Greenhouse renovation feasibility.
 

Hello All,

I am still finalizing my greenhouse renovation project. I wanted to run this plan by the orchidboard to make sure it is feasible and structurally sound.

I plan to excavate 4 inches or so and level the greenhouse floor (which is currently topsoil) and fill it with 3 inches of sand and top it off with pavers.

Some people have told me I would need partially buried retaining walls under the perimeter of the base (my base has metal footers that go into the ground rather than an underground foundation) to do this so the sand doesn’t escape from under the base of the greenhouse as I will have to dig around it. Is this true? I don’t think I could add this type of retaining wall as the metal footers on the base would obstruct the installation of a retaining wall.

I also need to make sure there is no gap between the base and the ground/new floor as I can’t have cold air getting in during the winter. As you can see in the photos, I already have a problem with gaps that need to be fixed. No matter how much extra soil I put, they also seem to reappear.

I have attached some photos of the base and a link showing the blueprint for my greenhouse’s base for visualization purposes.

Link to base:

https://grandiogreenhouses.com/manua...r_feb_2016.pdf

Stars---- so, the metal base of the greenhouse is literally just sitting on the bare ground? There is no type of foundation support or barrier? What are dimensions of the gh? Do you use this year-round in upstate NY?

There are two issues here.

For the interior 'floor', you are essentially building a patio. Ordinarily you need:

• 4-6" of crushed stone, tamped down
• 4-6" of sand, tamped down
• Pavers (which are 1.5 to 2" thick)

Since this patio won't see frost, you can get away with less. I am thinking 2-3 inches each of stone & sand.

Since the frame is sitting at grade level, you have a sealing issue. An easy fix would be a row of bricks, sitting vertical in the ground and extending about an inch over the bottom of the frame. This will also solve the erosion, if it was caused by watering inside the greenhouse.

If the erosion is due to rainwater run-off, then you need to deal with it from the outside. One solution would be sinking a 2x6 pressure treated board about 4" into the ground, 3-4 inches away from the base, and then filling the channel with pea gravel or similar.

Schematic attached is not to scale.

I think you could do a couple of things to help.

First, after you excavate, simply lay something on the metal foundation that goes over the inside edge down into the hole you've dug (the gray in the attached sketch). Landscape cloth would work to keep the sand in, but something like neoprene foam would also be insulating.

You might also consider using an expandable urethane foam in those metal channels to insulate even more.

i agree with Kim and Ray, great stuff makes a mix at home foam kit for big projects and that is what i would fill the gap with....since there is no frost i might consider using gravel all the way down and no pavers.

it will be a lot more forgiving and cheaper, it will prevent any issues with drainage and is a big step up from the dirt

if you want the pavers, you need sand...they will never be level (or even close!) without it

Yes, that is correct. The metal base sits at grade level with metal footers buried into cement pockets dug 10 inches down. It is thankfully very sturdy at least as it didn’t budge an inch with the latest storm.

The dimensions are 8x12 feet. I do use it year round. Thankfully it doesn’t get that cold in southern Westchester compared to truly upstate. I am just a few miles north of the New York City line so I am in the last mile of growing zone 7.

---------- Post added at 01:59 PM ---------- Previous post was at 01:44 PM ----------


Thank you all for the graphics, they are really helpful.

I just have a quick question about Ray’s graphic:

Is the foam or landscape fabric supposed to be the gray in the sketch?

Or, should I be also looking for some kind of L-shaped metal or plastic sheet to fit in that spot along with the foam/fabrics?

As you can tell, I had to call the greenhouse kit manufacturer hundreds of times to explain steps on graphics. I made them crazy.

Hah! That was my intention... The idea being that there is something to overlap from inside the metal channel down into the recess you're going to dig to provide a "seal".

A rigid L-shaped piece would be better than fabric, but I wouldn't use only a piece of metal, and that conducts heat really well.

If I was doing that, I'd likely buy some neoprene foam, 1/4"-1/2" thick, and glue it to the inside bottom of the channel, then fold it over at 90° downward and use the fill sand/gravel to hold it in place. Covering that with a vinyl or metal L-shaped piece would protect it and make it look nicer.

If you wanted to provide even more insulation, I'd fill the channels with a foam-in-a-can product like "Good Stuff".

The spray in foam others have suggested is exactly what I was thinking and I'd extend the pavers under the metal walls so there is no longer any contact between the metal base and "dirt", if you can. It will protect the metal structure better and with the foam give you better insulation and intrusion protection.

Keysguy, I like your idea for the pavers but I think I can only extend the pavers under the base 1/4 inch in max as the footers block them going all the way through.

Ideally, I would have had bricks go completely under the base so no ground is touching it but I think that’s impossible.

Fair orchids has made a very good drawing showing the metal footer problem. Additionally, I have even less space between the footers and the base than the drawing would suggest as there are very large nuts around each footer.

In other words, I can’t really push a paver through under the base unless I cut them into very bizarre shapes and then piece them together after installing them around the footers which are spaced every two feet. It’s like having to tile around a pipe so I guess it could be done but it does seem like a rather daunting task.

---------- Post added at 01:52 AM ---------- Previous post was at 01:45 AM ----------

I am just remembering that the inside bottom of the channel is filled with screws and bolts that jut up. They occur every 2 to 4 feet depending on the side. I think that may complicate things.

Remember the foam is degraded rapidly by ultraviolet light. This begins in minutes. It needs to be covered as fast as possible. I repaired woodpecker damage in my foam roof in spring 2019. I worked around dawn and dusk so exposed foam never saw the sun.