Hi. I'd really appreciate some help on the next steps for my greenhouse. The foundation (see photo) is 14x22' and it's located at 4100' in NE Oregon, Zone 5a. The front of the foundation faces directly south. It, and most of the east & west sides are apx. 2' below grade and back wall is about 5' below. Before backfilling I plan on installing a French drain along the exterior. Any thoughts on rigid PVC vs the flex drain pipe? Do you recommend using some kind of coating on the foundation before backfilling?

For the floor I'm thinking of adding a few inches of gravel, then a top layer of bricks, maybe with a bit of sand to hold them, for any areas that aren't raised beds. Will try to get the height of the bricks to be just above footer height. How's that sound?

I plan on using stick construction with 3x6' double pane windows horizontally on the S. side, which should give a little over 6' of interior headspace on the low (south) side. Will also use some windows on the east & west sides.

Planning on a shed roof and using multi-layer polycarbonate. What pitch would you recommended for a fairly snowy climate at about 45º latitude? And do you think it'd be good to extend the roof beyond the south wall by a foot or two to avoid rain and snow running down the south wall? Would you recommend double or triple layer polycarb and do know of any good sources for long sheets?

What do you recommend for ventilation. Summer temps are often in the 80's and sometimes 90's here. And what about winter - would it be good to include a fan to circulate air even if the outdoor vents are sealed up?

Hoping to at least overwinter some greens. Planning on including a small Cadet-type wall heater to protect against the coldest weather. (Only have 110 wired to the greenhouse so probably can't put in a stronger heater.) And if having the greenhouse partially in the earth is enough to keep the temperatures moderate in the winter I hope to be able to grow a citrus tree.

Would really welcome your thoughts and suggestions on any of the above. Thanks!

Hi @leon6 and

Nice foundation. I think the flex should be fine. PVC if you like overkill.

Are you going to insulate the outside of the foundation before you grade around the greenhouse? (2-4" hard pink insulation board). If not, I would consider using a basement sealing paint on the inside of the wall or (much better) something like BlackJack 57 rubberized coating on the outside to prevent moisture infiltration.

I like your floor: gravel, paver leveling sand, concrete bricks and sand brushed into the cracks is what I did, although I would have really liked to have installed a ground to air heat exchanger. They run a good price, and I could not dig down that far, but it makes a difference in heating and cooling. Wish I knew what growing zone you are in (Plant Hardiness Zone). There's place in your profile to put it so others know. If you don't know your growing zone, check here: https://garden.org/nga/zipzone...

Check out the double pane windows to see UV rating. Also, clear windows can easily burn plants in a greenhouse. You'll have to plan for shade cloth. Triple pane polycarbonate diffuses the light better and is strong. Depending on the windows you were planning to buy, it may also be cheaper. You could incorporate them into your stick construction. They come in all sizes and can be cut with a variety of saws.

Roof. Yes, 45 degrees if a lot of snow in your area or a roof rake with something soft to cover the metal so it doesn't scratch the polycarb. Once again, I like triple polycarb. Greenhouse Megastore at https://www.greenhousemegastor... has polycarb sheets. I have used GHMS for many purchases. They are reliable and I have found their customer service good. Shop around though for better pricing/shipping before you purchase.

My greenhouse is 14 x 20, so it is a similar size. (Riga XL6 distributed in the US by Exaco: https://www.exaco.com/greenhou...) I have a fan inside that circulates the air 24/7. Nothing fancy, just one of those floor drying fans on a table at one end. https://www.google.com/search?...

I also have the following set on a thermostat. 24" automatic intake louvre and a 20"exhaust fan. I can change the complete volume of air in less than a minute. Bought all three through a J&D distributor. Once again, shop around. Prices can vary a lot. J&D makes quality equipment. There are other good companies for this equipment as well.
FAN: https://jdmfg.com/product/indo...
Shutter: https://jdmfg.com/product/alum...
Thermostat Controller: https://jdmfg.com/product/vc11...

