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Design Phase Question- Concrete Pad

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I am planning on building a small outdoor island next to an existing patio (8-10'). I need to do a concrete slab for the base. How deep should the concrete be, keep in mind I live in MA where freezing temps are common during the winter?

 

 

Eric

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All slabs should be 3-4" or greater and have rebar or steel mesh. You might consider and inch or two of sand underneath to help. There may be others here with more experience in freezing temperatures. I live in So Cal. I also use a high ksi rated mix. None of my concrete projects have ever cracked.

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This pad would probably be considered an extension of the existing patio. What you really need to do is go to your county's web site and mouse around until you find engineering and building code info. They will tell you exactly what you need.

 

It will probably be a minimum of 4" thick reinforced concrete on a minimum of 4" of compacted stone. Sand does not compact well and can wash out quickly if you have flooding issues. They will specify some compressive strength around 3500 psi and some air entrainment level around 6%.

 

You also want to think about water run off from the existing patio since you are kinda building a dam on one side of it.

 

While you are looking at the county code info also check out the requirements for exterior / underground electric runs, grounding, plumbing, and drains if you plan on adding power and water.

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There you go. Bubba makes a good point, if your island is not on pads/feet to allow air and water to flow under it, make sure you allow for runoff. I prefer to cover the bottom of my islands and use 4x4" Trex pads as feet to allow airflow. This prevents mold, mildew and electrolysis which will happen if you attach directly to the slab.

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