A bill of quantities is the list the quote is built on: how many metres of pipe in each size and material, how many chambers, bends and connections. If it is wrong the quote is wrong, and nobody notices until the materials are ordered.
What goes in
On a drainage job the bill is usually split by system, because foul water, surface water and mains water use different materials and sizes and often come from different suppliers. Within each system you want:
- The runs, in metres, per size and material. 110 PP and 160 PP are two lines, not one.
- The chambers, as a count, per type and size, with the cover's load class where it changes the price.
- Bends and junctions, as a count. They are easy to forget and expensive to get hold of later.
- The land drains on their own, since they are rarely priced like the other runs.
The order that gets it right
- Start with the scale. Check it against a size printed on the drawing, not only against the scale in the title block. A drawing printed on the wrong paper size no longer matches its own scale.
- Take one system at a time. Draw every foul water run before you start on surface water, so no run ends up in the wrong system.
- Draw run by run, from chamber to chamber. Each run then has a length you can check, and the chambers land where they belong.
- Count the bends where the run changes direction, not at the end. Afterwards it is hard to tell which changes of direction you already counted.
Where the mistakes are
The common mistakes are not big ones. A run drawn twice, a chamber counted in the wrong size, or a scale set against a line that was not the size you thought. All three show up if every run is labelled with its length on the drawing itself: you can then read the bill against the drawing instead of trusting a total.
In Mängda every run is labelled with its length as you draw it, and the bill is recounted with every line. If the tool cannot work a figure out safely, it shows no figure at all rather than one that might be wrong.
From the bill to the quote
Once the bill is right, all that is left is to price it. Do that against your own price list, with your own buying prices and mark-up, and take the client's discount off last. Then the figures are the same all the way from the drawing to the quote, and no line was copied out by hand on the way.