I am trying to build a tropical greenhouse. My first time trying it.

So, I bought the "Palgram Glory 8'x12' greenhouse

My zone is 7a.

My goal is to keep the greenhouse at least 65F during winter.

Do I need to build/insulate the floor? I was thinking that I need to insulate the floor. So, I plan to put a 2 inches layer of foamboard, then 2-3 inches of pea gravel layer on top of it, then 1-2 inches of sand, and finally 2 inches of concrete block.

Would that be enough to insulate the floor?

I try to minimize the cost of heating as much as possible. But, in the event that I need to heat to keep it above 65F, I will use a space heater.

Can anyone provide me any advice on my plan? Is it feasible to have this tropical greenhouse in my zone 7a?

Would my floor insulation plan good enough?

Thank you.

Its not the floor you have to worry about, its the walls and roof. The ground temperature inside the greenhouse will be determined by the air temperture inside the greenhouse. Sinking an insulated stem wall below the foundation will help keep cold from coming in from the sides.

With twin wall its going to be difficult to maintain an air temperature of 65. You may want to look into greenhouse bubble wrap. Heating is going to be your biggest expense and your biggest problem.

The gravel/sand/concrete block makes a good floor. Tropical greenhouses are wet places and floors that drain well are important. Make sure you have a dry spot for your heater.

Why 65? I grow orchids and try to maintain above 55.

I hope that you have a large bank account!! The cold air of winter does not seep in from the ground. It is just like Daisy said, heat is your biggest expense. The more you layer the walls and the roof, the more money you save.
I had a greenhouse that was 300 square feet in zone 7 on Long Island. My floor was 4" of rolled builder's sand. it is extremely important to get it level. if you choose a greenhouse with 4' or 5' sidewalls, if you could dig it out to 2-3' deep and have it half way below ground, that will save you big $$$$$$. Ground/Dirt is a very good insulator!!

If you cover all of the remaining sides with Bubble wrap made for greenhouses like Daisy suggested, that will help. My greenhouse was double paned glass with a winter cover of 6mil plastic covering the walls and roof. The plastic was held away from the glass by using 1" x 2' lathe. I laid it on it's end creating an air space. This meant that it would hold heat a little better. AND IT STILL COST AN ARM AND A LEG to heat it!!! But that is the commitment you make.
You'll save even more shooting for 60 degrees then 65. better yet, 55 instead of 65. Every degree lower saves you money. That and you'll need Life Insurance when you LOOK AT THAT FIRST BILL in case of a heart attack.

In your case, it is so much better to overbuild something then to under build!!! Like Daisy, mine was benches along the outer walls with wood chips for humidity and I always had trouble keeping that humidity UP!!! The winter heating dried the greenhouse right out. I grew 98% orchids in mine like Daisy.
A very dear friend of mine grew VANDAS, tropical orchids form Southeast Asia. They {the Vandas} hated anything below 65 degrees! Hated it. She made the biggest sacrifice paying those winter electric bills. She used to say that she could hear cash register noise all night long as the heating costs mounted up. HER SOLUTION WAS TO MOVE TO CENTRAL FLORIDA! She saved a ton of money that way.
I am in no way trying to talk you out of this but telling you to carefully plan everything out. And remember that once you finish, a full greenhouse is cheaper to run one that is half empty. Oh, lastly, have a good back up plan for heat because at some point, it will be real cold one night and the power might go out. I used a supplemental heat for really cold nights in the form of a kerosene heater, running that baby on a low setting kept the green house at 62 degrees. Normally it was 55.

Welcome!
Wow, I run two greenhouses, one for tropical and the other is our Brugmansia House 12 X 10 feet. We run two heaters set at 65 degrees in the brug house with thermostats, which we can monitor from the kitchen window and have a control to raise or lower the temp. The other is a 8 X 10 where the tropical are housed and that one runs a heater with a thermostat also, set at 70. Both greenhouses have a 55 gallon rain barrel for watering which helps keep the heat when we have a power outage. They keep the heat so other heaters can be put in place. We are zone 8b. You will figure out what is best for you. Our floor is gravel based and we toss a couple tarps over them in the winter months.

