As I don't have one, I can't give you any good info on an HFGH, but before you site it, get with your local Soil & Water Conservation district. They will give you all the info you need on frost lines and drainage and won't charge you a penny for their genuine expertise.

As for a foundation- if you want an insulated one, prepare to dig. Actually, to give your GH both an insulated base and yourself some extra headroom, if you can live with a step up and then down at the entrance, you could put it on a short kneewall. Doing so would raise the ceiling inside and make it easier to keep it cool in summer. Heating a GH in winter is easy compared to cooling one in summer.

But to insulate the floor, you will need to excavate under and around your base, to allow room for what I found to be the easiest and most effecient material to use- Type 250 foam insulating panels.

I don't know the cost of electricity in your area but the best advice I ever received about heating my GH was to spend upfront on insulation and a highly effecient heater to save on future energy costs. It paid off big time and I realized my expected 5 year payback after only 2 winters.

Many folks are attracted to HFGF because of the relatively small cost, not realizing the additional costs/preparations especially for a year 'round setup. Depending upon what sorts of things you want to grow, what your minimum winter temps are, maximum summer temps, and desired interior temps, you might be spending quite a bit more.

Given the structural weaknesses with HFGF and necessary augmentations, I would highly recommend investigating other options. I grow orchids in a homebuilt gh in Zone 8a, and have a superior structure with benches, air chiller, etc., for ~$500.

My floor is dirt, and I understand that bricks/pavers is the best to keep clean. Gravel drains well, but is impossible to sweep up leaves, etc. Depends upon what you plan to grow.

To answer your question about placement, you need the sunniest location in your yard. If you have shade, make the priority morning sun, because this will make the biggest difference in wintertime heating. Orient your gh so that the eight-foot walls are perpendicular to the east, so that the maximum amount of morning solar energy can heat things up quickly. Of course, this will also overheat you in the summer, so you'll have to be equipped to hang shade cloth when necessary.

The orientation I've described above is the ONLY reason I've been able to grow orchids here without spending quite a bit more on heating.

There's a lot to learn, but the internet and this site are good tools for you.

-Bruce C.

"What kind of heater, BTUs i mean. I'll be using electric".

The attached link is a greenhouse heater calculator. Just estimating for your 10 X 12 in zone 6, the heating requirement for a -5 deg. outside, 50 deg inside, with twin wall polycarbonate roof, would be about about 4300 watts (19000 btu). A 220 volt greenhouse heater will supply 5600 watts, and costs about $160, not including the 220 wiring.

Here is a link that might be useful: greenhouse heater calculator

I posted this thought in another thread: what many miss about using the heater calculator is that you don't need the north wall of a gh -- especially in a northern clime. That wall can be extensively insulated, and essentially removed from the equation.

Proper orientation of the gh is extremely important to take as much advantage of the sun's rays as possible, and to have one side shaded so that the solar isn't "wasted" on an insulated wall.

-Bruce C.