Cavity under concrete stairs

Question

I’m in the Ottawa/Gatineau area. At my home, there’s no concrete slab in front of the exterior stairs, which makes the first step from the ground to the stairs uncomfortably high.

I also noticed there’s a cavity beneath the stairs. From what I can tell, the stairs are poured concrete, and they only touch the ground near the wall of the house — the rest of the steps seem to be suspended, with a hollow space underneath.

I’ve started digging to pour a new raised concrete slab in front of the stairs to fix the step height issue. The slab won’t be attached to the house wall — it’s just meant to sit in front of the stairs. I’m preparing the base with about 3 inches of compacted gravel over soil before pouring the slab.

I have two questions before I continue:

1. Should I fill the cavity underneath the existing stairs with concrete, or is that hollow space there on purpose (for drainage or frost protection)?

2. Should I connect the new concrete slab to the existing stairs, or should I leave a small gap (expansion joint) between them?

Any advice or recommendations would be really appreciated!

Answer 1

You probably had something on each side before—probably soil. The stairs were built on gravel, and when you removed the soil, it allowed the gravel to spill out. There's no real good way to put gravel back, so likely the best you can do is fill with as stiff a grout as you can. If it slumps a bit at the outside faces, you can push up a wood board or something while it sets.

To add: no, you should not connect your new slab to the stairs. Install an expansion joint, whether fiber or elastomeric.

Answer 2

Its just possible that the steps may be ok. But most likely, they haven't been designed to be suspended.

Concrete is good with compression but not expansion. When you step on it, the top is under compression, but the bottom is stretching. Unless there is suitable reinforcing to take this stretch, concrete will break and crumble.

So it needs to be supported.

Answer 3

It is unfinished. Consider building a form to add the last step. In the process, fill the cavity.