Just an idea that popped in my head.

We're casually looking for a new house with some land. One of them had this detached garagelike outbuilding - it had a single-car garage door, but was much bigger overall - about 20 X 30, made entirely of masonry block.

It also has one small window on the back side and a windowless entry door.

I thought it might be useful to overwinter dormant containerized plants and keep heated only to about 32, but my questions are:

1. What kind of r-value would such a structure likely have? I'd probably stuff some insulation on the inside of the garage door as well.

2. On a sunny, warmish winter day, would the temp inside likely be higher, or lower than outdoors? My concern being if it got TOO warm plants might break dormancy in the dark while it's too cold to place them outside in the light.

3. If it would trend warmer on warm days, would a cheap ventilation system be helpful? It wouldn't need the 1 exch/min that a GH would need since it would get very little solar radiation. I'd imagine 1 exch/hr is probably enough.