⚠️ Significant Slope, Separation From the House, or Any Structural Instability — Restrict Access Now
A porch or deck that has settled significantly, is separating from the house, has posts that are visibly tilted or have soft bases, or that feels unstable underfoot should have access restricted immediately — especially while people are on it or during high-use periods like gatherings. Ledger failure in particular can produce sudden partial collapse with no further warning. Do not attempt to shim, jack, or temporarily brace a settling structure. Contact a licensed contractor or structural specialist for evaluation.
📍 Quick Summary
- One post dropping: localized footing failure or post rot at that specific support — fix that support
- All posts dropping uniformly: general soil bearing failure beneath the structure — drainage and soil evaluation needed
- Lifts in winter, settles in spring: frost heave — footings are above the frost line
- Gap forming between deck and house wall: ledger board issue — most dangerous pattern, restrict access and call a contractor
- Post rot at or below grade is the most overlooked cause — probe every post base before attributing movement to footing or soil
Settlement Pattern Decoder
Before inspecting anything else, identify the settlement pattern. Where and how the structure is dropping narrows the cause significantly before any hands-on inspection.
▼ One Corner or Post Drops
Localized footing failure or post rot
One support drops while others remain stable. Most likely cause: the footing at that post is inadequate (undersized, shallow, uncompacted soil below it), the post itself has rotted at grade level and is compressing, or the soil beneath that specific footing has been eroded or saturated by a concentrated water source — often a downspout or roof runoff path nearby.
▼ All Posts Drop Uniformly
General soil bearing failure
Structure sinks consistently across all supports. More likely a general soil bearing issue — poorly compacted fill under the entire footprint, repeated saturation from drainage failure affecting all footings equally, or original footings that were all undersized for the soil bearing capacity. Also common when the porch or deck was built on the same disturbed backfill as the house excavation.
↑ Lifts in Winter, Returns in Spring
Frost heave — footings above frost line
The structure lifts during freeze and settles during thaw. Classic frost heave signature. Footings poured above the regional frost depth are susceptible. The heave is typically reversible, but each lift-and-settle cycle widens any cracks in piers, loosens post connections, and gradually worsens misalignment with the house attachment.
↗ Gap at House Wall Connection
Ledger board failure — most dangerous
A gap forming between the deck or porch framing and the house wall indicates ledger board movement. The ledger bears the full weight of the structure's house-side beam — if it fails or detaches, that half of the structure drops suddenly. Any visible gap, movement, or flexing at the ledger attachment warrants immediate professional evaluation and structure access restriction.
6 Causes of Porch and Deck Settlement
01
Ledger Board Failure — Highest Safety Risk
The ledger board is the horizontal framing member bolted to the house rim joist that supports the deck or porch on the house side. Ledger failures cause more deck collapses than any other single cause because: the ledger bears a significant portion of the structure's total load; it is often installed through flashing into the band joist where moisture can collect and cause concealed rot; improper fastening (nails instead of bolts, or insufficient fastener pattern) creates progressive separation under live loads; and the failure can be sudden and complete rather than gradual. A gap forming between the deck frame and the house is the most visible warning sign.
Signs: visible gap at house wall; deck surface tilting away from house; fasteners pulling through; flashing failure or water staining at the ledger location. Restrict access and call a contractor immediately.
02
Shallow or Undersized Footings
Post footings for porches and decks are often poured too shallow — either above the frost depth (leading to heave), or on inadequately compacted backfill from the original house excavation. Concrete tube forms ("Sonotubes") poured directly into disturbed backfill without reaching undisturbed soil or frost depth provide minimal long-term resistance to both settlement and heave. Undersized footings — too small in diameter for the load and soil bearing capacity — slowly punch through soft soil over years.
Signs: settlement appears within the first few years of construction; frost heave occurs seasonally; posts rotate or tip rather than drop vertically; footings visible above grade may show cracking or displacement.
03
Post Rot at Grade Level
The base of a wood post at or below grade is the most vulnerable point in any exterior structure. Soil contact, debris accumulation, and post bases that don't drain hold moisture against the wood continuously. Pressure-treated lumber rated for ground contact (UC4B or higher) resists rot, but posts that were not properly rated, were installed without base hardware keeping wood off concrete, or whose treatment has degraded, develop rot at the base while appearing sound above grade. As the post base softens, it compresses under load and the structure drops at that support.
Probe the base of every post with a screwdriver or awl — push firmly at the lowest 6 inches. Sound wood resists firmly; rotted wood allows penetration or sponges inward. Soft post bases at grade = cause identified.
