Houston The One Part of Your System a Freeze Can Actually Reach
Everything that carries water through a Houston irrigation system is buried — the mainline, the lateral pipe, the valves sitting in their boxes a few inches under the turf. All of it is protected by dirt that never gets cold enough to matter here. There is exactly one exception. The backflow prevention assembly has to stand above ground, and above the highest sprinkler head on the property, or it can't do its job of keeping irrigation water from siphoning back into the drinking supply. That requirement is also what makes it the only component in the whole system a hard freeze can get to.
Water expands roughly a tenth of its volume as it freezes. Inside a sealed brass or plastic casting, that expansion has nowhere to go, and it splits the housing — classically right through the domed bonnet on top of a pressure vacuum breaker. It doesn't take a week of hard freeze to do it. A single overnight dip is enough, and Houston has produced one almost every year lately: February 2021, December 2022, January 2024, January 2025. None of those were long cold snaps by northern standards. All of them cracked backflow assemblies across the metro.
Four Steps, About Fifteen Dollars, Before the Next Front
The fix isn't complicated and it doesn't require any tools you don't already own. It does require doing the steps in the right order.
- Close the irrigation isolation valve — the shutoff dedicated to the sprinkler system, upstream of the backflow assembly.
- Open both test cocks and part-open the shutoff handles so the assembly drains completely. This is the step people skip, and it's the one that matters most.
- Insulate the whole assembly — a foam cover or wrap plus a plastic bag over the top to keep wind and moisture out.
- Turn off or reprogram the controller so it doesn't fire a zone through a freezing device on a freezing morning.
An insulated cover slows heat loss, but it doesn't stop water from freezing outright over a long enough cold snap — it buys the assembly time. If there's standing water inside when that time runs out, you've just insulated the exact water that's going to crack the casting. Drain first, then wrap. A foam cover and a bit of tape run somewhere around the price of lunch. A cracked assembly is a mid-hundreds-dollar replacement, plus a wait if half the metro is calling about the same thing at once. If the bonnet's already cracked or the assembly is leaking now, that's a job for a proper repair rather than a wrap — see the backflow preventer repair page for what that looks like.
Why Not Just Blow Out the Lines Too
Homeowners who moved here from colder states sometimes ask about a full blow-out, the way it's done up north. It's not needed and it isn't always possible. Ground temperature at irrigation pipe depth on the upper Gulf Coast doesn't get near freezing even in a severe multi-day event, so the buried mainline, laterals, and valves come through fine with water still in them — they did in February 2021, when the damage that made headlines was almost entirely inside attics and exterior walls and in exposed outdoor fixtures, not underground pipe. Most systems built here also have no blow-out port to begin with, and rigging one up turns a seasonal chore into a plumbing modification. Compressed air pushed through a system that isn't built for it can tear valve diaphragms and strip rotor gears — a bigger bill than the freeze was ever going to cause. The backflow assembly is the whole story. Handle that one component and the rest of the system doesn't need winterizing at all.
Bringing It Back Up in Spring
The reverse matters just as much as the freeze prep. Open the isolation valve slowly — a drained mainline refills through empty pipe at high velocity, and snapping it open fast can break fittings the freeze itself never touched. Watch the backflow assembly before any zone runs; a hairline crack shows up the instant pressure hits it, not before. Then run every zone individually and watch it. Some damage — an internal seal nicked by ice, with the casting still intact — only shows itself under pressure and flow. This is exactly the kind of thing worth catching during a full spring startup system audit rather than three months later when a zone quietly stops working.
This applies whether the assembly sits in a Cypress front bed, a Sugar Land side yard, or anywhere else across the coverage area — check service areas for the neighborhoods this reaches directly.
The whole job takes less time than finding the foam cover in the garage: close the valve, drain the assembly, wrap it, kill the zone schedule, and the coldest night of the year becomes a non-event instead of a mid-hundreds-dollar repair.