Looking for a solution to hold sill beam and posts in place...

[kreyszig]

Hi,

so I have this chicken coop project I have mentioned in a previous post that I am working on (8' x 40' with the covered run that will host solar panels in the future), that will be using 4x4 posts and pressure treated 4x4 sill beams. I am looking for the most cost/time effective solution to hold the posts and sill beams in place that will not compromise long term stability.

The coop will be located in a back field on my lot that has a shallow ground (about 2.5-3') and which is mostly brown clay over the bedrock. I am located in eastern Ontario, so the temperature can go under -20F in the winter and the frost line most probably goes down to the bedrock level in that location. The dirt being mostly clay, it shifts quite a bit from one year to another with the seasons and the rain. The ground can be pretty wet as well since the flat shallow ground does not provide much drainage.

Initially I was thinking of digging a trench down to the bed rock, fill it with big rocks, then sand and/or gravel. I would then make forms, have a foundation (no footing, no slab) about 8" wide by 16" high all around the coop poured and anchor the sill beams to it. I assume this would be a good stable solution, but it might be overkill and not the most cost/time effective.

Another idea I have is to dig a hole down to the bedrock at each post location, then use sonotubes to pour concrete pillars. I could potentially mix the concrete myself for this, and I could use one of the widely available u-shaped galvanized steel brackets to hold the sill beams. The pillars would reach slightly higher than the existing grade. I would add a layer of compacted stone dust to bring the grade up and I would have the sill beams rest on the pillars + stone dust. What I am not sure about with this solution is what will happen when the ground freezes. Will it make the pillars shift over time? Will there be issues when the ground freezes between the pillars and push the sill beams up? Should I add footing to the pillars and/or somehow anchor them to the bedrock?

Input would be very appreciated. Also let me know if you can think of a better solution.

Thanks!!

[Don P]

Leave the sill several inches above finish grade. Run the chicken wire to grade and use landscape staples to pin it down. If the ground moves it can flex. I've also seen people rip a V point on the bottom edge of a skirt board that extends below framing down to ground in the hopes that it would split the heave rather than lifting. Just a thought, if something like that was relatively lightly attached to the face of a raised sill with enough nails or screws to keep it in place but few enough that they would shear before moving the structure.

For a habitable building you would drill into the bedrock and epoxy rebar that extends up into the pier... but this is a chicken house.

[kreyszig]

Thanks Don,

Maybe I could use some kind of skirt board as you suggested mounted with lag bolts to the sill beam and have slotted holes on the boards so they can float with the ground. I want to bury a predator apron outside the coop. I could staple it to the floating skirt board.

Another option with the piers solution would be to remove all the clay under the seal beams and replace it with rocks, gravel and/or sand. I have a good amount of rocks on the side of the fields on my property that could use for this purpose. However they have been there for 40+ years and some bush trees have grown through them, so it might not be easy to get to them.

What kind of epoxy is used to attach rebar to bedrock? Would you use concrete drill bits with a hammer drill to make the holes?

[Don P]

This is one that should be readily available from a quick google, there's a million brands, technically look for a building code approval or astm reference when you are building something.
https://www.lowes.com/pd/Red-Head-Anchoring-Adhesive-Actual-Net-Contents-9-5-fl-oz/1000207843

Your shield bedrock is going to frustrate a hammer drill. You can probably rent a percussion drill, which is just the next stage up of harder hitting big honkin hammer drill. Mine is one of the Hilti's that many rental shops use and it will drill into your bedrock. This is still a drill, you don't want an electric jackhammer. There is a hammer only mode on these though, if you get it with a clay spade it may help with the excavation, that works nice in that stuff that is somewhere between rock and dirt.

Rent a skidsteer with bucket and forks to recover your rock piles, you'll move more in a day than you would by hand in a month.

3 widely spaced rebars with adequate concrete cover is the minimum number of pins to stabilize a pier. If you can tie, weld or hook the rebar to the upper bracket you then have a "continuous load path". Next time you're in a parking lot look at the size sonotube pier they use to hold up a light.

You can't have frost heave without water, if it drains well it doesn't heave. Chickens fail to respect any of our plans with regard to drainage.