etc., during the winter, it is a problem because thick insulation and plastic on the inside will take a looooong time to dry out. That is, it will worsen the situation.

 

[Cheesen]

Building a new 1.5-story house. We are very afraid of mold and growth on the wood. Therefore, we quickly proceeded with the framework during late summer, with help from carpenters. This went quickly and it hardly rained on the structure before the roof was on and the membrane around the house. When I measured the moisture content of the frame, it was around 11-13%. This made me very happy and I thought we had done well.

Autumn came and the window delivery got delayed, which prolonged the installation of cladding and windows. The exterior of the house was completed about 3 weeks ago, so we didn't manage to insulate and heat the house before winter.

Now to the big concerns, we live on the west coast and for the past month, it has rained almost constantly and been around 5-10 degrees with extremely high humidity. This seems to have caused the frame to absorb moisture from the air? I can't understand what else has happened because now the moisture content of the frame is around 16-18% and mold has started forming all over inside the house. This makes both me and my wife stressed and depressed.

What can we do now? Should I just live with it and wait until spring for the house to dry? Should I start sanding/planing away the mold? It's a bit difficult to heat the house since it's not insulated and the entire floor is open down to the crawl space. Will a dehumidifier help in this situation when it is so open?

These are a few examples of how it looks now, there are similar growths in about ~20 other places, and it seems to be increasing every day.

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If you have a slab foundation, it's the foundation drying out. It's important to make the house airtight and warm as soon as possible to avoid moisture in the frame. You don't need to worry, the frame will dry over time, but you won't escape cosmetic blemishes that you'll never see.

 

[Tysta musen]

Make sure to maintain an even and good temperature. It always pays off. Mold comes from moisture, and moisture arises when it is enclosed and not heated. Look at all the unheated houses that deteriorate quite quickly but previously functioned well when they were heated.
Maintain good ventilation, but ensure you never leave spaces unheated under the impression that it will save costs—it can turn out to be the opposite! Mold is a living organism and thrives where moisture exists and where moisture remains because spaces are unheated and nothing dries out.
It's better to keep the house warm—skip dehumidifiers as these consume electricity and only work locally where they are placed.