Pipes Here Don't Burst at 32°F. They Burst Nearer 20°F — Because of the Slab.
Southern slab houses run supply pipe through an unconditioned attic. Research puts the freezing point of that pipe near 20°F outside air — not 32. What that means in Baldwin County.
The number most people carry around is 32°F, and it is the wrong number for a house on the Alabama Gulf Coast. Field research on southern plumbing puts the point where uninsulated pipe in an unconditioned attic actually starts to freeze nearer 20°F of outside air temperature, and a survey of 71 southern plumbers put the burst calls in the teens. That gap between 32 and 20 is the difference between a dozen uneventful nights and the two that matter.
Here is why the gap exists, and why it is a construction story rather than a weather story.
Why 20°F instead of 32°F?
Water does not freeze on a schedule. It freezes when it loses enough heat, for long enough, in a place cold enough to take it — and a pipe full of moving or recently-moved water inside a heated building has an enormous head start on the thermometer outside.
The Insurance Institute for Business and Home Safety published the reasoning along with the Building Research Council field tests behind it: uninsulated pipes in unconditioned attics began freezing when outside air temperature hit about 20°F. IBHS's survey of southern plumbers agreed that burst reports "began to appear when temperatures fell into the teens."
That is not permission to ignore a Freeze Warning. It is a way to read the forecast properly. A night bottoming at 30°F and a night bottoming at 18°F are not the same event, and the second one is rare enough here that most homeowners have never seen what it does.
The slab is the reason
IBHS is blunt about the regional difference: in the South, home water pipes "are more likely to be located in unprotected areas outside of the building insulation," and houses "built on slab foundations, common in the south, frequently have water pipes running through the attic, an especially vulnerable location."
Think about what a slab actually removes. No basement. No conditioned crawlspace. The floor is concrete poured on grade, and once it is poured you are not running a new supply line under it without a jackhammer. So the builder goes up — over the ceiling, across the joists, through the attic, and down inside the walls to each fixture.
An attic in Baldwin County is not insulated space. It is outside air with a roof over it. On a clear, still January night with the wind laid down, an attic tracks the outdoor temperature closely, and a copper or PEX line lying on top of the ceiling insulation is sitting in that air with nothing between it and the sky but shingles.
Loxley is the sharpest example on our map. Its median year built is 2007 — the highest median year built of the 22 communities Streamlined Plumbing serves. Drive the Hwy 59 corridor and the I-10 corridor there and you are looking at subdivisions dropped onto what was agricultural land inside the last twenty years: the newest housing stock in the county is also the most thoroughly slab-on-grade housing stock in the county, which means the newest houses here can carry the most exposed plumbing. That is genuinely counterintuitive, and it is the opposite of how people rank risk when they are shopping.
Compare Bay Minette, whose median year built is 1976 — the lowest of the 22. Older stock brings its own problems, but a 1970s house north of I-10 is more likely to have a pier-and-beam or crawlspace section with the supply lines underneath the floor, sheltered from the sky and warmed a little by the house above.
What the cold actually did here in 2025
Numbers, from per-coordinate ERA5-Land reanalysis for the single calendar year 2025 — one year of measurement, not a climate normal:
At the Loxley coordinate, 18 days in 2025 fell to or below 32°F. Twelve of those fell to or below 28°F, the highest days at or below 28°F of the 21 communities Streamlined Plumbing serves with usable climate data. Only two fell to or below 20°F, and the coldest reading of the year was 11.1°F.
Read that as a shape rather than a list. Eighteen nights that a gardener cares about. Twelve that a citrus grower cares about. Two that a plumber cares about.
And the two that matter were not a near miss. On January 22, 2025, measured lows across Baldwin County ran 12 to 14°F at Fairhope, 13°F at Foley and 16°F at Gulf Shores, while Mobile Regional Airport recorded 6°F — a daily record, tied for the third-coldest reading in the airport-era record, and only the eleventh single-digit low in Mobile's history. Mobile also took 7.5 inches of snow that week, breaking a record that had stood since February 1895.
The three places it lets go
The hose bib. IBHS's 2024 winter guidance tells warm-climate homeowners to "pay close attention to… crawl spaces and exterior hose spigots." A garden hose left connected traps water in the spigot and turns a frost-proof hose bib into an ordinary one. Disconnecting hoses costs nothing and it is the single highest-return five minutes in this whole article.
The attic run. This is the expensive one, because gravity puts the water above everything you own. A pinhole in an attic line does not announce itself; it wets insulation, then drywall, then shows up as a stain three rooms away from the actual break. That is hidden-leak territory and it is what electronic leak detection exists for.
Exterior walls. IBHS notes that in typically warmer regions, "plumbing along exterior walls is prevalent." A supply line stapled to the exterior sheathing on the north side of a house, with insulation packed behind it instead of in front of it, is functionally outdoors.
What to do about it before the window opens
Attic insulation is the part people get backwards. Insulation on the attic floor keeps house heat in the house — good for the power bill, actively bad for a pipe lying on top of it, because you have just insulated the pipe away from the only heat source it had. The pipe needs a sleeve of its own, or it needs to be buried under the ceiling insulation rather than resting on it, or on a remodel it needs a different route.
Find your main shutoff valve now and confirm it closes completely. A valve that has not moved in fifteen years in this humidity often will not, and finding that out at 4 a.m. with water coming through a light fixture is the worst possible time. Replacing one is a short visit and it is ordinary water line repair work.
Know where the exposed runs in your own house are. Twenty minutes with a flashlight in the attic in October tells you whether you have a problem, and a Baldwin County attic in October is a far more pleasant place to be than a Baldwin County attic in July.
When repair stops being the answer
If a line under the slab has failed, we locate it and open the concrete — that is part of the work, not a reason to hand you off. But I would rather be straight about the arc than surprise you halfway through it.
One failure in one spot is a repair. A second and third failure in the same line, months apart, is the line telling you something about its own condition. At that point the arithmetic of chasing each leak through concrete stops working in your favour, and a whole-home repipe becomes the cheaper answer over any horizon longer than a couple of years. You can put rough numbers on that yourself with the repipe cost estimator before anyone comes out, and I will tell you which side of the line I think you are on before we start, not after.
If a pipe has already let go, shut the main and call. Emergency plumbing is answered around the clock at (251) 423-7654. Brandon Byrd, Alabama Master Plumber MP-4462.
Where in the county those cold nights actually land is not where most people assume, and that map is worth seeing before you decide how worried to be: inland Baldwin County is colder than the beach. Which forecast alert should actually make you act — and which one the National Weather Service quietly deleted in 2024 — is in the freeze alerts piece. The season-long checklist lives on the freeze prep page.
Sources. Insurance Institute for Business and Home Safety, "Freezing and Bursting Pipes," including University of Illinois Building Research Council field-test results and the survey of 71 southern plumbers. IBHS winter-weather-ready guidance, 2024. NWS Mobile, January 2025 snow event and January 2025 climate summaries (weather.gov/mob). Freeze-day counts, sub-28°F and sub-20°F counts and minimum temperatures are per-coordinate ERA5-Land daily reanalysis via the Open-Meteo archive for calendar year 2025 — a single year of measurement, not a climate normal. Median year built from Census ACS 2023 5-year estimates at place level.
