Most likely not required, you still need chill hours, but if you really wanted a specific apple that was not hardy to your area getting it on a very dwarfing root stock ( requires staking) could fit in a garden shed size greenhouse.

I am experimenting with that right now with a few pears and an apple. My reasoning, we live in Sask. and in my greenhouse I currently grow some zone 5 seedless table grapes with no problems. Yet!

The greenhouse is 16' x20' double walled with roll up sides and is inflated. It is heated with our outside boiler and we start it up March 1st and close it down Nov 30th, give or take. So It gets very cold in the winter but I keep 2 ft of straw mulch in there and I think the fact that the sun, even on the coldest days, warms it up a little changes it's zone rating. But I am not a fruit expert, and I am doing this for fun.

I am doing the pears and apples as "stepovers", which are a low growing espalier with two single arms that will stretch along each of the three 16' beds. These will not get copious amounts of fruit but hey, that is not my objective. My objective is to get a variety that I cannot get anywhere else. My trees were just grafted last year so it will be many years before I see any results, the apple will, of course, fruit way before the pears.

My plums are fan espaliered on the back wall because it is covered with plywood and styro insulation. Again, the trees are small so no results yet.

Very cool, urbo. I would love to see pictures sometime

Really cool. That's what I was thinking. There are a lot of things I would like to grow, but my season is like 3-4 weeks too short (it's really too short to grow anything normally, and probably not hot enough, either). I've been inspired to build a greenhouse

One thing I have noticed about greenhouses is that heat build up in the summer is harder to manage than cool temps. My greenhouse has sides that roll up about 4 feet, this creates a wonderful cross breeze and still my exhaust fan runs constantly. I find that I also need to keep the door open and a standing fan operating or the resulting heat cooks the plants.