04
Soil Erosion From Roof Runoff or Poor Drainage
Roof runoff that is not captured by gutters falls directly at the drip line and often directly onto the footprint of an attached porch or deck. Over years, this concentrated water erodes the fine-grained soil from beneath and around footings, reducing their bearing area and eventually undermining them. Visible indicators include soil scouring or channeling near post locations, exposed aggregate or void spaces around footings, and settlement that correlates with rain events or follows a particularly wet season.
Check whether gutters discharge at or near deck post locations; look for erosion channels or exposed footing bases; note whether movement worsened after a heavy rain season.
05
Frost Heave of Shallow Footings
In cold climates, footings poured above the regional frost depth are lifted by frost heave each winter and settle back each spring. Isolated footings — single posts, not a continuous foundation wall — are particularly vulnerable because each footing is an independent bearing point that can heave or drop independently. When different posts heave by different amounts, the structure racks and stresses its connections. Repeated frost cycles loosen post base hardware, widen cracks in piers, and gradually distort the framing. The fix is footings drilled below the frost line — helical piers are often used for existing structures.
Distinctive seasonal signature: structure lifts noticeably in winter and returns in spring; different posts heave by different amounts; stair alignment changes seasonally; condition has worsened gradually over years of frost cycling.
06
Termite or Carpenter Ant Damage to Structural Members
Subterranean termites travel from soil into wood through mud tubes or direct contact with soil, and exterior structures are among the most accessible targets. Carpenter ants excavate galleries in moist or partially rotted wood for nesting. Both types of damage hollow out structural members — posts, beams, and joists — while leaving an exterior shell that appears intact. The damage is load-path specific: when a post or beam loses structural capacity from insect damage, the load redistributes to adjacent members, potentially overloading them. Settlement from pest damage looks like structural loading failure and requires pest inspection alongside structural evaluation.
Mud tubes on foundation or post bases = subterranean termites. Fine sawdust-like frass at post bases = carpenter ants. Hollow-sounding structural members when tapped. Settlement without obvious footing, rot, or drainage cause.
How to Inspect Your Posts
Post Inspection Checklist — Do This Before Any Other Diagnosis
Probe the base with a screwdriver or awl. Push firmly at the lowest 6 inches of each post. Resistance = sound wood. Penetration without force = rot present. This single test identifies the most common cause of porch and deck settlement.
Check plumb with a level. Each post should be plumb (vertical) in both directions. A post tilted inward or outward has either rotated from its footing or the footing has shifted. Note the direction of tilt — it indicates the direction the base has moved.
Inspect post base hardware. Post bases that are properly installed keep the wood off the concrete and allow drainage. Posts with direct wood-to-concrete contact or without post base hardware almost always show rot at the base. Check whether hardware is still properly attached or has pulled away from the footing.
Look for mud tubes. Subterranean termite mud tubes — tan or brown tunnels roughly the diameter of a pencil — on the post base, the footing, or the concrete slab indicate active termite activity. Call a pest inspector before proceeding with any structural repair.
Check drainage around footings. Is soil graded away from footings? Are there erosion channels near any post? Is a gutter downspout discharging anywhere near post locations? Water concentration near specific posts explains differential settlement.
Inspect the ledger connection from inside if possible. From the basement, crawlspace, or interior, look at the rim joist where the ledger is attached. Water staining, rot, or rust at bolt locations indicates ledger moisture damage — a serious safety concern regardless of whether exterior movement is visible yet.
Why You Should Not Temporarily Shim or Jack a Settling Structure
The instinct to place a temporary shim or jack post under a settling deck corner before a professional can evaluate it is understandable but potentially dangerous. Temporary support that is improperly positioned, undersized, or placed on inadequate bearing can shift load to already-compromised members, overstress adjacent connections, or create an unstable condition that fails suddenly when the structure is loaded. More importantly, temporary support doesn't address the soil, footing, or rot condition causing the settlement — the structure remains unsafe even with temporary support in place. If the structure is significantly settled or unstable, restrict access rather than attempt temporary support.
Severity Classification
C.M.
