North Carolina ranks #30 of 37 in the DrainDispatch Drain Risk Index, with a composite score of 25 out of 100 — among the gentler environments in the index. The median across all 37 states is 40.
What is driving the North Carolina score
The largest of the three contributors in North Carolina is water hardness.
Freeze depth: 10 inches (sub-score 12/100)
At roughly 10 inches, the North Carolina frost line is shallow and frozen laterals are rare. That removes one of the two common causes of joint movement, which means recurring blockages here are more often about grade, grease or root pressure than about winter.
Water hardness: 60-180 ppm (sub-score 39/100)
Supplies across North Carolina typically test 60-180 ppm — soft to hard. Softer water means slower scale build-up, so the effective diameter of a sound pipe holds up better over decades than it does in hard-water states.
Housing age: median year built 1986 (sub-score 23/100)
Across the 204 North Carolina towns we cover, the median home was built in 1986 (US Census ACS 5-year 2023, table B25035). That straddles the change-over from cast iron and clay to plastic. A house from this period can have either, and it is common to find a plastic replacement indoors still running out to an original clay lateral — which means the weakest section is usually the one nobody has looked at.
What this does and does not tell you
It describes an environment, not a property. A high score means buried drain lines in North Carolina face more pressure on average. It says nothing about your house. Your own pipe material, how the lateral was originally laid and whether there are mature trees over it all matter at least as much — and none of those is in the index, because none of them can be sourced state by state.
Housing age here is a state median, not your house. It is the median across the 204 North Carolina towns we cover, so it is a reasonable proxy for the pipe most homes in the state were built with and a poor one for any single address. A 1961 house on this street may have been repiped in 2015.
Version 1.0 uses three factors. Tree canopy and storm intensity are planned for 2.0. We would rather publish three factors we can source than five we cannot.
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States either side of North Carolina
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Questions
What does a score of 25 mean for North Carolina?
It places North Carolina at #30 of 37 covered states for environmental pressure on buried drain lines — among the gentler environments in the index. It is a relative measure across states, not a prediction for any individual property.
How is the score calculated?
An unweighted mean of three normalized sub-scores: frost line depth (0 inches scores 0, 80 inches scores 100), median municipal water hardness (20 ppm scores 0, 275 ppm scores 100), and housing age from the US Census median year structure built (a median of 2000 scores 0, 1940 scores 100). North Carolina scores 12, 39 and 23 respectively.
Why unweighted?
Because we have no defensible basis for preferring one factor over another. We would rather say that than invent a weighting that looks more scientific than it is.
Can I republish this?
Yes. The index is published under Creative Commons Attribution 4.0, so you are free to use, adapt and republish it, including commercially, with attribution to DrainDispatch.
Where does the data come from?
Three published sources: state frost-line depth reference tables, state water-hardness data, and US Census ACS 5-year 2023 table B25035 for median year structure built, aggregated across the 204 North Carolina towns we cover. All three are cited on the methodology page.
Does a high score mean my North Carolina drains will block?
No. It means the environment is harder on buried pipe on average. Your own pipe material, how the lateral was laid and whether there are mature trees over it matter at least as much, and none of those can be sourced state by state, so none is in version 1.0.