Wow you did a good job with the pillars. I've seen some GH makers recommend mounting these on decks or even 3" concrete pads. One thing to remember these are cheaply made greenhouses [due to low price]. You could bolt these down to the earth's core but a 70-mph wind probably rips the GH away from the foundation. I have a 10x10 Lowe's plastic shed. I made a platform of 2x6's screwed the shed to that and used screw in ground anchors on the corners. It's been rock steady for over 5 years in storms with over 50mph winds. Most hobby GH's are considered temporary structures and don't require proper foundations. Your biggest issue will be heating a free-standing GH with twinwall poly to 65 degrees in your zone.

Shonick said: Can you elaborate more on this? Are you saying, adding an insulated wall below the foundation, meaning to extend the greenhouse wall into the ground?

Take a look at the first picture in this article. https://ceresgs.com/solar-gree... Of course, this is an extreme example, but you will get an idea of sinking and extended, insulated wall. This type of wall will keep the cold from the ground from getting under your greenhouse. If the sunken wall goes down to the frost depth in your area, you actually can take advantage of the constant warmer ground temperature under the greenhouse with this type of wall, or the easier Swedish Skirt mentioned further down in the article.

See comments (caps)

Shonick said:

1) First regarding to the floor, I understand that the wall is best to extended to 4' into the ground. But that is a lot of digging. Would 6" extended (wall) into the ground work? I will also put a concrete block on the floor. Would that reduce the heat loss to the ground? I prefer to have less digging if it is possible.

NO. 6 IINCHES WON'T DO IT. THE FURTHER DOWN YOU GO THE BETTER. CHECK OUT THE SWEDISH SKIRT MENTIONED IN THAT ARTICLE. MINIMAL DIGGING. MIGHT BE AN ALTERNATIVE OPTION FOR YOU.

2) For the wall and top, I will start adding the greenhouse bubble wrap on the inside of greenhouse. I'm not sure about the thickness yet. Could 6 mil greenhouse bubble wrap thick is enough? Should I add another layer of bubble wrap on the outside of greenhouse as well?

THE MORE BUBBLE WRAP THE BETTER. THE AIR IN THE BUBBLES IS WHAT PROVIDES THE INSULATIUON. (THE REFLECTIX ON THE EAST AND NORTH WALLS/CEILING THAT I MENTIONED, WILL PROVIDE MORE INSULATION THAN BUBBLE WRAP ON THOSE AREAS AS YOU WILL NOT GET ANY GAIN FROM THOSE DIRECTIONS.) BUBBLE WRAP ON THE OUTSIDE WOULD MOST LIKELY GET DESTROYED IN THE WINTER WEATHER. I HAVE HEARD OF PEOPLE USING AN INSULATED, CLEAR POOL COVER ON THE OUTSIDE. MUSH MORE DURABLE. (THINK OF IT AS HEAVY-DUTY, RUBBERISZED BUBBLE WRAP.)

Just another option for anchoring your greenhouse...I have my 8x16 sitting on and bolted to true 6x6's cut from Black Locust that are sunk into gravel dust (2 - 8' lengths, 2 - 16' lengths). Black Locust is an extremely durable (no preservation needed) and extremely heavy wood. The greenhouse could get blown down before the foundation would move.

MoonShadows said: Take a look at the first picture in this article. ceresgs.com/solar-greenhouse-basics-insulating-your-foundation/ Of course, this is an extreme example

If I follow through this, I would dig it more than 5 feet. My frostline is at 30 inches. The temperature is constant at 2' -3' below the frost line. So, I would have to dig more than 5' to be perfect 🤣.

It would take me a long time to dig and get this greenhouse installed. I do it by myself.

So, that why I try to find an alternative way with minimize digging.

Instead digging too much. Can I just insulate the floor using reflective foam or EPDM rubber, then put a layer of paver/concrete blocks on it?

Of course, the insulation will be everywhere on the floor and touch the wall that is in the ground like 6" - 12" deep.

