Learn About Spiral Staircase Foundations

Why Your Spiral Stair Foundation is Important

Before installing your spiral stair, or even choosing a place to install your spiral stair, one important factor to take under consideration to ensure the long-term stability of your stair is that of the foundation. While the foundation is not technically a spiral stair component, it is still very important to understand the ground directly underneath where your new staircase is going to go. If it’s the only place where your stair can go to suit your purpose, what steps can you take to ensure the ground is suitably solid if it isn’t already? And if there are steps to be taken to make it solid first, what steps can you take on your own and which will likely require a professional?

This is a series of questions you should go through when looking at where to place your stair, because you’ll want the chosen ground completely ready before the day the stair arrives. Otherwise your project will present much more of a headache than it needs to.

One way to figure this out easily is to break potential spiral stair location down by simple categories then figure out which have foundation issues and which don’t.

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.



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 stairsuch 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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