One of the things I enjoy about being an architect is that no two days are the same. Today I’m helping a client get building compliance on an older property in Mossel Bay — and it’s a good reminder of some important lessons when working with historic drawings.
Here’s what to watch out for.
Old Approved Plans Are a Starting Point, Not a Source of Truth
When you’re working on an older building, you’ll often be handed a set of plans that were approved many years ago. In this case, we’re looking at drawings from 1963. They have a municipal stamp on them. They look official.
Don’t trust them — at least not without verification.
That stamp tells you the drawings were approved at the time. It doesn’t tell you whether the dimensions are accurate, whether the work was built as drawn, or whether the person who drafted them measured correctly. You can and should look at old approved plans to understand what was built and what was approved, but treat every dimension as something to be verified independently.
The Cape Feet Problem
South Africa adopted the metric system in 1961, but surveyors and draughtsmen were still working in the old system well into the 1960s. That means you’ll often encounter drawings dimensioned in Cape feet — not imperial feet, but Cape feet, which are a slightly different measurement again.
A dimension that reads “80” on a 1963 drawing could mean 80 Cape feet, which converts to approximately 25.1 metres. That’s very different from 26 metres — yet 26 metres is what the stamped municipal drawing claimed.
To convert Cape feet to metres reliably, use an online conversion tool. I’ve found convertunits.com to be accurate for this purpose. Type in your Cape feet value, convert, and then cross-check against independent sources before you rely on the figure.
How to Cross-Check: The SG Diagram and the GIS
For any property, there are two authoritative sources of site information:
The first is the Surveyor General’s diagram. This is the legally registered cadastral diagram for the erf, held by the Chief Surveyor General’s office (sg.drdlr.gov.za). In our Mossel Bay example, the SG diagram is dated 1952 — older than the approved plans — but it’s the legal record of the property boundaries and is the document you should trust.
The second is the municipal GIS. Most municipalities now offer publicly accessible GIS portals with measurement tools. You can measure boundary dimensions directly on screen and compare them to what appears on your drawings. In this case, the GIS measurement confirmed 25.1 metres — matching the SG diagram and the converted Cape feet figure, not the 26 metres on the approved plans.
That discrepancy of nearly a metre may sound minor. It isn’t. If you build in the wrong position based on incorrect boundary information, you could end up over a sewer line, over a boundary, or in a situation that costs your client enormous amounts of money to rectify.
The Principle
When working on older buildings, the rule is simple: the Surveyor General’s diagram is the authoritative record of the property. Everything else — old approved plans, municipal stamps, previous survey pegs — needs to be cross-checked against it before you rely on it for design or construction.
Take the time to verify. It’s not complicated, and it could save your client — and your professional indemnity — a great deal of trouble.
— Tim Hewitt-Coleman
Director, noh Architects
Gqeberha, Eastern Cape
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