Since it is in the ground, I'm not quite sure if reflective foam or EPDM rubber better? I look it up a bit, it advertises that the reflective foam will not be disintegrated. But I'm not sure how it reacts when I put underground for years.

For the heater, I did the rough calculation using the cubic area of the greenhouse and estimated the heat loss. I came with a number that I need 1.3 kwh enegry for a night on the cold day.

Not sure if this number is too low. Maybe it is. Too many variable for the calculation while I can't measure it yet. It is hard to be accurate.

Once I built it and measure all the variable, it would be straight forward calculation though.

Shonick said: If I follow through this, I would dig it more than 5 feet. My frostline is at 30 inches. The temperature is constant at 2' -3' below the frost line. So, I would have to dig more than 5' to be perfect 🤣.

It would take me a long time to dig and get this greenhouse installed. I do it by myself.

So, that why I try to find an alternative way with minimize digging.

Instead digging too much. Can I just insulate the floor using reflective foam or EPDM rubber, then put a layer of paver/concrete blocks on it?

Of course, the insulation will be everywhere on the floor and touch the wall that is in the ground like 6" - 12" deep.

Since it is in the ground, I'm not quite sure if reflective foam or EPDM rubber better? I look it up a bit, it advertises that the reflective foam will not be disintegrated. But I'm not sure how it reacts when I put underground for years.

For the heater, I did the rough calculation using the cubic area of the greenhouse and estimated the heat loss. I came with a number that I need 1.3 kwh enegry for a night on the cold day.

Not sure if this number is too low. Maybe it is. Too many variable for the calculation while I can't measure it yet. It is hard to be accurate.

Once I built it and measure all the variable, it would be straight forward calculation though.

If your frost line is 2-3', a 3-foot wall would make a big difference. Ceres is known for their "extremes" in designing/building their energy-efficient greenhouses. You just want to keep the winter cold at bay under your greenhouse.

Reflective foam would most likely get crushed in time minimizing your insulation factor. EPDM by itself will not insulate. I don't think I have ever read a recommendation for using foam board insulation on/under the floor in a greenhouse in any greenhouse literature. If it worked, I'm sure I would have read about it somewhere.

Did you look at the Swedish Skirt insulation method in that article? It would eliminate any deep digging, and it would keep the cold in the ground from ever getting underneath your greenhouse by insulating the ground around your greenhouse.



A 1,500W heater will consume 1,500 watts of electricity in 1 hour. That's 1.5 kwh per hour. In 24 hours, it will use 36 kwh. Multiply 36 times your electric cost per kwh (electricity production and distribution costs) and that will give you a cost per day if you run the heater 24/7 which you will most likely need to do on real cold and/or cloudy days. Here I currently pay about 13 cents per kwh, so my cost would be $4.68 a day which translates to $140.40 a month. If you pay more or less for your electricity, you will pay more or less per kwh per day/month.

I believe if you search, you can find a few greenhouse heat calculators based on length, width, height, outdoor temperature, desired indoor temperature. It will give you a rough estimate, but it will not account for other factors that may contribute to heating needs/losses.

I think the main mistake most new greenhouse folks make (and it is natural) is that they assume since it is a greenhouse, and a greenhouse is supposed to be a warm, cozy place where plants will thrive, is to think an out-of-the-box greenhouse is suitable for year-round growing in colder zones (and I include myself when I first bought my greenhouse), when in reality they are only suitable for growing in about 8 months a year (extending the growing season about 1 to 1 1/2 months in each direction) without high costs for retrofitting with insulative materials and the crazy cost for the amount of heat that is needed.

I think the next mistake most new greenhouse folks make is thinking they can re-invent the wheel in accomplishing all this when there are tried and true ways to create winter growing conditions in a greenhouse that isn't designed for winter growing. (Once again, I include myself my first couple of years.)

Out of the box greenhouse companies are very misleading on both the above.

Keep asking questions; that's how we all learn about this addiction! In a few years, you'll be giving new greenhouse owners good advice.