Karma, mind telling us more about the heaters you use [gas, electric, propane] and what they cost to run?

jpm995,
This is our first year with these two electric heaters after my other heaters purchased at a Big Box store went out after 6 years of colder than normal weather. This year we have only had a week of
really cold 20s degree. But we are about to get cold again, so I'll kick the heaters up after turning them off for a week during the day and the doors are open. Our electric bill is divided into 12 equal payments, and it's been around $230 a month. We also have a brand-new heat pump so our cost for heating the house really dropped this last year. We live in the valley floor with mountains around us, so our weather is mild here. We also double tarp both greenhouses to help keep the heat in besides using 20 MIL on the brug house and it's up under the eaves on the shed in a protective area. I try to cut the cost for my addiction wherever I can. Hope this helps.

Have a little more time to add to this. Hunter was the Big Box store heater; it didn't have all the bells and whistles that the Lasko have and much smaller. Lasko can be found at Walmart, there are several varieties so read the boxes. This wasn't my first choice, but they didn't have the one I wanted.

Thanks Karma, glad to hear the heat pump is very economical. It's what i'm planning to use on the shed and greenhouse. The ones designated 'cold climate' are supposed to be efficient to below zero. I figure i'll use the wood stove as backup and really cold nights. We were in the teens here on Long Island the last few weeks thankfully it's warmed back up to around 30 at night. The brug's beautiful when in flower, a greenhouse in Connecticut [Logee's] has some and their stunning and the smell is wonderful.

jpm995,
I can tell you there is a world of difference between the heating unit we had and the now 1 year old heat pump! The folks about fainted when we showed them the furnace, it seems that the unit was something that they would use in AZ not WA State. We have a 4 bedroom house and they were surprised we could heat it! Our house was built in the early 70s and it was the builder's home. Let's just say he took a lot of shortcuts. The new heat pump folks had a hard time finding a spot for it as the yard is beautifully landscaped!! The even brought in the machine and sealed all the leaks. What a world of difference in the electric bill!! Then there are the rebates!!

Oh to visit Logee's, they are on my bucket list!! I was lucky to visit Terra Nova Nursery, they are the one that created B. Snowbank, a tissue culture. The mother tree was so impressive and Dan the owner, was so generous with his advice when we visited. He got me started with Clivias!! He just
laugh at me for digging up my back yard and planting my whole collection of 136 varieties. I have really cut back since those days.

Hi @Shonick and welcome to the forum!

OMG. Palram greenhouse in 7a at 65 during the winter. Good luck because you are going to need it. By the time you pay for all the insulating tips and tricks and the electric bill for a season or two, you will probably spend more than you paid for the greenhouse. Don't mean to rain on your parade. Just being realistic.

Insulate the floor. Sinking an insulated wall around the perimeter as Daisy said will be a big help. If you can't do that, look at creating a Swedish Skirt. (https://ceresgs.com/solar-gree...) Bubble wrap will help on the south/west walls and south roof. I would go with a reflective insulation that incorporates bubble wrap on the north and east walls and north roof. (https://www.homedepot.com/p/Re...). More expensive than bubble wrap, but better insulation and solar/heat reflection. Seal, as much as you can, any spaces you find in the structure. Use energy efficient heater(s). My choice is those oil-filled radiator-type ones. 8x12 doesn't give you much room for something like 55-gallon drums with water (painted black). A few milk or water jugs won't do much. Finally, if you are a praying person, start now; you are going to need all the help you can get.

Here is a short video of what I did for two seasons to help. I eventually dismantled it because it took up so much room, but it helped a lot. (I now grow indoors using grow lights during the winter.) You might be able to get some ideas from it. https://rumble.com/ve0p8p-sola...

Please do let us know how you proceed with pictures. (We love pictures here!) Ask questions. There are a lot of knowledgeable folks here that have been there, done that, and own the T shirt. Tell us what works and doesn't work for you. It is possible to do what you want, but it is not easy or cheap.

