Specyfy Water
Start 2-minute check

Burst pipe water damage

A split supply line is the most common way clean water gets into a building, and the most common way a small problem becomes a large one — because it is under pressure and it does not stop on its own.

What actually breaks the pipe

Not the ice pushing outward at the blockage, as is usually assumed. When water freezes in a line it expands along it, and the pressure builds in the section of still-liquid water trapped between the ice and a closed tap. The pipe fails at that trapped section, which is often some distance from the frozen part.

It also explains the timing that surprises people. The split can form while the line is frozen and release nothing, because the ice is holding the water back. The leak begins when the thaw does.

Where it happens

Anywhere plumbing sits outside the heated part of the building: garages, crawl spaces, attics, exterior walls, and unheated basements. Age is a secondary factor; position is the primary one.

Which cities this is a live issue in is a matter of record rather than reputation. On NOAA normals, nights at or below freezing run from about 1.3 a year in Tampa to about 157 in Colorado Springs — so the same advice matters very differently depending on where you are.

What insurers are looking at

One phrase does most of the work. NAIC states that homeowners policies cover damage from a "sudden and accidental" discharge from a plumbing system, and that policies often cover the resulting water damage if frozen pipes burst.

The exception is in the same source and is worth reading twice: if your insurance company determines you neglected your plumbing system, the damage from a burst pipe may not be covered. In practice that makes documentation — photographs, dates, what you did and when — part of the response rather than an afterthought. More general coverage questions are on our insurance page.

After it stops

Clean water is the easiest category to work with and the easiest to underestimate, because it looks harmless and goes everywhere. It runs under floating floors, along joists and into wall bases, and once it has soaked into material it is on the same 24 to 48 hour clock EPA gives for anything else.

Step 1 of 3

What kind of water is it?

Where is it coming from?

Questions people ask

Why do pipes burst when they thaw rather than when they freeze?

The split often forms while the line is frozen, and the ice itself holds the water back. Nothing escapes until the ice melts, which is why damage frequently appears on the first warm day. A pipe that froze is worth having checked even if nothing leaked at the time.

Which pipes go first?

The ones in unheated space: garages, crawl spaces, attics, and anything running through an exterior wall. The common factor is being outside the heated envelope rather than being old.

Will insurance cover it?

Usually, with a condition worth knowing. NAIC states that homeowners policies cover damage from a "sudden and accidental" discharge from a plumbing system, and that insurance policies often cover the resulting water damage if frozen pipes burst. It also states that if your insurer determines you neglected your plumbing system, the damage from a burst pipe may not be covered.

How much water comes out of a split supply line?

Enough that the number is rarely the useful question — a pressurised line keeps running until someone shuts it off. What decides the size of the loss is how long it ran, which is why knowing where your main shutoff is matters more than knowing the flow rate.

It was clean water. Does that make it simpler?

It makes it cheaper and keeps more material salvageable, but the clock is identical. EPA puts the drying window at 24 to 48 hours regardless of what the water was, and clean water that sits in a subfloor stops being a clean-water problem.

Where this comes from

Start 2-minute check