The decoder compares the year you enter with the period each material was used, as documented by a public source, and gives each match a high, medium or low rating. It does not know anything about your specific house.
1. A master table of dated materials
Every material in the decoder is a row in one master table, published in full on the Sources page. Each row records the years the material was used or the year it was banned, where it shows up in a house, and the source. Materials are only added when a government agency, a local utility or building authority, or a recognized inspection organization gives a date.
2. Ratings
- High: the source describes the material as common or typical for homes of that period, or the share of homes with it is high (for example, HUD estimates that about 85% of homes built before 1940 have some lead-based paint).
- Medium: the material was used in that period but not in most homes, its use was regional, or the share of homes is moderate.
- Low: possible but uncommon, or the year sits at the edge of the period when the material was used.
Where a source gives a clear start or end year, the decoder uses it. Where a source describes a period more loosely (“before the 1960s”, “the mid-1970s”), we use the nearest reasonable year and lower the rating near the edges. These boundaries are editorial judgments and are listed in the table so you can check them.
3. The decade summary
The summary at the top of your results lists the materials rated high or medium at any point in that decade. It is generated from the same table, so it always matches the detailed list.
4. What the state field does
Right now the state is used to label your checklist and to remind you that licensing rules for inspectors and abatement contractors vary by state. It does not change the ratings, because we have not yet found reliable state-level data for most materials. Regional notes will be added only when a source supports them.
5. Limits
- Renovations and repairs can remove old materials or add new ones.
- Some materials stayed in use after a ban took effect, because existing stock was installed.
- Local codes differed. Some cities restricted materials earlier or later than national rules.
- The decoder covers the materials in the master table. A material not listed is not proof that a house is free of problems.
6. Review and updates
Sources are rechecked at least once a year and when an agency updates its guidance. Corrections are welcome through the Contact page. Drafting is assisted by AI tools; every date and claim is verified against the linked source before publication.