Building a Foundation Question: Building a Greenhouse

[Groesbeck Hurricane]

OK, I am finally ready to start breaking ground on our new greenhouse. It will be built with doors and windows from other projects, friends, neighbors, re-store, etc. I have the lumber collected from a local sawmill and auction buys. Needless to say, this is NOT a kit and I don't have the bucks to spring for one!

I am working through the foundation in my mind and wanted to run this past some other minds.

Size is 16 x 24 or 32, still debating a bit on this one. Central Indiana is build location.

Post building as basic. Put treated posts (ONLY treated lumber I plan to use) 48" in the ground, standing 8' up. Dig trench 14 inches wide and 18 inches deep around perimeter. Fill in post holes and trench with gravel #1 (I have some of this just lying around).

Lay on top of gravel at ground level 4 x 6 cedar and tie it into the treated posts. Clad with wood, 1 x 6 to 1x 8 and insulate.

I have much 2 x 6,8,10,12. Did I say alot? I have more of that than 1 x material though the mill has some 1 x laying around they will make a deal on.

I will not use RR Ties due to the chemicals, I will NOT poison myself. I hate treated lumber around food products but do not have cedar posts.

Maybe I should buy some 4x6 cedar posts for this specific project? Need to keep costs down, though.

Any thoughts suggestions are welcome! I have a small tractor (60HP) with FEL to help with the project. Lots of nails and screws from auctions, all of it pretty new, and a really nice nail gun and staple gun.

Need paint....

[JoshB]

Here is what I did for a foundation - course little different weather down here in the south

[john70t]

Not a builder, but this is not a good plan, IMO.

Vertical lumber set in stone will eventually settle and shift and tear the building apart. A stone perimeter trench will eventually settle, and everything above the sill plate(walls, windows, roof) will drop at that spot.
The stone will always try to leave downhill.
Additionally, stone trenches and holes acts like a bowl of collected water to be absorbed by anything nearbye.

I'd suggest(at a minimum) a shallow concrete perimeter foundation with pilings 4ft deep. We are in a frost zone so heaving of the ground will destroy everything not tied in.

The width, number, and location of the pilings and the dimmensions of the perimeter foundation wall will be based on the load calculation of the weight of the materials above it.
A taller foundation means less likelyhood of water splashing onto wood and/or insects invading.

It is probably governed by local code and will probably require a permit as a occupied structure. You don't want a wall of glass falling over with people inside. They may go after you for taxes later if an inspector sees it.
(The concrete people may not pour without a permit as well.)


At a DIY minimum, get a large diameter post hole digger for the concrete pilings and make a frame for the concrete perimeter tied into these with rebar. Remember to have the Simpson hardware attachments mapped out for securing the wood.
Add 3/4 stone and compact everything before a pour.
Level, level, level.
Trench a perimeter drain around the foundation that leads to a pit(drywell) and a lot of freeze/thaw and furthur rot issues are solved.

[john70t]

Treated lumber chemical formulas have been changed since about 2003, AFAIK. Wood preservation - Wikipedia, the free encyclopedia
The CCA is no longer permitted for residential use(box store customers) and I think they use a copper-based chemical called ACQ to coat the outside but not cut ends.

Sill plate should be made of this at a minimum with some kind of barrier underneath to keep moisture from wicking up. Any wood next to ground or concrete will act like a sponge.

[MotoSook]

Anchor posts in concrete, no need to footer wall. Use 8" or 10" sonotubes and go 36"+ with the concrete. If you're worried about it, you can just put in the concrete tubes and the use anchor bolts to tie the walls down to the top of the sonotubes.

I've installed far heavier buildings on sonotubes spaced every 4 feet. The soil in Midwest will be fine unless you are in a swampy area, then you have to go deeper or bring in fill.

[flatbutt]

16 X 24 is a fair size. I built a free standing deck that is close to that size and I put in sonotube pilings every four feet at a depth of four feet. Then I laid the framing on top of that.

[Burnin' oil]

I don't deal with frost heave and issues like that, but as a rule I do not like burying posts in the ground because of the inevitable rot. I use post anchors in concrete.

[Zeke]

The posts set in the ground 4 feet will help with the wind load. If you do use anchors on top of concrete at the surface, design cross bracing to keep the thing upright.

[Groesbeck Hurricane]

Posts in ground are for wind load. I was going to slope the roof only to the West as that is where 95% of our weather comes from (I am in a valley).

Had not thought about the settling of the gravel. I only have three to four feet of top soil and then it is limestone, hard rock! Gravel was also to discourage moles from entering the tasty area.

Could gravel still be used to discourage critters and use pilings to support the structure? I was thinking every four feet but is that good enough? Of course, I'm not working against hurricanes! Oh, I do have lots and lots of strapping material! I have built several pole barns before and they are all still standing, some were built in the early '90's in tornado country in Texas.

Good points, thank you! What about setting re-bar/steel (happen to have some of that "just laying around") into concrete, attaching the sill-plate to that as an anchor and then going up from there with the posts?

I will research out sonotubes. Wonder if Menard's would have them?

I need large to produce food for sale and personal use. Also want a couple of banana trees and maybe a rose apple tree. Heat with wood fire, add water to top of unit to keep humidity up, fresh foot in the winter. It is a plan, now to find out if it will work ;-)

Please, more ideas are VERY welcome!!!!