Winter growing. I am in Zone 6b. I use an oil-filled radiator type heater on the coldest nights to stay around 40 degrees. I was fine this first winter in my new greenhouse even at temps down to 8 degrees. I also have a 425-gallon pond in my gh for a heat sink, the brick floor that absorbs heat, and Phase Chage Material Panels that store heat and release it during the night. Once again, it depends on your zone what you will need.

Look forward to hearing about your progress. Ask more questions. There are a lot of knowledgeable greenhouse growers on this forum. Some check in daily; some less often. And remember, we love pictures!

Jim

Thanks so much Jim - that's really helpful. Have some follow up questions for you but for now just wanted to say a quick thank you and let you know that I'm in Zone 5.

Whoops - that's 5a.

leon6 said: Whoops - that's 5a.

Don't know if you use a PC (old-timer like me), laptop, tablet or phone, but look for your profile and you can add your name, Zone, your area (specific or general). When you ask a question, members will then see that (like you see in this post in the upper right corner). It helps others to better understand your growing needs, and they can give more specific advice. I kind of figured you had a cold winter in your area after seeing that great foundation. They don't build them like that in milder climates. Talk again!

Thanks. Just updated my profile.

Hi Jim.

I'd prefer to use a coating on the exterior instead of insulation board. Your recommendation of BlackJack57 sounds good. Any idea how it compares to Apocalypse 301 or Henry Asphalt Emulsion?

Hadn't seen those fans you mentioned. How do you think that would compare to wiring one or two fans in the ceiling?

Sounds like your ventilation works really well. Had thought about getting two fans and installing them facing opposite directions so that one would act as an intake and the other as exhaust. What do you think the pros & cons are of doing that compared to your system with one intake shutter and one exhaust fan?

Ah, the heat exchange idea. Sounds like a great thing to have. I'm done with heavy equipment in the area and not sure if the existing trenches are deep enough and long enough to make it work. Here's the data: The greenhouse will have apx. 1600 cubic feet of interior space. There's 25' of trench on the exterior of the north wall that's 4' below grade. Was planning on putting the French drain down there but could possibly add heat exchange tubes down there before backfilling also (see any reason why not?). If so, the tube could probably be doubled back on itself which would give another 25' of length. From there it could run along the trench outside the east wall, which is another 15', though only 2' below grade. From there it could run out a 15' trench (under a berm) that the French drain will run out. There will probably be around 3' of fill over that. So if that last 15' run is double with the pipe coming back to the greenhouse that would add another 15'. So the total would be roughly 25 + 25 + 15 + 15 + 15 = 95', with about half of that being 4' under grade and the other half about 2-3' under. Being in zone 5a the frost likely goes deeper than at your place. Is there some kind of equation to figure out if this would provide enough of a heat exchange? (The photos show the trench along the north wall and the trench through the berm that the French drain will run out to.)

Thanks again for you help with this! Your advice and the links to the specific items were really helpful.

You can use both. The BJ57 is better than insulation, no seams for water to get through, and has a rubber consistency. You would put it on the outside. I used it on my original chicken coop floor in 2013 (now a tool shed). It's still in pretty good condition considering it is being walked on now. Insulation would be applied outside after the BJ57 to help to not lose heat through the concrete. You don't necessarily need the BJ57 if you use foam board, but the BJ57 offers no insulation.

Ceiling fans would help keep the heat lower in the winter. Reverse them in the summer (if possible), and if you have a roof vent or vents, pulling up the hot air will help vent it through the roof vents. A lower intake vent could help that process by creating a chimney effect. Two fans in the opposite directions (2 doors?) would be helpful, too. I would try it and see - if you are trying to save money on more professional equipment or want to wait and figure which higher end units you will eventually want to use. I can tell you from my first, smaller greenhouse, portable fans and/or non-greenhouse specific fans means extension cords and less fan life since the average fan is not meant to function in high humidity like a greenhouse. They won't last as long. My experience is 1 year from a cheap fan, 2 years from a better fan, but many years from a fan designed for a greenhouse. My first real greenhouse circulation fan is 4-5 years old and still going strong.

