Most homeowners notice a crack once and then forget to look again until it seems different. That second look is where the useful information is. A crack that opens a little in one part of the year and closes again in another is telling a different story from one that only gets longer, wider, or more offset each time you check.
This post is about that difference: seasonal cracks versus progressive ones. It covers what tends to move with San Diego’s seasons, what tends to move in one direction only, and why neither label settles the question by itself. Our foundation cracks page covers crack vocabulary and the cues evaluators weigh. Our earlier post on hairline vs structural foundation cracks introduces the seasonal-versus-progressive idea in a few paragraphs. Here we go deeper into the calendar behind it.
“Seasonal” doesn’t mean harmless, and “progressive” doesn’t automatically mean the foundation is failing. Direction of change over a full year is the clue. What’s causing it still takes someone on site.
San Diego runs on two different calendars
If you’re going to read a crack against the seasons, it helps to know what the seasons actually are here. The National Weather Service’s Climate of San Diego technical memorandum (TM-270) describes two patterns that don’t line up.
The rain calendar. TM-270 says rainfall in the San Diego area “is generally a late Fall through early Spring phenomenon,” running from about the end of October through April, and that “eighty-five percent of the rainfall occurs from November through March.” That’s why the Weather Service keeps rain records on a water year that starts July 1 rather than on the calendar year. The same memo warns that “wide variations take place in monthly and seasonal totals,” so one winter is a thin baseline. Its figures come from the official downtown station; TM-270 notes rainfall increases with elevation and distance from the coast, so a hillside lot above the shore may not match the downtown gauge.
The humidity calendar. The air runs the other way. TM-270 reports that humidity is above the annual average from May through October and below it from November through February, the marine-layer stretch often called May Gray and June Gloom. Our post on sticking doors and windows goes through those humidity figures and what they do to wood doors.
So the months when the ground is wettest and the months when the air is dampest fall in opposite halves of the year. That matters because soil and building materials respond to different kinds of moisture. A crack that tracks the soil may peak at a different time than a crack that tracks the air inside a wall. Before deciding what a crack means, figure out which calendar it seems to follow.
What moves with the seasons
Clay soil that swells and shrinks
The California Geotechnical Engineering Association’s homeowner guide, Coexisting with Expansive Soil, describes expansive soil as clay-rich soil that swells when its moisture content goes up and shrinks when it drops. Vertical and horizontal ground movement can both result. The City’s Guidelines for Geotechnical Reports put the same idea in regulatory terms: an increase in moisture can cause “foundation and slab uplift,” while decreasing moisture “can result in settlement.”
That cuts against an intuition many people have. A crack over expansive soil doesn’t necessarily open in the rainy season. If the clay under one corner shrinks as it dries out in late summer and fall, that’s when the gap may be widest. Rain can then swell the clay and push it partly closed.
Whether your lot has expansive soil is a lab question, not something to guess from a crack. The California Residential Code defines expansive soil by test results, including an Expansion Index greater than 20 under ASTM D4829. City Information Bulletin 141 requires a geotechnical report with building plans for structures supported on expansive soil or fill. If you have an old report from a remodel or the original construction, it may already answer the question.
Irrigation, the season you control
The dry half of the year is when sprinklers and drip lines do most of the watering. CalGeo’s guidance is to water “in moderation but also consistently,” which in practice means more in dry times and less in wet seasons, and not to shut irrigation off entirely during a long trip in dry weather. A planter bed that gets soaked three times a week from May to October, next to a side of the house that gets nothing, is its own seasonal cycle. Our coastal moisture and drainage patterns post covers how to sort those water paths.
Wood framing and finishes
Wood takes on and gives up moisture with the air around it. The Brick Industry Association’s Technical Note 18, a widely used reference on building movement, notes that wood’s moisture expansion and contraction “continues with changes in moisture content,” and that the movement is reversible. Drywall tape joints, plaster over framing, and trim at the ceiling line often crack and close on that humidity rhythm. Those cracks tend to be fine, to sit along joints and corners, and to come back in the same place after a patch. Our post on structural vs cosmetic wall cracks goes room by room.
What moves in one direction
A progressive crack is one that keeps changing the same way: longer, wider, or more offset, without closing back up. Several different mechanisms produce that pattern, and not all of them are foundation problems.
Settlement
When soil under part of a house compresses or loses support, that part goes down and generally doesn’t come back up. The City’s geotechnical guidelines treat settlement as something that can play out over time. Where significant settlement is expected, the geotechnical consultant is asked to “estimate the time for settlement to be 90% complete” and to say whether a monitoring program is recommended. Settlement can be gradual, and the guidelines expect engineers to plan for that. Our settlement repair timeline explains what happens when it’s confirmed.
Slope creep and top-of-slope movement
On hillside, canyon-edge, and bluff-top lots, CalGeo describes slope creep, where “seasonal or other cyclic wetting and drying of the near surface soils causes those soils to creep slowly down slope under their own weight.” Here the driver is seasonal, but the net movement only goes one way: downhill. A crack on the downhill side of a house can open a bit each wet season and never fully close in the dry season.
