Is the back wall where the water line comes in? If not, why do you want to walk the whole length of the greenhouse to turn on the water?

I was thinking of it being out of the way for when I don't want to do anything with the water (including a hose rolled up). But it does also come in from the back.

Regarding electric and water: I have electrical outlets on three walls of my greenhouse, and it's only 10 x 12. I use all of them, all the time. The outlet on my back wall is used for my exhaust fan mounted high in the wall, and for another table fan that I use for air circulation. In the winter, this outlet is used for one of my 1500W electric heaters that sits on the floor.

The outlet on the side wall is used for another wall-mounted fan over the front door (for air circulation also.) In the winter, I use this one for the second 1500W electric heater.

The outlet on the other side wall is close to my potting bench. I use it mostly for a radio and for a small light that stays on 24-7. (This way I can glance out a house window on a cold night and verify the power to the greenhouse is fine.)

My greenhouse is about as wide as yours and I also like a central path (mine is concrete pavers.) I water using a watering can and faucet located mid greenhouse, but if you'll be watering with a hose, I would think having it out of the way at the end of the greenhouse would be a workable solution.

My climate is zone 8a in NM, so I'm not much help on your insulation questions. Good luck!

Thanks mudhouse! Do you have 30A service going to your GH? I have 15A handy that I was going to wire in (a dedicated breaker to an outdoor outlet that I was going to move into the GH). Perhaps I'll wire an outdoor junction box to later move to 30A. I'm only planning to run one 1500W heater at most (actually not planning to run any heater, but am thinking of allowing for one). I like the idea of a constant on night-light! I know with the 1500W heater I'm cutting it close for available power on a 15A circuit, but with using minimal LED lights I should be okay. (I don't think I'll be going in there that often in the dark!) How warm do you keep your GH in the winter and what is your glazing that you need two heaters?

Thanks!

I'd have to check with my husband for the details (I should know, but we dealt with that set up 8 years ago and my memory is fuzzy.) I know we needed a separate circuit for each 1500W heater.

My greenhouse is a Harbor Freight, so only 6mm twinwall polycarbonate. I think the Riga greenhouses use at least 8mm polycarbonate (and some models, maybe 10mm?) I think there are several good greenhouse heat calculators online, but I used this one to get a rough idea of what I might need, for my greenhouse in my climate:

Greenhouse heat calculator

I don't need both 1500W heaters most of the time, but I wanted to have the capacity for the rare times I do, because I keep the GH full of plants I've spent years growing. In Feb 2011 we had crazy record lows of -6F (our normal winter lows are in the teens.) My sliding greenhouse doors froze shut for a while, and I was so happy to have two heaters in place, working on thermostats. Even with rolling blackouts for days, they managed to keep the greenhouse above freezing, and I didn't lose any plants. Phew!

My greenhouse houses my collection of cacti and succulents. Many could go lower, but to satisfy the "wimpy" kids I try to keep the gh above 42F. We used ¾” polyisocyanurate foil-faced insulation on the north wall to help with winter temps. In my climate cooling in the summer is a bigger challenge than heating in the winter.

Most of it won't apply to your (much nicer!) Riga greenhouse, but I'll post a link to the last section of my blog on our Harbor Freight, since it shows the modest thermostat set up I cobbled together.

Part Seven: Greenhouse Enhancements

Thank you. We are now planning 2 outlets for sure!

Still unsure how to insulate the north wall because of the onion shape of the greenhouse. Maybe bubble wrap, maybe something more like foam panels on the lower wall below the shelf.

So we are "excavating" around the foundation of our greenhouse to then dig down insulation (2ft deep). We are going with 2" T250 which has an R factor of 10. Since we are getting a Riga V we will then put 6 blocks down to support the "C" channel foundation frame. (1 block per corner plus an extra mid-line of the long 17.5ft wall). We will then attach the C channel to the blocks for extra anchoring just in case (theoretically this isn't needed). My question - We had planned on doing insulation horizontally and some vertically. Is it (roughly) equivalent to just double up vertically?

So if you see in the above, Option 1 (on the left) has a "C" shaped channel sitting on top of a block and then there is a pink insulation board on the inside of the greenhouse (running along the face of the block and C channel). Also you can see where I put an insulation board in-between the blocks, but under the C channel. The insulation will be cut around the location of the blocks (maybe using scrap pieces around the blocks... We'll see.)

Option 2 (on the right) only has the insulation board on the inside of the greenhouse but then also a piece going horizontally 2 ft out from the greenhouse.

We think doing Option 2 is more work. Is Option 1 sufficient? Any problems that you can foresee? Is R-20 (ie two 2" boards) overkill?

Another question - is a potting bench a must in the greenhouse? I've always potted on my driveway on a warm winter day, and had considered continuing to do this, but as I research it seems like nearly everyone has a potting bench and is something that I might want to consider? If so how large should it be? I'm assuming at least large enough to hold a couple of flats and a bag/bin of soil...

A potting bench can be as simple and handy as a little shelf at worktable height at the end of your walkway. Bags of soil can go underneath.

Horizontal floor insulation inside the greenhouse is actually counter-productive. If you are planning to grow in the winter, you want the soil under the floor to gain heat, to be released at night. The vertical side wall insulation is helpful, especially in cold climates. One, 2 in. r-20 is probably sufficient, with less positive effect with an additional one.

The horizontal insulation would be on the outside flaring out from the frame. I've heard this helps raise the frost line so that I don't have to dig quite as deep.

Each 2" is r10 so two would be r20.

I think the potting bench question is entirely personal and varies for each of us. On cold or windy days it's nice to be able to repot or fuss with plants while inside the shelter of my greenhouse. (It's really nice to have a little warm place to escape to, in the winter, and relax on my cheapo wooden stool!) But when it's really hot here I'd rather work outside on a patio.

We put a little stainless steel bar sink (thrift store find) in mine, and it is handy at times, although I don't use the sink as much as I thought I would. I have a wire shelf above the bench so I can hang hand tools, and it gives me a place to store various little things like small plastic pots, plant tags, spray bottles, twine, small stakes, scissors, etc. Below it, I have a small Rubbermaid bin where I keep my potting soil mix and a scoop. I keep soil mix components outside the GH because mine is only 10x12.

I have friends who correctly point out that a potting bench inside a smallish greenhouse takes up valuable space that could otherwise be used for plants, and they choose not to have a bench inside. I don't think it's a "must have," it just depends on how you see yourself using the space (and if you think you'd enjoy working inside.)

Szut,
Sorry I misinterpreted your drawing. Several sources recommend the outward foam board in cold climates. While there is only an incremental improvement using two vs. one insulating boards, you only want to do this once, I am sure. Here is a drawing from www.ceresgs.com :

I just don't know if the outward flaring insulation is "worth" it... Or if going down is sufficient. (The T-250 doesn't drain, so I have to watch the drainage/sloping and I want to install patio blocks on top....