# Methodology

> How Retaining Wall Lab researches costs, methods and regulations: sources, cost models and limits.

Canonical: https://retainingwalllab.com/methodology/

Last updated: 2026-11-08

Every number on this site is either sourced or labelled as an estimate. This
    page explains the difference, and how a claim gets from a source document to a
    published page.

## 1. Primary sources first

    Structural claims follow the locally adopted building code and the engineer's
    stamped plan, not a manufacturer's marketing. For segmental walls we use the
    block and geogrid manufacturer's published design tables and installation
    manual. For drainage we use the same code sections the inspector cites. For
    permitting we use the local building department named on the city page.

## 2. Cost models show their inputs

    Installed cost is modelled from visible inputs: the material or equipment
    price, the labour and access scope (excavation, drain, electrical, permit),
    consumables, and a reserve for service or repair. We do not present a single
    "average cost" as if it were a quote; the range and what it includes are stated
    on the page.

## 3. How options are compared

    We compare systems on retained height per course or lift, reinforcement
    requirement, drainage detail, service life and maintenance. A system earns a
    recommendation for a stated height, soil and surcharge; no supplier can buy a
    place in a comparison.

## 4. What we have not tested

    We do not run a laboratory or a crew, and we do not carry out every job we write
    about. When a claim comes from a manufacturer document, an adopted code, a
    certification listing or a contractor report, we say which. We do not imply
    first-hand testing we did not perform.

## 5. Sources we work from

     |
       | Source type | What it decides | How it is cited

       | Adopted building code and local amendments | When a permit and stamped engineering are required | Section cited

       | Manufacturer design tables and installation manuals | Block capacity, geogrid length and placement | Table reproduced with the product named

       | Engineer-of-record plans | Site-specific design and surcharge assumptions | Plan referenced, not reproduced

       | Local building departments | Permit scope, inspection stages and fees | Office named, with its link

       | Published US price guides | Installed cost bands | Band with the month it was checked

    When two sources disagree, the page says which one it followed and why. A
    figure that cannot be traced to a document is labelled an estimate, and an
    estimate is never presented as the price of a specific job.

## 6. Listings and directory data

    The service-area directory is compiled from public business records: the
    firm's own website, its published address and phone number, and the state or
    local licence register named on the city page. A record is marked verified only
    when the name, address, phone and licence have been checked against those
    sources and the date of the check recorded; everything else is labelled. Where
    a source does not publish a ZIP code or a website, the field is left blank
    rather than guessed.

## 7. Corrections

    If a code, a specification or a listing changes, we update the article and its
    "last updated" date. Email
    [contact@retainingwalllab.com](mailto:contact@retainingwalllab.com) with the page and the correction.