Building a greenhouse? Foundation question...

[Melensdad]

I want to build a lean-to style greenhouse on the back side of my garage/workshop. STILL IN THOUGHT PROCESS STAGES. The long wall will have a western exposure. Looking at 8' by 20' for the size. The ground is pretty darn close to flat, but just enough slope away from the foundation to allow for drainage.

I'm thinking that I will hit the grass with killer, then dump some crushed limestone on top a couple inches thick for stability. drainage and to make it easy to level, then use pressure-treated lumber for the foundation. The new pressure treated lumber is non-arsenic and rated for ground contact. Probably drill a few holes in the PT lumber and drive down some re-bar to act as an anchor.

Does this seem reasonable?

 

[FrancSevin]

I want to build a lean-to style greenhouse on the back side of my garage/workshop. STILL IN THOUGHT PROCESS STAGES. The long wall will have a western exposure. Looking at 8' by 20' for the size. The ground is pretty darn close to flat, but just enough slope away from the foundation to allow for drainage.

I'm thinking that I will hit the grass with killer, then dump some crushed limestone on top a couple inches thick for stability. drainage and to make it easy to level, then use pressure-treated lumber for the foundation. The new pressure treated lumber is non-arsenic and rated for ground contact. Probably drill a few holes in the PT lumber and drive down some re-bar to act as an anchor.

Does this seem reasonable?

Yes. Quit reasonable. Some thoughts;
Use 1.0" limestone about three inches deep minimum.
Run some PVC drainage pipe every two feet from the garage wall past the foundation. Be sure to put socks on them.
You can connect them all to one drain coming out from the foundation.

Be sure there is 3.0" as a drain base under the treated timbers.

You will have critters digging under the foundation so put down Chicken wire mesh as well.

I would use 8'X8" treated for the foundation. 6" would also work.

Inside, over the gravel, place 16"X16" precast concrete for walkways

OR do an interlocking key brick for the floor.

I have interlocking "KEY" brick and it drains very well.

Since you are putting it on the south wall, consider a window or two to the garage. I use my south facing greenhouse to heat my home in winter. In summer deciduous maple and redbud trees provide shade, keeping the room cool.

 

[chowderman]

if you're going to use glass, no. glass does not take well to foundation heaving/movement.
this was Valley Forge area - block foundation below frost line . . . went with tempered glass since we had youngsters at the time.

 

[Melensdad]

Thinking of using a combination of some recycled glass windows with some 'twin cell' 4'x8' polycarbonate panels for the glazing. Putting in a patio door for the main exterior entry door.

 

[mla2ofus]

I set my greenhouse on RR ties leveled with my water level. drilled angled holes thru the ties and drove 3' rebar thru them. Have a 6' slider and four used aluminum frame horizontal sliding windows in the south wall and polycarbonate panels in the east wall and poly panel and aluminum storm door for entry. Haven't had any binding on anything.

 

[bczoom]

A friend of mine just built a nice greenhouse. For the polycarbonate, he went with this place and they took good care of him.

Cut To Size Polycarbonate Sheets - ePlast.com

Easy to install and low maintenance polycarbonate sheets made in the USA and delivered to your home. Best solution for roofing, greenhouses, pergolas, room divider, desk divider, light diffuser and more.

www.eplast.com

He went with the 8mm double wall and got the UV protection on one side.
My friend said "They are very responsive and will talk you through their products with no rush if you call them for ideas."
He got the channels elsewhere but didn't mention where.

For channels, glass and polycarbonate, also look locally. I see the poly on our local craigslist pretty frequently. A local glass shop may be a good source for products. For your size, they may have what you need in their spare parts section.