Shonick, where is your zone 7 with a 30" frost depth? I live in zone 6 and my frost depth is 18 inches. I doubt its even that deep but that's what the city says. I have an 18 inch deep pond and it doesn't freeze to the bottom.

Don't confuse frost line with how much of your pond freezes. Frost line is the depth at which groundwater freezes. There are a lot of factors that keep your pond from freezing to the bottom (warmer days, sun, etc.), but once the ground starts to freeze, it will keep going deeper and it most likely will stay that way all winter. It takes a long time for the ground to defrost. You may have early warm spring days with moderate temperatures, but just below the surface your ground will still be frozen. I am in PA Zone 6 and my frost depth for my soil is 44 inches, however I have an above ground fishpond that is 36 inches and only the first few inches on top ever freezes. After a couple of cold weeks where the temps were single digits at night and teens/20's/30's during the day, we had 4 or 5 days in the 40's/50's last week. I still couldn't even drive a wood stake in the ground more than 1/4" before the ground was like a rock, but my pond was ice-free.

MoonShadows said: If your frost line is 2-3', a 3-foot wall would make a big difference. Ceres is known for their "extremes" in designing/building their energy-efficient greenhouses. You just want to keep the winter cold at bay under your greenhouse.

Reflective foam would most likely get crushed in time minimizing your insulation factor. EPDM by itself will not insulate. I don't think I have ever read a recommendation for using foam board insulation on/under the floor in a greenhouse in any greenhouse literature. If it worked, I'm sure I would have read about it somewhere.

Did you look at the Swedish Skirt insulation method in that article? It would eliminate any deep digging, and it would keep the cold in the ground from ever getting underneath your greenhouse by insulating the ground around your greenhouse.



A 1,500W heater will consume 1,500 watts of electricity in 1 hour. That's 1.5 kwh per hour. In 24 hours, it will use 36 kwh. Multiply 36 times your electric cost per kwh (electricity production and distribution costs) and that will give you a cost per day if you run the heater 24/7 which you will most likely need to do on real cold and/or cloudy days. Here I currently pay about 13 cents per kwh, so my cost would be $4.68 a day which translates to $140.40 a month. If you pay more or less for your electricity, you will pay more or less per kwh per day/month.

I believe if you search, you can find a few greenhouse heat calculators based on length, width, height, outdoor temperature, desired indoor temperature. It will give you a rough estimate, but it will not account for other factors that may contribute to heating needs/losses.

I read the whole article and I understand it. In order to achieve any of that design. I have to dig more than 5 feet to achieve that.

I also see that they use foamboard underground. Not sure how long it will last. Without technical knowledge on the property of the foamboard, I though the reflective foam is much better since it has aluminum cover.

I'm not talking about heater Watt when I refer the kwh in my early reply. It was the total energy in kwh per day in my reply. 😂 I guess I underestimated the heat loss.

I used to stay in my car during cold day for hours without turning the car. I don't think the temperature in greenhouse will drop more quicker than that in the car. That is why I came to that estimation unless I am totally wrong and my number screwed up. My estimate is only for the night though.

I used math and physic and heat transfer property, etc... to calculate all my estimate. It could be that I don't use that much physics math in 15 years, I may miss out some important variables.

I used total energy needed because it is the number everyone should care about vs heater W or electric rate. Everyone can use different heater or having different electric rate. But the total enery is the same for the exactly greenouse at the exact location.

I'm in Maryland zone 7a. Frostline is 30 inches. I can't post link yet, but if you search for Maryland, you will see it say 30 inches for frost line.

So, can you help me estimate my enery cost in kwh or J or how much you pay in your electric cost for greenhouse and your electric rate instead of telling me it will cost an arm and leg? When I have that kwh or J , I will see how big it is.

You can tell me the rate at the temperature drop in hour. Or on the cold day, your highest temperature during the day and how it drop during the night.

I tried to search over the internet, but I can't find much information regarding to the enery cost in any units such as money, total kwh per day, or in J.