CalGeo also describes lateral movement near the tops of slopes, noting that “the lower amount of heave along the top of the slope is often mistaken as settlement.” Patio slabs pulling away from the house and widening joints in side-yard walls are among the signs it lists. Our hillside foundation repair page and the post on hillside drainage before structural repair cover that terrain.
Leaks
A leaking supply line, irrigation break, pool, or spa can keep one area of soil wet all year. CalGeo notes that a leaking pool or spa “can cause additional soil wetting and possibly even more heaving.” A leak can make a crack that used to follow the seasons start growing steadily. Finding the leak is part of reading the crack.
Materials that only go one way
According to BIA Technical Note 18, brick “is the only building material that experiences irreversible moisture expansion.” Brickwork generally grows over its service life, fastest in its first weeks and then slowly for years. Concrete masonry block does the opposite: it has a net shrinkage over time, partly from carbonation, which the note describes as “irreversible and occurs slowly over time.” Concrete shrinks as it cures and dries.
So a crack in a brick veneer near a corner, or a crack where a brick wall meets a concrete foundation, can lengthen slowly for reasons that have nothing to do with soil. Our companion post on stair-step and horizontal wall crack patterns covers how those shapes look.
Why the labels can mislead
A new site change resets the clock. CalGeo says most expansive-soil movement “typically occurs within the first few years of any changes in construction or improvements to the site (such as changes in landscaping)” until soil moisture approaches equilibrium. After that, “some longer term cyclical soil movement may continue” with the seasons. A new lawn, a removed tree, a new patio, or a drainage change can produce a stretch of one-direction movement that later settles into a seasonal cycle. A crack that grew for a while after landscaping or a remodel isn’t automatically a sign of ongoing failure, but it does belong in the conversation with whoever evaluates it.
Seasonal movement can still do damage. CalGeo is direct that some movement is “unavoidable when expansive soils are present” and that “minor cracking and cosmetic distress can still occur with properly designed structures.” It also says owners should expect “some amount of periodic (and seasonal) adjustment, repair and/or replacement” of affected features. A crack that cycles every year is still worth understanding, especially if the cycle is getting larger.
Two mechanisms can overlap. A crack can open and close with the seasons and also creep a little further each year. That combination is common enough on slopes that CalGeo calls the effects of creep and lateral fill extension “sometimes difficult” to tell apart. When the yearly low point keeps moving, treat it as progressive.
What to write down over a year
You don’t need special tools to tell the two apart. You need a record that spans both calendars. Our structural vs cosmetic wall cracks post has a simple patch-and-watch method. For this question, add a few notes each time you check:
- The date, and whether it’s been raining, dry, or foggy for the past few weeks
- Whether irrigation near that wall is on, off, or recently changed
- Whether the crack looks wider, narrower, or the same as last time, and whether one side sits higher or further out than the other
- Anything new nearby: a door that binds, a floor that slopes, a gap at a patio or addition
- Any plumbing, pool, or irrigation repairs since the last check
The goal is to see at least one wet season and one dry season. A crack that returns to roughly the same state each year reads differently from one whose starting point keeps moving.
When to stop watching and call
Get an evaluation sooner rather than later if you see:
- A crack that keeps lengthening or widening across seasons, or reopens soon after a careful repair
- One side of the crack offset from the other, or a crack that is wider at one end and getting wider
- Several cracks on one side of the house, especially the downhill side of a sloped lot
- New companions such as sticking doors, sloping floors, or a patio separating from the house
- Change after a leak, a heavy storm, nearby grading, or a felt earthquake
A foundation inspection turns those notes into a scoped look at the structure and site. When the question involves soil behavior or slope movement, we coordinate with licensed engineers as needed, including geotechnical input. For wall-only questions, our wall cracks page explains how finish and structural concerns are sorted.
Cost factors, not prices
We don’t publish repair prices. What an evaluation or repair involves depends on factors like these: how long the movement has been documented, whether a level survey or soils testing is needed, lot slope and access, whether drainage or a leak has to be corrected first, and whether the answer turns out to be finish repair, drainage work, or foundation work. A good year of notes can make the first visit more focused.
Next step
If you have a crack that seems to be changing and you’d like a calm, on-site read of what’s moving, we evaluate homes anywhere in La Jolla. Request a Free Quote, or call (650) 739-6537. Drainage questions that come up along the way are covered on our foundation drainage page.
Sources (accessed October 12, 2026)
- NOAA / National Weather Service, Technical Memorandum NWS WR-270, Climate of San Diego, California (revised September 2004): precipitation and relative humidity sections
- California Geotechnical Engineering Association (CalGeo), Coexisting with Expansive Soil: An Informational Guide for Homeowners (2013)
- City of San Diego, Guidelines for Geotechnical Reports (2008): §6.4.4 Expansive Soils, §6.4.5 Settlement
- City of San Diego Information Bulletin 141 (April 2026)
- 2025 California Residential Code, Sections R403.1.8 and R403.1.8.1 (expansive soils)
- Brick Industry Association, Technical Note 18, Volume Changes – Analysis and Effects of Movement (May 2019)