From the Expert
"When I'm called for a settling porch or deck, the first thing I do is pick up a screwdriver and probe every post base. I've found 80% of porch settlement diagnoses resolved at that step — the post is rotted at grade and the structure has been slowly compressing into the decayed wood. The footing is fine, the soil is fine, the post above grade looks perfectly sound. But the bottom 6 inches of that post have the structural integrity of wet cardboard. The fix is replacing the post, not rebuilding the footing. The ledger is the other thing I always check, especially if there's any movement toward the house side or any gap. Code has improved dramatically on ledger attachment in the last 15 years — lag screws, through-bolts, proper flashing details. But anything built before about 2005 may have a ledger that was nailed rather than bolted, or that was bolted without proper flashing and is now rotted from the inside out. I've seen ledger boards that looked fine on the surface and were completely hollow from moisture and rot behind the flashing. That's the failure mode that produces sudden, complete collapse. It's not gradual."
— C.M., Foundation & Structural Specialist · 30+ Years · Construction Consulting
What You Can Safely Do vs. When to Call
✓ Homeowner-Accessible
- Probe every post base with a screwdriver for rot
- Check post plumb with a level; note direction of any tilt
- Identify the settlement pattern: one post, uniform, seasonal, or ledger separation
- Check drainage around footings and note downspout discharge locations
- Look for termite mud tubes at post bases and footings
- Restrict access if structure feels unstable or is significantly sloped
- Document with photographs for contractor/specialist review
✗ Licensed Contractor Required
- Any ledger separation from the house — restrict access, call immediately
- Post rot confirmed — replacement requires proper structural shoring
- Footing replacement or addition of helical piers
- Any shimming, jacking, or temporary structural support
- Structural repair or rebuilding of any kind
- Termite treatment and subsequent structural repair
- Any work at the ledger connection or house rim joist
Frequently Asked Questions
My porch lifts every winter and settles back in spring. Do I need to do anything?▾
If the porch returns to approximately the same position each spring, you have frost heave from footings poured above the frost line — a classic but correctable condition. The concern over time is cumulative: each heave cycle loosens post base hardware, stresses the ledger connection, and widens any cracks in piers. Even though each individual cycle appears to "reset," the structure is being stressed every winter and gradually weakening its connections. The permanent solution is footings drilled below the frost depth. For existing structures, helical piers installed below the frost line under each settling post are a common retrofit approach. Short-term: annually tighten any visible hardware after the spring thaw settles the structure; check for widening gaps at the ledger; monitor whether the "reset" position is slightly lower each year.
One side of my deck dropped about an inch. The post on that corner looks fine. What should I check next?▾
When a post looks sound above grade but the corner has dropped, check in this order: first, probe the bottom 6 inches of the post base firmly with a screwdriver or awl — rot often appears sound at the surface while the core is compromised. Second, dig away the soil around the post base a few inches to expose the concrete footing connection and look for separation between post and footing. Third, look at the footing itself: is it cracked, tilted, or partially exposed? Fourth, check drainage at that specific corner — is a gutter downspout or roof drip line concentrating water there? If the post probes sound and the footing appears intact, the most likely remaining cause is that the footing was poured on uncompacted backfill and has been slowly settling. That requires a contractor to assess whether underpinning (helical pier) or a rebuilt footing is the appropriate fix.
How do I know if my deck's ledger board is safe?▾
The exterior inspection is limited: look for any visible gap between the deck framing and the house wall, any visible rust staining at fastener locations, any decay or discoloration in the wood near the attachment, and whether flashing is present and intact above the ledger. The more important inspection is from inside: in a basement or crawlspace, look at the rim joist where the ledger bolts come through from outside. Water staining, rust-streaking from bolt holes, soft or discolored wood, or visible rot at that location indicates the ledger is moisture-compromised. A ledger that looks fine outside but has a rotting rim joist behind it is the most dangerous configuration — the visible exterior surface conceals the structural failure. If your deck was built before 2005, if there's any evidence of water penetration at the house-deck connection, or if the attachment is nailed rather than bolted, have a licensed contractor inspect the ledger as part of a general deck safety evaluation.
Key Takeaways
- The settlement pattern (one post, uniform, seasonal, or ledger separation) identifies the cause before any hands-on inspection. Map it first.
- Probe every post base with a screwdriver before any other diagnosis — post rot at grade is the most common and most overlooked cause of porch and deck settlement.
- Ledger board failure is the most dangerous type. Any gap forming at the house wall warrants immediate access restriction and professional evaluation — ledger failure can be sudden and complete.
- Do not attempt to temporarily shim or jack a settling structure. Restrict access until a professional evaluates it.
- Correct drainage around footings regardless of the identified cause — water concentration near post footings accelerates every type of failure and will worsen any repair over time if not addressed.