[MEP Center Engineering]

Starter question — a frequently asked question posted by the MEP Center team to open this forum. Share your own experience below.

I am preparing the bill of quantities for the plumbing and heating of a residential block from 2D drawings. I measure pipe lengths on plan, but quantities always come out lower than what the contractor installs.

• How should pipe be measured: centreline, through fittings, with or without vertical runs?
• Should fittings, valves, insulation and supports be separate items?
• What waste allowance is reasonable?

[MEP Center Engineering]

Measure pipe along its centreline, by system, material and size, continuously through fittings and including all vertical runs, then add fittings, valves, insulation and supports as the measurement rules of the BOQ require. Most shortfalls come from missed risers and drops, not from plan lengths.

Measurement rules in practice

1. Agree the method first. UK NRM2 practice measures pipes over fittings and enumerates fittings as extra over the pipe. Many national unit-price systems instead have pipe items that include fittings in the rate. Read the item description and measure to it.
2. Separate items by system (cold, hot, recirculation, heating flow/return), material, size, and location if rates differ (in shaft, in ceiling, buried, exposed).
3. Include vertical lengths from sections, riser diagrams and fixture connection heights: risers, drops to fixtures, rises to radiator valves, offsets around beams.
4. Fittings and valves are enumerated by type and size (elbow, tee, reducer, union, valve).
5. Insulation is measured by pipe size and insulation thickness, usually to the same lengths as the pipe it covers.
6. Supports are measured either as an item in the pipe rate or enumerated from the spacing in the specification.
7. Waste: do not add waste to the measured BOQ quantity if the measurement rules say “net”; the contractor prices it. For a material estimate, 3-5 % on pipe is a common allowance.

Worked example: a DN25 galvanised distribution branch

• Horizontal length measured on plan: 42.6 m.
• Six drops to manifolds of 0.8 m each: 6 x 0.8 = 4.8 m.
• Net measured length: 42.6 + 4.8 = 47.4 m (the BOQ quantity).
• Material estimate with 5 % waste: 47.4 x 1.05 = 49.8 m, ordered as 50 m.
• Fittings counted on the drawing: 14 elbows, 6 tees, 2 isolating valves.
• Supports at an assumed 2.5 m spacing from the specification: 47.4 / 2.5 = 19 spaces, plus extra supports at each drop and valve.

Here the drops are 10 % of the plan length. On a typical floor with many fixture connections, vertical lengths can be a larger share still.

Practical tips

• Measure by layer or system on a copy of the drawing and colour what has been measured.
• Keep a take-off sheet with drawing number, revision and location for every line, so revisions can be updated.
• Check scale on scanned or PDF drawings against a known dimension before measuring.
• From BIM models, export by system type and size, but check that fittings are not being counted as pipe length and that unconnected or duplicate elements are removed.

Common mistakes

• Double counting at drawing match lines or at the boundary between floor plans and riser drawings.
• Missing equipment connections in plant rooms, which are dense with fittings and valves.
• One item for all sizes, making the BOQ impossible to price properly.
• Insulation forgotten on valves and fittings where the specification requires it.

Related: MEP quantity take-off tips, How to draw a clear MEP riser diagram.

Check the edition of the code that applies to your project.

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