Jim

Karma, going to Foxwoods Casino in Conn. on Monday will make my usual stop at Logee's. My wife thinks i go to gamble but wandering through the greenhouses at Logee's is my real reason to go. I'm looking into a mini split heat pump for the shed but will probably have to run a 240volt line to shed which will be a pain. I hope i can get everything done, it's been a dream of mine for a very long time.

jpm995,
Take lots of photos to share, please!! I bet you could spend an entire day there. : )

When we put in the new electric line to both the greenhouse and Brug House we did the 240 and
also updated the electrical panel in the garage. I loved the look on the State inspector when he
came out, he asked if I was going to grow MJ?? I just laughed and said something much better!!
That fall he stopped back by to ask where all the plants were? The brug house and greenhouse doors were open and I told him to take a look and that poor guy about fainted. I think now he understands why the upgrade.

I think most 'normal' people don't understand the depth of our addiction to plants. My wife can't understand why I don't just get plants from Home Depot. Why do i have to use mail order or go to Logee's? Their just plants.

DaisyI said:

Sinking an insulated stem wall below the foundation will help keep cold from coming in from the sides.

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?

karmahappytoes said:
Our electric bill is divided into 12 equal payments, and it's been around $230 a month.

Did the $230 a month cover only your 2 greenhouses or that include your house electric?

BigBill said: . My floor was 4" of rolled builder's sand. it is extremely important to get it level.

What do you mean "get it level" here?

Shonick,
That is the house, the two greenhouses, shed and all the lights at night.

jmp995,
She sounds like my DH!! HD has nothing I don't already have and for the last 4 years I just
look and don't buy! Give me a good trade or a shop online and I'll be happy!!

Thank you everyone for helping out. I would say, it was too much information. I'm still trying to put them together...

I haven't done much building this greenhouse due to cold weather in the last few days.

The goal is to minimize the heating cost.

I'm trying to maintain a minimum 65 F degree because I will have tropical aquarium fish ( such as Guppy) and tropical plants in this greenhouse.

I'm trying to weight on the pros and cons on the option that I have currently.

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.

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?

3) I will definitely insulate everything I can where it is not tight on the greenhouse.

4) I know with this setup, I will need a heater. But, without the actual greenhouse up and running. I can't do an accurate calculation on the heating enegy that I need. If anyone in the zone 7a and have a similar setup such as 8' ×12'. Can you let me know how much Kwh per month needed to heat in the coldest month? Understand everyone setup is different, but an estimate would help. Costing an arm and leg doesn't tell me much 😂. I'm a technical guy. I do well with numbers than words without number.

Thanks everyone for help.

Shonick, have you installed the greenhouse yet? If so it's a lot of work to build footings and foundations under an existing unit. It seems very cost prohibitive and i doubt it will make a big difference. I think the best you could do is make sure there's no air leaks and wrap the GH with film or something that will hold up for the winter. A small electric heater will be costly to run and won't get you to 65 degrees on cold nights but your options are limited.

Your greenhouse should be bolted to a foundation, much like a house foundation. The foundation should be deep enough to reach below the freeze/frost line (at my house, that's 18 inches). The outside of the foundation should be insulated to keep the cold from coming in. Then the temperature of the floor will be determined by the temperature of the air inside the greenhouse. It will still feel cold but not as cold as outside.

The floor in my current greenhouse is concrete. But my old greenhouse had a paver floor. Its was essentially built like a patio inside a greenhouse. Whatever you use: gravel, sand, pavers, concrete, (not wood), it should be level or your benches and pots will sit wonky and it should drain exceedingly well. Don't put anything under the floor that will impede the flow of water downwards. My concrete floor is slightly sloped toward drains on the edge of the wall with a French drain outside to carry water to the street.

Jpm995,

I have not installed the greenhouse yet. I did the concret footing (6 pillars). It is not the whole foundation though.

The reason I built the 6 concret pillar is to prevent the greenhouse collaps incase of big wind ( my area does not have big wind though).

I didn't think about foundation and insulating the ground when I started.

After I do learned about this forum and everyone seems to care about much insulating the floor and ground.

If insulating the floor and ground is important like digging 4 feets, I will have to start digging. That is a huge huge effort, and I'm not sure if it make much different if I just put a layer of concrete block on the floor.

I think the insulated foundation wall won't help at all at 6". Your chance at success will depend on how much heat [from the heater] you can keep from escaping the GH. Some GH makers list how many btu's it takes to achieve temps depending on your zone. If you can find that it will give you an estimate on the size of heater you need. The cubic feet [not square feet] of the GH determines this. Will need to size your heater for the fish tank also to adjust the delta between GH temp and water temp.