Here's the biggest challenge in year-round growing - any clear material that makes a good greenhouse also makes very poor insulation. They measure insulation in "r-value." A typical new house has r12 walls. The most expensive greenhouse covering is double-wall glass, and that is about r2. Plastic will be an even lower value. You can build a very pretty lean-to greenhouse out of polycarbonate and it will work great on a sunny day, but your heat will have to run constantly on a cold winter night to keep up with the heat loss. When your utility bill comes, you will probably have spent more in electricity than you produced in food.

The best design for a true year-round lean-to for you would have a lot of insulation, and not a lot of clear wall or roof space. I would want some sort of insulated cover, like a hot tub cover, that you can put over the clear roof on a cold night, and then open in the morning. It would pay for itself very quickly.

Another alternative is to just not use the greenhouse all year. If you have the space, it's not that hard to grow greens indoors under artificial light. It does cost money to run lights, but it's a lot more efficient than trying to heat a poorly insulated space.

I hope I didn't discourage you too much. Good luck with it, and I wish you the best of health!

Hmmmmmm........ does anybody successfully have a year-round greenhouse?? Should I be looking into something other than a lean-to? Or would that be more expensive to heat??

I wish I had the space indoors. There HAS to be a solution to this. I am sure somebody has figured it out!