I have to tell you, I know a lot about greenhouses, but no first-hand experience with GAHT (ground to air heat exchange) systems or heat pumps that some use...just what I read and watch. If memory serves me, the ideal depth for a GAHT system is 1 layer of pipes about 6 feet down and another set about 4 feet down. I don't think I gave you this link or you may have already stumbled upon it on your own.

https://ceresgs.com/gaht-syste...

Here's another one about two ways to insulate. I may still do the Swedish Skirt insulation since it can be added after the greenhouse is built.

https://ceresgs.com/solar-gree...

The tendency I think when building your first greenhouse is to overthink it and thinking you can make it perfect the first time around. It's like building a house when you have never lived in one. Greenhouse growing requires a rather sharp learning curve. You and your new greenhouse will develop together as time goes by. Do your best, but you will see things you could have done differently, or might change like me, once you are actually growing in it for a year or two. Eight years and I am still learning everyday in my greenhouse. Most important thing is have fun!

Thanks for another really helpful response Jim. Really like the idea of reversible fans and I might try the Swedish Skirt method since the foundation's still exposed. Might be able to get a bunch of partial pieces of ICF, cut the middle plastic brackets off and use the foam for insulating the foundation and those wings that angle into the ground. It'll obviously be more labor intensive than buying full sheets of rigid foam but the price and the environmental impact will sure be less.

And yes, it's easy for me to get caught in the weeds of projects and forget to have fun with it. Need to keep appreciating that I'm damn fortunate to even be able to have a greenhouse in the first place.
Thanks again Jim!

Would love to hear from anyone on whether a GAHT system will be effective and worth doing considering:
I'm done with heavy equipment in the area and not sure if the existing trenches are deep enough and long enough to make it work. Here's the data: The greenhouse will have apx. 1600 cubic feet of interior space. There's 25' of trench on the exterior of the north wall that's 4' below grade. Was planning on putting the French drain down there but could possibly add heat exchange tubes down there before backfilling also (see any reason why not?). If so, the tube could probably be doubled back on itself which would give another 25' of length. From there it could run along the trench outside the east wall, which is another 15', though only 2' below grade. From there it could run out a 15' trench (under a berm) that the French drain will run out. There will probably be around 3' of fill over that. So if that last 15' run is double with the pipe coming back to the greenhouse that would add another 15'. So the total would be roughly 25 + 25 + 15 + 15 + 15 = 95', with about half of that being 4' under grade and the other half about 2-3' under. Being in zone 5a the frost likely goes deeper than at your place. Is there some kind of equation to figure out if this would provide enough of a heat exchange? (The photos show the trench along the north wall and the trench through the berm that the French drain will run out to.)
Thanks.

leon6 said: Thanks for another really helpful response Jim. Really like the idea of reversible fans and I might try the Swedish Skirt method since the foundation's still exposed. Might be able to get a bunch of partial pieces of ICF, cut the middle plastic brackets off and use the foam for insulating the foundation and those wings that angle into the ground. It'll obviously be more labor intensive than buying full sheets of rigid foam but the price and the environmental impact will sure be less.

And yes, it's easy for me to get caught in the weeds of projects and forget to have fun with it. Need to keep appreciating that I'm damn fortunate to even be able to have a greenhouse in the first place.
Thanks again Jim!

That foam could work, but it's hard to tell from a picture. Do you know if it is closed cell or open cell foam. From a price standpoint, try to make use of open cell foam since it is a less expensive product that has the identical efficiency and comfort as closed cell (assuming same R-value). On the other hand, closed cell foam is stronger, stands up to moisture better, and can reach high R-values in a small amount of space.

I like you attitude about being grateful to have a greenhouse, and I can relate to getting "caught in the weeds of projects and forget to have fun." I am getting better at it, though, I think.

On your second post about a GAHT system, I have no firsthand experience. All I know is what I have read or watched. The GAHT system is not unique; it is the Ceres "brand" of ground/air heat exchange. Almost all similar systems recommend going down 6 feet. Are you going to be able to get down 6 feet. If you can't get down 6 feet, it will not be nearly efficient. It is at that depth the earth stays a constant temperature all year. That is what you want.

Thanks again Jim - really appreciate your responses!