Cold room in my basement - My idea

[Snyper708]

The question was about "why", not about "when".

[Applejack]

Crawl spaces are vented to keep condensation from forming. That is one reason to put a plastic barrier under the crawl space or basement. If hot air gets under there it will rise into house making your house feel hotter. Same in winter if your vents are left open it will bring in cold air to rise up into house as well making house feel colder.. The barrier will help to keep the moister from rising from the ground and causing mold and rot. You need to know when to open the vents and when to close them.. Hope this helps.