How Deep Do Porch Footings Need to Be?

What Footing Depth Does a Porch Need?

A roofed porch attached to the house needs footings at least 12 inches below undisturbed ground and below the frost line, like the house itself. An open porch built like a deck follows the deck rules in R507.3. Steps and landings depend on your local code.

The question is whether the porch is a building or a deck. A roof makes it part of the structure and ties it to the house’s foundation rules. Look up your frost line depth for the number your code sets.

Do You Need a Footing for a Porch?

You almost always need footings for a porch, and the question is how deep. A porch with a roof carries the roof’s weight and snow load, so its posts need footings sized for that load, at least 12 inches deep. An open porch needs footings unless it meets the small free-standing deck exceptions.

Those exceptions are narrow: joists on grade, or a deck of 200 square feet or less on pier blocks with a low walking surface. A roofed porch with posts does not qualify. See deck footing depth for the sizing table.

Do Porch Steps, Stoops and Landings Need Frost Footings?

Steps, stoops and landings often need frost footings, and the rule is local. Wisconsin’s Uniform Dwelling Code, for example, includes footings for landings and stoops in its 48-inch minimum frost depth. The IBC requires frost protection at required exit landings with outward-swinging doors.

The IBC’s wording limits it to what is needed for the door to open freely: section 1809.5.1 asks for frost protection at exterior landings “to the extent necessary” to ensure the unobstructed opening of required exit doors. A stoop that heaves can jam a door, which is why codes pay attention.

Ask your department whether your steps need a footing, and how deep, and have the answer written on your permit drawing.

How Are Porch Roof Posts Supported?

Porch roof posts are supported by concrete footings sized for the roof load, with a post base that anchors them against wind uplift. A footing sized for a deck’s 40 psf load may not be enough for a roof, so use the porch’s plans or an engineer’s numbers.

The footing must reach at least 12 inches below undisturbed ground, and below the frost line where your code requires it. Posts that rest on a slab need anchors suited to the slab, and an inspector can tell you if the slab is thick enough.

Why Do Porches Pull Away From Houses?

Porches pull away from houses when the porch footings and the house foundation move by different amounts. A house foundation below the frost line stays put. A porch on shallow footings rises and settles with the frost, so a gap opens between them.

The fix is to match the porch footing depth to the house. Frost heave explains the mechanism behind that movement.