Will my coop sink? (New to this)

[merryberry]

Hi all!
I am new to the world of chickens, and new to building as well. DH and I are just about to start building the coop/run, and a friend has put some doubt into our minds about the foundation we had planned.

We purchased the Garden Coop plans (www.thegardencoop.com) and based our design off of it. We are planning on a 10'x10' structure that will look something like this (**just look at this for the basic framing, as it is NOT a complete sketch-up of our plan. The roof will be corrugated panels, probably the metal ones, and on a slope, not flat like it looks in the pic. And the door isn't framed in in this pic either. There will also be hardware cloth, roosts, and door/access to the coops, etc that isn't shown).

So our plan is to raise this slightly up off the ground using 8"x8"x18" concrete blocks that are set into the ground with about 3" sticking up (as described in the Garden Coop plans that we purchased). We are going to put a block at each corner and under each stud, for a total of 12 blocks. Our plan is to used crushed gravel at the bottom of each hole to level the blocks.

Our friend said that the coop will sink if we don't dig 36 inches down and fill the holes with concrete or crushed limestone/gravel??? He also said that the entire weight of the coop would be bearing down on each block, which confused me. I thought that the weight would be distributed among all the blocks. He has construction experience, so now I am worried about our plans. On the other hand, I've seen plenty of coops on the member pages like what we had planned that don't appear to be sinking...

Any thoughts or experience would be appreciated!

 

[mikecnorthwest]

The weight will be evenly distributed amongst the 12 blocks. I don't understand why he would want you to dig 3' and fill with cement. I'm assuming that the ground your building on is already compacted and not fresh fill? If you look at my BYC page you'll see that my coop sits on pressure treated 2x4's which are simply laid on the ground. In my opinion, as long as you're putting this on solid ground, you should be fine. Frankly I can't begin to imagine 12 concrete blocks sinking into the ground.

 

[merryberry]

Thank you!

Yes, the ground is already compacted. Even though we've had a ton of rain lately, it is still very solid (I've been checking everyday!)

 

[Ridgerunner]

Welcometo the forum.

Glad you are here.

I'm only goong to address yout specific question, and my answer is, it depends. How much, if any, the structure sinks depends on your soils type and your weather. If you have a clayey type soil, it will probably settle, especially if it gets wet a bunch. If it stays dry all the time, you might be OK. If it is a contained sand, it will probably do fine. A contained sand is one that is trapped and cannot be pushed or eroded away. Sand on a beach, on top of a rise, or where it can wash away does not meet the condition of being contained. I spent my career as a structural engineer and we were always glad to find a contained sand for our foundations. Since your friend is in the construction business in your area, he probably is aware of the local conditions and probably knows what he is talking about. 36" of gravel or concrete seems severe but I am not familiar with your conditions.

If you get it level and don't have differential settlement, you will get load distribution to all blocks. The blocks under the coop portion will see more load than the ones holding up only the run framing and fencing. The blocks on the downwind side will see more load due to the wind. The entire structure will distort to help equalize the load, but, yes, some blocks will see more load than others.

Have you asked your friend what else he might suggest? I don't know your soils conditions, but with your specific design, I'd consider geting treated 4"x6" timbers and putting them all the way around as a foundation. It would make it easier to predator proof the coop and run.

Good luck!!!

 

[merryberry]

Quote:
Thanks for the welcome and your input

.

When you suggest the 4x6 timbers, do you mean in place of the concrete blocks, or sitting on top of the blocks? The ground isn't completely level (it slopes downhill a bit), so I'm not sure how 4x6 timbers by themselves would work for getting the structure level, if you mean that we should use them as the only foundation?

Our plan for predator-proofing is to wrap the entire thing in hardware cloth, including burying it about 12' into the ground. Any suggestions on that front (or any other) would be appreciated as well, if you have them!

 

[Ridgerunner]

I was thinking instead of the blocks. Screwing that down to the 4x6's would make that very stable in a high wind. If it is not level, that does change it a bit. Each location is different and takes different solutions.

Burying the hardware cloth will work. Depending on your soils conditions, it may be a lot of physical labor or may be fairly easy. Of course, if it is easy for you it will be easy for a coyote, fox or raccoon. My soil was extemely rocky, so I used something like this.

Alberta Aprons
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex916

 

[Hangin Wit My Peeps]

My 8x8 coop which is really heavy and built like a house is on six concreat blocks and has not sunk at all. I think you will be ok.

 

[patandchickens]

I have noticed an alarming tendency for people who work in "the" construction industry in one capacity to consider themselves automatic experts on ALL aspects of construction. T'aint necessarily so

Yes, unless you have uneven settling, each of your blocks will carry only a fraction of the weight of the coop (for instance if there are 4 blocks and the weight is evenly distributed, a 1000-lb coop will be applying 250 lbs of weight on each individual block). Also that weight will be distributed over however many square inches the footprint of the block is.

I would not suggest using 12 blocks however. The chances of uneven settling become Very Large with that many blocks, and if your soil is somewhat unhomogeneous (has soft spots, or buried rocks, or whatever) you can get uneven settling to the point that it starts to damage your coop - stressing or cracking your sills/joists, tearing wall joints apart, etc. Better to use only 4 or 6 blocks, if at all possible.

If you have a very solid homogeneous soil, you should be ok with just putting the blocks (when placing the blocks directly on the ground (or you can set the blocks on a larger paver (not too large, you don't want it to crack) which will further help spread the load). Remember you will have to get the blocks' tops *exactly level* with each other. If you are a little unsure about settling, you can dig down six inches or a foot, fill it with gravel or screenings and tamp it very firmly and thoroughly, and *then* put your blocks on, for a little extra margin of error.

Good luck, have fun,

Pat

 

[Bossroo]

Your friend may have experience with frost heave for your area, therefore he may be giving you good advice. Instead of settling , a corner or two may be rising out of the ground. Ask him !

 

[merryberry]

Quote:
Well the frost issue does make sense for our area (northeast ohio) because the ground freezes, but he was emphatic about the entire weight of the coop pressing down on each post and causing the coop to sink into the ground...nothing about it rising up. And honestly, I don't want to bring up the question to him again because the discussion caused some tension (unnecessarily I know, but it did).

So given that, would it rise up because the ground freezing would squeeze the blocks out of the ground? If so, how can I prevent it? I'd follow the advice from ridgerunner about the 4x6's but the ground isn't level. This isn't something I know anything about so your thoughts are welcome!