Learning Center · Diagnosis
Why Is My Porch Pulling Away From the House?
WHAT A PORCH GAP USUALLY MEANS
| What you see | What moved | Usual fix |
|---|---|---|
| Gap wider at the top, porch tilting away | The porch slab rotated on its own | Seal, regrade, or replace the porch |
| Gap about even from top to bottom | The porch dropped as one piece | Seal, or lift on settled soil |
| Porch now slopes toward the house | The porch settled on the wall side | Replace or support, then seal |
| Porch roof cracking at the columns | The slab under a column dropped | Piers under the columns |
| Cracks inside near the entry too | The house corner may have dropped | Floor elevation survey |
Why is my porch pulling away from the house? Most of the time the porch is a separate piece of concrete, sitting on shallower and looser soil than the house, and it settled or tilted on its own. That is why the gap opens right at the wall, and why a sinking porch so often leaves the house above it untouched. Sometimes it goes the other way, and the corner of the house beside the porch is the part that dropped. Look at the doors, drywall and brick near the entry before you decide, and keep water out of the gap in the meantime, because the joint between a porch and the house is a direct path to the foundation.
Why porches move separately from the house
A slab house stands on beams that run around its edge and under its load-bearing walls. A front porch is usually built differently. It is often poured as its own slab, sometimes after the house, with a thinner edge than the house beams. It sits on the soil right beside the house, which on most lots is ground that was dug and backfilled when the beams went in, and backfill is rarely as firm as soil that was never disturbed. Some builders tie the porch to the house with steel bars, and some simply pour it against the beam.
Then the weather works on it. The porch edge sits at the roof's drip line, where storm water lands, and downspouts often empty right at the porch columns. Our clay swells when it soaks and shrinks hard in a drought, and the soil under a porch goes through every one of those swings with very little weight on top to hold it down. A porch that is not tied to the house drops and rotates away from the wall. A porch that is tied in cracks at the joint or pulls the steel loose. A masonry chimney on its own pad does the same thing, which we explain in chimney pulling away from the house.
Entry steps, back patios and carport slabs follow the same rules. Each one is a small slab with little weight on it, sitting in the wettest and driest strip of soil on the lot, so each one tends to drop and tip away from the house before anything else does. A back patio that has tilted toward the house is worth the same attention as a front porch, because it drains toward the same beam.
Is it the porch or the house?
Start at the joint. A gap that is wider at the top than at the bottom means the porch has rotated away from the house. A gap that is about the same from top to bottom means the porch dropped as one piece. Then lay a level across the porch, pointing away from the wall. A porch should fall away from the house so rain runs off it. The code San Antonio adopted, in section R401.3 of the residential code, asks for paved surfaces within 10 feet of the house to slope at least 2 percent away from it, about a quarter inch per foot. A porch that now tilts back toward the wall sends every storm into the joint.
Then check the house. Walk in the front door and look for a door that started sticking, diagonal drywall cracks over the door and nearby windows, and a floor that runs downhill toward the entry. Outside, look for stair-step cracks in the brick above and beside the porch, and look up at the porch roof. Where columns hold up a porch roof, a sinking porch takes the columns down with it, and the beam they carry cracks at the corners or pulls away from the house.
If the house is quiet and only the porch moved, you have a porch problem. If the cracks inside cluster at the same corner, the house corner may have dropped too, and the porch is only the most visible part of it. Stair-step brick cracks above the porch are the sign that most often settles which one it is.
Then put a date on it. Make a pencil mark at the top and the bottom of the gap, write the date beside each mark, and photograph both with a tape measure in the frame. Look again after a dry month and again after a good rain. A gap that holds its width through both is old movement, and it only needs sealing. A gap that opens a little every dry spell is still moving, and sealing it now just means sealing it again next year. A gap that has grown noticeably in a few weeks, or a porch roof beam that has started to sag between its columns, should be looked at within days rather than seasons, and keep people out from under a porch roof that is moving.
Why the gap matters even when the house is fine
A porch gap is a funnel. Rain running off the porch drops straight down the joint to the bottom of the house beam and soaks the clay there, the one spot you most want to keep evenly moist. Over time that water can carry soil out from under the porch and the beam alike. An open joint also gives termites a hidden path to the wood framing, and a porch that dropped at the step becomes a trip hazard.
The Foundation Performance Association's owner's guide covers both halves of this. It asks for flatwork within 10 feet of the house to drain away at about 2 inches of drop per 8 feet, on a compacted base rather than sand, and for the joints between flatwork and the foundation to be sealed so water cannot get down beside the slab edge.
How a porch pulling away gets fixed
The right fix depends on what moved and whether it is still moving.
Seal the joint. If the porch moved years ago and has stopped, a foam backer rod pushed into the gap and a flexible sealant over it keep water out of the joint. That is honest weekend work. Do it after you know the gap has stopped growing, or it tears again with the next dry spell.
Fix the water. Move downspouts off the porch columns and out at least six feet, and get the soil around the porch sloping away. The Foundation Performance Association's maintenance and inspection guide asks for downspout water to be carried five to ten feet from the building before it reaches the soil, and for paving near the house to drain away from it. A porch that keeps getting soaked will keep moving, whatever else is done to it. How far downspouts should drain has the details.
Lift it. Mudjacking and foam injection pump material under a sunken slab to float it back up. They can work on a porch whose soil has finished moving, and they disappoint on clay that is still swelling and shrinking, because the new material rides the same soil. We do not sell either one, and concrete leveling in San Antonio explains how to tell which kind of ground you have.
Replace it. A porch that is cracked through, pitched toward the house, or sitting on a bad base gets torn out and poured again, on a compacted base with steel in it, with thickened edges and a slope that drains away from the house. That is concrete flatwork, and it is work we do.
Support it. When the porch carries a roof, or when the house corner beside it dropped as well, the answer is piers. We press steel or hybrid piers down to load-bearing ground under the porch columns or the house beam, then lift in measured stages. The piers carry a lifetime transferable warranty, and we come back every year for a performance follow-up inspection.
A wood porch on posts is its own case. The posts usually stand on concrete blocks or small footings that settle, and the wood at the bottom of each post rots where it holds water. The fix is new footings, new posts or shims, the same kind of work as pier and beam foundation repair.
What we look at on a porch call
The free inspection measures both pieces. We take elevations on the porch and across the floors inside with a ZipLevel altimeter, read to a tenth of an inch, so the map shows whether the porch dropped alone or the house went with it. We measure the gap, check the slope of the porch, look at the columns and the porch roof, and walk the drainage around the entry. About a third of our inspections end with no repair needed, and an old porch gap that stopped moving years ago often lands there, with a note to seal it.
When a single corner of the house turns out to be the part that dropped, what a sinking corner usually means walks through that repair. The inspection is free in Bexar, Travis, Williamson, Hays, Comal, Guadalupe, Kendall, Medina, Bastrop and Caldwell counties. Book it below or call (210) 816-0034.
