If water damage is so bad, how come houses can be doused by rain during construction?

Mold doesn't grow IN wood. It grows in warm, damp and, importantly, dark places. Having water leak into your climate-controlled house, in between the walls or in crawl spaces is how you get mold infestations.

It's also important to note that just splashing some water on your wall will not cause mold to grow. If you soak the timber making up the frame of the house, but then you put the roof on, and the sheathing on the walls, the house dries up pretty quick, which makes it unsuitable for mold growth. As long as the spaces between the walls stays reasonably dry, even if mold spores ended up there at one time, they will die off.

To recap, in order to get mold in your house:

• Relatively warm
• Regularly damp
• Reasonably dark