Indoor Foundations

If your spiral stair will be indoors then it’s highly unlikely that you’ll have to make any adjustments to your floor space before installing your spiral stair.

One location where you may consider making adjustments is if your stair will be on a concrete floor in the basement.

The concrete will be more than stable enough. But it may have some cracks or crumbling in it due to age and maybe even water flow through some storm doors and across the slope of the floor toward the sub pump. Especially if it’s an older house with an unfinished basement.

If this is the case then taking the time to fill these cracks with a quick concrete mix and trowel job should be sufficient. Let the concrete repairs cure then install as planned.

Outdoor Foundations

If you’re spiral stair is going to be outside then there are a lot more dynamics to consider. Will this stair be on a deck, patio, driveway, or just a concrete pad? Or is there any type of finished floor at all where you plan to install the stair? Each of these will have different factors to check before knowing the stair will be secured.


Different Foundation Types

Learn about each of these locations and how their foundations work

Aluminum Powder Coated White Spiral Staircase with Treads


If you’re mounting a spiral stair directly to your deck then you’re likely safe. Especially if the deck is of newer construction. If you’ll be installing a heavier outdoor stair such as a galvanized steel stair instead of an aluminum stair, then it might be prudent to install extra support into your joist system beneath the floor boards just under where you’re putting the spiral stair.


If your driveway is blacktop, concrete, or any other hard surface with a sufficient depth to it, then your surface is stable enough for installation. Just check how long the bolts for your base plate mount will be so you know you have a thick enough surface to work with. Just keep in mind the same principle as with the basement concrete floor.


The same principle applies to patios. If it’s made from pavers that haven’t been mortared together then you’ll need to first install a footer. You may need to teach yourself/lookup how the cut a circle into your current pavers so you don’t have to lay new ones down and so you don’t interrupt the flow/pattern of your pavers. Once you’re circle is cut, you have space to pour your footer.

Concrete Pad

A monolithic pour concrete pad is just like any other; make sure it’s in good shape prior installing a heavy spiral stair atop it. Repair cracks and crumbling. And make sure it’s of a sufficient thickness before bolting your stair base into it.


One issue that immediately makes for a precarious foundation is any kind of slope. Whether it’s how your land lays or if your concrete pad is sinking on one side. If you have a problem with the ground sinking where you’d like to pour a concrete pad then you need to do some direct filling prior to pouring a pad.


One of the simplest, non-invasive things to do in your yard to create a workable platform for your spiral stair is to install a concrete footer. This is essentially just a concrete tube that goes below your ground a little deeper than your local frost line. This is a common foundation for deck posts.

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