Why attachments move separately
A masonry chimney, a front porch, a concrete stoop or a later addition often has its own footing, separate from the main foundation. A masonry chimney is especially heavy for its footprint: its full weight rests on a relatively small pad or footing. If that footing was shallow, undersized or placed on poor soil, it can settle or tilt while the house stays put. The same is true for porches and stoops, which were often built with shallower footings than the house, sometimes on backfill that was never compacted.
Common causes
- Undersized or shallow footings that cannot carry the weight or sit above the frost line
- Loose backfill placed against the foundation after construction, which settles for years
- Water from a downspout or poor grading softening the soil under the attachment
- Expansive clay that shrinks and swells under a small, lightly loaded footing
- Frost heave lifting a porch or stoop in winter; see frost heave and foundations
- Tree roots drying soil next to the attachment; see tree roots and foundations
- Deteriorated connections, such as rotted ledger boards on porches
How serious is the gap?
A small, stable gap that has not changed in years may only need sealing and monitoring. Warning signs that call for a prompt evaluation include:
- A gap that is widening, or is wider at the top than the bottom (the chimney is leaning outward)
- Cracks in the chimney masonry or loose bricks
- Gaps at the roof line where flashing has pulled away and water gets in
- A fireplace hearth or firebox separating from the chimney, or gaps inside the firebox
- Porch roofs sagging or porch posts leaning
- Stoops that slope toward the house, sending water to the foundation
A leaning chimney is a safety hazard: masonry can fall, and gaps can let heat and gases reach combustible framing. Stop using the fireplace until a chimney professional has checked it.
Repair options for chimneys
- Evaluation: a foundation contractor or engineer checks the footing and whether the chimney is still moving; a chimney professional checks the flue and firebox.
- Underpinning the chimney footing with helical or push piers and a steel bracket, then lifting the chimney back toward plumb where possible.
- Rebuilding the chimney above the roof or entirely if it is badly damaged.
- Resealing and reflashing once movement has stopped.
Repair options for porches, stoops and additions
- Helical piers under porch beams or addition footings, installed with small equipment and loaded right away
- New footings below frost depth for porch posts and steps
- Slab lifting with polyurethane foam or grout for concrete stoops and porch slabs; see mudjacking vs. polyjacking
- Replacing a stoop that is cracked through or badly out of level
- Reattaching porches with properly flashed and fastened ledgers where the connection has failed
Is it the attachment or the house?
If the gap opened because the attachment dropped, you usually see the attachment tilted away from the house, with the house itself level near the connection. If the house has settled, you may see cracks inside, doors sticking and sloping floors near the connection too. An elevation survey across the house and the attachment answers the question. See foundation engineer reports explained.
What it costs
Costs vary by the attachment and access. Slab lifting for a stoop is often among the least expensive foundation repairs, while underpinning a chimney with piers usually costs more than a single pier under the house because of brackets and lifting. National cost guides put individual piers at about $1,000 to $3,000; see the cost guide.
Preventing separation
- Keep downspouts away from chimneys, porches and stoops.
- Seal the joint between a stoop and the house so water does not run down along the foundation.
- Keep soil and mulch sloping away, not piled against the attachment.
- When building an addition or porch, confirm footing depth and size on the permit plans.
How to monitor a gap
Before calling, it helps to know whether the gap is still moving. Measure it at the top and the bottom with a tape and write down the date, or place a crack gauge across it. Take photos from the same spot. Repeat every month or two, and after heavy rain or a hard freeze. A gap that is the same size after a year is usually less urgent than one that grows each season. Keep the measurements; a contractor or engineer will find them useful.
What contractors look at
- The size and depth of the footing under the chimney or porch, often by digging a small test hole
- Soil type and moisture next to the footing
- Downspouts, grading and any water that flows toward the attachment
- Whether the attachment is tied to the house framing, and how
- Signs of movement in the main house near the connection
Additions and garages
The same principle applies to room additions, sunrooms and attached garages built after the main house. They usually sit on their own footings, sometimes shallower or on less compacted soil, and the joint between old and new is where cracks appear first. A crack running along the line where the addition meets the house, or a floor step at that line, points to differential movement between the two foundations. Repairs follow the same pattern: support the moving part with piers or new footings and fix drainage.
Porches on older homes
Many older homes have wood porches on brick or stone piers, or on posts set directly on the ground. Over decades, piers settle, posts rot and the porch roof starts to sag. Rebuilding the piers on proper footings below frost depth and replacing damaged posts and beams often restores a porch without replacing it. If the porch roof is tied into the main roof, have the connection checked as part of the repair.