I know it is a relative number to the design. But it is good to know their design and their number.

I know I want to do it perfectly on the first try. But it seems, I don't have much data at hand to do it. I believe many of you are the same when you first started, build, collect data, then do the improvement.

Look like I will be the same because I can't get the hold on those important data. 🤣

I know I talked with numbers and most people don't do that in general. Extreme design is great to achieve the best result. But is that the most economic solution when cost, time, effort, and opportunity cost taking into account?

That is where I need to debate if I have to dig 5 feet. Digging 5 feet during this time of the year is so hard.🤣. I tried and I think it will take me a long time to get that done.

Shonick said: I read the whole article and I understand it. In order to achieve any of that design. I have to dig more than 5 feet to achieve that.

You keep saying you would have to dig down 5 feet. I don't know where you are getting that with the Swedish Skirt method. For the SS, you only need to dig down a few inches.

Quote from the article: "Also known as the "Swedish Skirt", this method can be used with a slab on grade, with piers if you auger the holes, or if you decide to use no foundation at all. The idea with the Swedish Skirt is that you lay rigid foam board horizontal starting at the base of the greenhouse, and extending 4' away from the greenhouse. This insulation needs to slope gently away from the greenhouse for drainage, which will require some minimal digging or raking. It's also best to cover this foam with gravel or soil, as direct UV rays will damage the insulation. Like the vertical insulation, this system also prevents frozen soil from creeping under the greenhouse, while keeping the warm soil where you want it, directly under your greenhouse."

Here's a short video of a guy who used the SS around his house:

There are others on youtube including a two-parter of the SS being used around a very large greenhouse.

Moonshadow, That's why I was asking where Shonick lives. We don't have feet of snow on the ground all winter. That makes a difference. One size doesn't fit all - zones are about air temperature only, not environmental differences.

I think its easier to answer questions when we know the whole story, not just the zone.

DaisyI said: Moonshadow, That's why I was asking where Shonick lives. We don't have feet of snow on the ground all winter. That makes a difference. One size doesn't fit all - zones are about air temperature only, not environmental differences.

I think its easier to answer questions when we know the whole story, not just the zone.

We don't have feet of snow on the ground all winter either. I know one size doesn't fit all. I agree with you with zones being about air temperature, not frost depths. Not sure what you are conveying to me in your post. Can you explain further? Thanks.

On the east coast, Crepe Myrtles can easily survive in Zone 7. In my area, they drop dead mid-winter. Knowing where the OP lives so we can understand climate, latitude, soil types... Would help us give more accurate answers. I'm suspecting humus and clay heavy soil freeze deeper. I live on a pile of sand in a very dry climate. Its hard to freeze dry sand.

I'm still not sure what that has to do with my suggestion for a Swedish Skirt. Perhaps I'm just missing your point.

It has nothing to do with a Swedish Skirt. It has everything to do with knowing where an OP lives so we can give our best advice.

DaisyI said: It has nothing to do with a Swedish Skirt. It has everything to do with knowing where an OP lives so we can give our best advice.

If you are talking about keeping Tropicals at 65 degrees during the winter in zone 7, whether he is in Maryland or somewhere else has little influence IMO and from most of what I have read when it comes to insulating/heating a greenhouse. If you have a source that says different, I would be glad to read it and learn. Thanks.

I'm wasn't really even talking to you. I asked where Shonick lives because climate and environment has a lot to do with freeze depth and foundation insulation. Still don't know the answer to that question but I give up...

Whatever...

I get the feeling like op is trying to decide on whether to buy a 12 or 16 oz bottle of water to put out a house fire. Digging a 5' deep foundation for a Palmram greenhouse would qualify for a Guiness record and accomplish little. He has some tough decisions to make, and he may be facing an impossible task. In my opinion finish installing the GH, use bubble wrap and anything else he can find to max out the installation, buy a heater and see what changes you have to make to go forward. My feeling is he will either have to bite the bullet and pay a lot to heat the gh or lower his expectations of what he wants to do.