A basement page is only as good as what stands behind it. Many claims in this field come from firms selling the fix, and many rules change from one city to the next. This page sets out where our rules and figures come from, how they are checked and dated, what is only our assumption, and where our limits are.
Where rules and figures come from
We go to the source that makes or owns the claim, and link it at the claim:
- Building and plumbing rules: the International Residential Code and local codes, as actually read. The IRC is a model code that takes effect only where it is adopted, so we name the edition and section and tell you to check your local adoption.
- Moisture and drainage: university extension services, Building Science Corporation and EPA.
- Safety and health: EPA, CDC, CPSC, FEMA and state health departments.
- Discharge bans and grants: the city or state that wrote them. We name the places we have read, with a date, and never imply a national rule.
- Insurance: the Standard Flood Insurance Policy and state insurance regulators. Your own policy decides, so ask your insurer in writing.
- Pumps and dehumidifiers: maker manuals and specification sheets, ENERGY STAR for dehumidifier ratings, and EIA for electricity prices. A maker’s figure is the maker’s own, for the model named, and we rank nothing.
How a claim gets on the page
Each rule and figure is sorted by how directly it was read, and that decides how we word it:
- Read in the source itself. We state it plainly and cite it.
- Read through a summary or a third-party copy, or it is a maker’s own claim. We re-read it if we can. If not, we attribute it in plain words, such as “the maker says”, so you can weigh it.
- Not confirmed. We leave it out, or say on the page that it is not confirmed.
Some of the most repeated claims about basements failed that test. No primary source we read gives a meaning for each crack direction, a safe crack width or an acceptable amount of wall bowing. So our crack pages say what the sources do support, report the rest as what installers say, and send horizontal cracks and bowing walls to a structural engineer.
When sources disagree
We show the disagreement instead of quietly picking a side. Grading figures differ between the IRC, University of Minnesota Extension and ENERGY STAR’s builder requirements, so our grading calculator compares your slope with each one. FEMA and Iowa’s health agency give different rates for pumping out a flooded basement, so the flood page gives both, each credited to its source.
How pages are checked
After a page is written, a separate fact-check compares each rule, limit, date and spec with its source, and reworks every sum on the page. A final review looks for errors, gaps and unsafe advice. A page with a serious problem still open does not go out. Each calculator formula is tested against answers worked by hand before the calculator goes live.
How facts are dated
Every page ends with the date its sources were checked. Where a fact has its own date, such as an electricity price, a policy form or a city sheet, we give it next to the fact. If a source shows no date, we say so where it matters.
Our recheck schedule is monthly for grant programs, flood insurance rules and electricity prices, and every three months for everything else. A page shows an updated date only when its content really changed. We can’t see whether a city grant is open today, so every grant we mention carries a date and a note to check it is still open.
What is an assumption
Where we work something out ourselves, we say so:
- Arithmetic. Gallons per inch of basin or gallons off a roof are plain math, and the working is shown.
- Upper limits. Where a pump’s power is worked out from volts and amps, the result is the most it could draw, because the power factor is unknown. We say that next to the figure.
- Calculator defaults. Defaults describe an example house. Each one that is a rate, spec or rule says where it comes from and when, or that it is “our assumption”, and you can change it.
- Inferences. A conclusion the source does not state is labelled as our inference.
Calculators give estimates and print numbers only, so read the notes on the page around them. They never say that something is safe or enough. The maker, engineer, city or insurer decides.
Prices: CostPlain handles those
Lowest Floor publishes no price tables and does not estimate what a job costs. Our sister site CostPlain does, and its method page explains how: published estimates side by side, a worked build-up, and why the figures differ. We link to it for prices and do not repeat its figures here.
CostPlain is connected to us, which is why we always call it a sister site. It is also funded by display ads, so a visit there can earn ad money too. It sells no leads and makes no referrals. A grant amount or an electricity running cost may appear on our pages, with its source and date.
How we treat sales claims
Claims from sellers are reported as claims. You may see figures such as “98% of basements” or “60% of US basements” on sales pages. As of 4 November 2026, we looked for a study behind them and didn’t find one. That doesn’t prove they’re wrong, but we don’t use them.
The same goes for a claimed share of water that is surface water, percentages for how well a fix works, and lifetime warranties taken at face value. Where we report what the trade says, we write “installers say”, not “it is”. We don’t name a company when we say this, because these figures are repeated widely and singling out one firm would be unfair.
Products are described from their own specification sheets, with no “best” list and no winner. A firm that sells repairs can give you useful information, but its inspection is not an independent one, so for structural questions we suggest someone who is not selling the fix.
Our limits
Some sources can’t be read in full, because they are behind a login or block access. When that decides a point, the page says the point is not confirmed. No check catches everything, so please tell us if you find a mistake. Fixes are logged on our corrections page. Our editorial policy covers the rest of how pages are made, and finding the source of a leak is the best place to start on your own basement.
This page is general information, not engineering, legal, insurance or medical advice.
Sources on this page checked on 4 November 2026.