01 May 2015

Engineering the front steps

My house is load-bearing masonry. That means that the bricks on the outside of my house are not purely decorative; they actually hold the house up. Similarly, our porch foundation is solid brick. Brick is great in compression, but its shear and tensile strength are practically nonexistent. As a result, attaching stairs to the brick porch foundation is prohibited by code. So I had to figure out the best way to build these stairs and make them safe and secure.

The solution is to build them completely freestanding. Freestanding structures have a different set of rules than ones attached to permanent structures. If I had been able to attach a ledger board to the house (as is typically done with wood-frame buildings), the footings would have to be buried below the frost line, which is about 30" here. This is to prevent frost heave - the movement that occurs when moisture within the soil freezes in cold weather (ice expands as it freezes, displacing the soil around it and forcing it up). Below the frost line, the water within the soil does not freeze, so footings at this depth are safe from that displacement. Frost heave could easily shear the bolts and damage the brick or the ledger board, which is why it is so important for attached decks and stairs to have footings below the frost line.

But because these stairs will be freestanding, they only have to be set on undisturbed (for 5 years) soil. The reason for the difference is that if the staircase suffers from frost heave, the stairs will move as a unit, independently of the house, damaging neither structure. The rise on the final step might change slightly, but not significantly enough to cause problems. That's the reason I only dug about 8" down, tamped down, then filled with gravel and sand before setting solid concrete block. Once I had the foundation figured out, the rest of the construction just fell into place. I'll leave that for the time I actually have pictures as a visual aid.

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