# Foundation for greenhouse



## Ziptie (May 16, 2013)

* Gothic Solar Star Greenhouse Kit - Propane 26'W x 28' *

http://www.farmtek.com/farm/supplie...solarstar_greenhouse;pg106306sp_106306SP.html


Wanting to build the above greenhouse. Had a hill that was mostly rock excavated behind our house. I would like to put this greenhouse on a foundation (8X16 inches)and the north side of the greenhouse a 4ft wall (this is about how tall the hill that was excavated). No concrete on the floor of the greenhouse.



The ground is basically solid bedrock. Tried to get some guys to come pour the foundation and wall...didn't want to do the job,or they just don't call back,or say they will come but never do, or the best one yet they will do the job for $10,000 (I called the concrete company this job only requires about $600 of concrete).


So I was thinking maybe I should just do it myself with cinder blocks. Not sure where to start with the how. 



Can I put the cinder blocks right on top of the rocks to make the foundation (assuming I level the blocks with road rock first) or does it have to be poured concrete? 



Any good y-tube videos recommend? 



Pros-Cons


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## TnAndy (Sep 15, 2005)

You can't lay traditional block without a concrete footer....the wall will shift and crack.

They DO make a 'retainer wall' block that is sorta self locking ( each course steps back a 1/2" or so, and has a lip on the bottom that locks over the course below ). You fill with fine gravel when done. These are laid on a gravel base to start. No mortar is used on block.


But pouring a footer for convention block isn't rocket science. Get some 1x8 lumber, form both sides of a 16" wide footer, forming over the rock, and pour it. Small ones, like the one in my root cellar, I just mix Quickcrete by hand and pour.....I don't bother with a concrete truck.


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## fireweed farm (Dec 31, 2010)

You may also want to consider a good clear gravel/drain rock as the floor instead of slab.
Concrete may get slick/slimy depending on what you are doing in there.
I really enjoyed the drainage of the gravel.


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## Ziptie (May 16, 2013)

Good to know about the self locking.

"Get some 1x8 lumber, form both sides of a 16" wide footer"

But how do I hold the lumber up? I know usually you make some wooden stakes and drive them into the ground on the outside of the lumber, but can't really do that with bedrock. Ideas???


"They DO make a 'retainer wall' block that is sorta self locking ( each course steps back a 1/2" or so, and has a lip on the bottom that locks over the course below ). You fill with fine gravel when done. These are laid on a gravel base to start. No mortar is used on block."

Can I use this type of block on a free standing wall? I was going to leave some space between the north wall and the wall of the greenhouse.


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## jwal10 (Jun 5, 2010)

http://www.steel-dog.com/footing_brackets.html


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## jwal10 (Jun 5, 2010)

I would use the wall blocks to build the wall and then pour a concrete footing for the foundation. Best if bottom of the footing is below frost line so it doesn't heave. 12-18" wide. If you need to get back to, or above ground level, then you can go up with block. All of this needs to be level on top, all the way around. Then fill inside with gravel, makes a good heat sink (warms and holds heat at night) plus drainage.

If you want a wall on the south as part of the greenhouse (it would need to be the end, not side) you could use the blocks. Will need to be made so it is weather proof (harder because of the arch roof)....James


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## Ziptie (May 16, 2013)

Cool idea with the brackets

Hand an idea also. Could I take the 1X8..take a scrap pice of 2X4 set on edge across the 16 inch span of the brads and have the bottom flush with the bottom of the 1X8. Then move down a few feet and put the @X4 flat across the top of the 1X8s. Do I make sense? Could it work? Draw backs Hopefully this sad pic will show-up.


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## Swoop411 (May 29, 2012)

I know I am a bit late to this discussion, but I was just wondering why you didn't use some Tapcons to hold your forms to the rock? Then you just remove the Tapcons when your concrete has set and fill the holes left by the Tapcons with a concrete filler/sealer. Seems like the easiest solution to me.


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## Ziptie (May 16, 2013)

Well, never heard of those things before. Are they like concrete screws? Would I use are regular drill and drill them on the outside of the boards.Like I would a wooden stake. What would the spacing be on them?


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## Swoop411 (May 29, 2012)

Ziptie said:


> Well, never heard of those things before. Are they like concrete screws? Would I use are regular drill and drill them on the outside of the boards.Like I would a wooden stake. What would the spacing be on them?


I have used them in concrete, as well as block walls. I have also used a regular drill with a masonry bit, but a hammer drill would make the job go much faster. If you didn't want to buy a hammer drill you can rent them I believe. 

The only issue I have had is over-tightening the fastener and twisting the head off. If you fastened down some 2x4's and then secure your footer forms to these 2x4's wouldn't that work? After that you could lay your block wall and life is good!


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## chuckhole (Mar 2, 2006)

Attach a ledger board to the rock and then work off the ledger board.


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## Ziptie (May 16, 2013)

Thanks for the info. Can the ledger board be a 2x4 or does it have to be bigger? How long do you think the screws should be(I am assuming they come in different sizes)?


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## chuckhole (Mar 2, 2006)

Ziptie said:


> Thanks for the info. Can the ledger board be a 2x4 or does it have to be bigger? How long do you think the screws should be(I am assuming they come in different sizes)?


The ledger board is only for attaching your frame to the concrete. So the thicker the slab, the more pressure it will exert on your frame. There is no completely right answer. And the disappointing thing about concrete forms is that they are only temporary. More money and work for just a little use.

You definitely do not want to go any less than a 4" slab. You can use sand to level the site and fill in where required and sand is a lot cheaper than concrete. A water level is very handy when leveling out a site.

Personally, I would use at least a 2x8 for the ledger board and 2x6 for the form boards with 2x4's for the support boards. That is exactly what I am using for my greenhouse slab (15x20 slab for a 12x15 greenhouse). But I am able to drive the supports into the ground and do not have to use a ledger board.

The screws mentioned above hold quite well in masonry/concrete/rock. They are a double spiral. The outer spiral gets crushed as it is inserted and makes a friction hold similar to ring shank nails. As a general rule for fasteners (60/40 rule) you want 60% of the fastener length for holding power. So, countersink the fastener in the 1-1/2" thick wood about 1/4" and use a 3" screw. Does this make sense? Also, as mentioned above, a hammer drill is definitely the tool of choice for drilling the holes and driving the screws. If you can not borrow one, the Porter Cable 1/2" hammer drill is a good buy for the $60-$70. You can easily pay two to three times more. I have been quite happy with mine.

You probably would not need an anchor screw more than one every 2 feet. Depending on the contour of your rock, you have to do what is possible. For stability, I would use a single length ledger instead of two shorter ones per side.


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## Swoop411 (May 29, 2012)

Any update?


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## Ziptie (May 16, 2013)

Not yet, working on outside garden and fencing.:banana: Hopefully,Hopefully later this summer.


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