We have a additon on a crawl space and the rooms in the addition are FREEZING in winter and HOT in summer. When you access the crawl space from our full basement there is literally a breeze coming from the crawl space. I see insulation around the edges but it honestly isn't doing much - it is a whole 8 degree difference in the addition.
Do I need more insulation? Or do I have a more serious problem?
Thank you,
Kelly

Check your vents. They should be closed in the winter.

Yes, close vents and insulate between floor joists with vapor barrier toward the heated space. :)

Insulation would help but are you sure your furnace can handle that addition? I have seen many room add ons that tapped into the far end of a duct and the system just can't handle the extra space.