PAS 128 Explained
The British specification for finding and recording buried utilities, in plain English.
PAS 128:2022, in plain English.
What it is
PAS 128 is the British specification for finding and recording buried utilities. It does not tell you what is in the ground; it tells you how well someone looked and how much you can trust what they drew. If you are specifying a survey or reading one, these are the four things to understand.
Four survey types
Type D is a desktop search of the statutory undertakers' records; nobody visits the site. Type C checks the records on site against what can be seen: covers, cabinets, reinstatement scars. Type B is detection: the site is swept with an electromagnetic locator and GPR and every service found is positioned. Type A is verification: the service is exposed in a trial hole or by vacuum excavation and measured.
Most jobs need D plus B. A needs B first.
Quality levels
| Level | What it means | Horizontal | Vertical |
|---|---|---|---|
| QL-D | From records only | Not defined | Not defined |
| QL-C | Records matched to visible features | Not defined | Not defined |
| QL-B4 | Expected but not detected; route assumed | Not defined | Not defined |
| QL-B3 | Detected by one method; depth not reliable | ±500 mm | Not defined |
| QL-B2 | Position and depth from one method | ±250 mm | ±40% of depth |
| QL-B1 | Position and depth, both methods agree | ±150 mm | ±15% of depth |
| QL-A | Exposed and measured | ±50 mm | Per PAS 128:2022 |
Methodology M1 to M4 and the P suffix
M sets how dense the survey is, from a sweep along the expected routes (M1) to a full grid at close centres (M4). From M3 upward the GPR data must be post-processed in the office, shown as M3P or M4P and as a P on the quality level (QL-B1P). Same tolerance, more confidence, and a dataset the next engineer can reuse.
What changed in 2022
Two detection methods and a full passive sweep are mandatory for Type B. GPR arrays are recognised. Raw data must be kept. Practitioners are expected to hold a recognised utility-mapping qualification. Data sharing to the National Underground Asset Register is encouraged. The 2014 edition is withdrawn; a specification that still cites it is out of date.
How to write it into a spec
Paste this: "Utility detection survey to PAS 128:2022, Type D and Type B, methodology M3P minimum, deliverable in DWG and PDF with PAS 128 quality levels shown per utility, report to include methodology, equipment and operator qualifications."
Who does it
Our utility surveyors hold the ProQual Level 3 Certificate in Utility Mapping and Surveying and deliver surveys to PAS 128:2022.
Where it helps
- Before excavation, piling, trenching or ground anchors
- Before a basement dig or a pavement opening in a London street
- Where the statutory records are old, incomplete or contradict each other
- On a site with a history of services being added and abandoned
- When the client or principal designer has specified PAS 128
- Before EV charger, district heating or substation works
What you receive
- Marked-up ground in survey paint, colour-coded by service
- Utility drawing in DWG/DXF and PDF, each line labelled with type and PAS 128 quality level
- Report stating survey type, methodology, kit, operator qualification and limitations
- Records pack from the Type D search
- Within 5 working days of the site visit
A note on interpretation. A PAS 128 survey records what was detected to the stated quality level. It does not guarantee that every service has been found. Safe digging practice, trial holes where the drawing says QL-B3 or B4, and HSG47 still apply.
Often surveyed together.
GPR Concrete Scanning
Ground penetrating radar finds rebar, post-tension cables, conduits, and voids hidden inside concrete, before they become a problem.
Learn moreFerro Scanning
Electromagnetic scanning to map reinforcement, measure cover depth, and estimate bar diameter without touching the concrete.
Learn moreMore from PAS 128 Utility Surveys.
- PAS 128 Utility SurveysType B Detection Survey
Two detection methods over the whole area, every service positioned and labelled with how confident we are.
- PAS 128 Utility SurveysCAT and Genny Survey
A quick electromagnetic sweep for energised cables and metallic pipes, honestly described.
- PAS 128 Utility SurveysGPR Utility Survey
Why GPR is the second detection method, what it finds that a locator cannot, and where it struggles.
Got a dig coming up?
Send drawings, photos or proposed fixing locations and we'll advise the right survey approach.