Reinforced concrete estimating has a rhythm most practitioners trust: rebar in kilograms, concrete in cubic metres, formwork in square metres, all rolling into one BOQ without much drama. Roof trusses break that rhythm. The moment an RC residential frame reaches the wall plate and the roof structure takes over, the bill of materials changes character — and estimators fluent in RC quantities often stumble here, simply because nobody ever walked them through a truss take-off as its own discipline.
What follows is a practical, member-by-member workflow for taking off a timber or light-gauge steel roof truss system sitting on an RC residential structure — from geometry to a priced bill of materials you can drop straight into the project BOQ, with a worked example computed from scratch so you can check it against your own.
The RC portion of a residential job has one small, familiar set of units. The truss system sitting on top of it does not. The ring beam or wall plate is still RC — kilograms and cubic metres. Wall plate anchorage (bolts, straps, embedded anchors) is priced by the piece. Truss chords and web members price by the linear metre of stock. Gusset plates or connector hardware price by the piece, or by weight for fabricated steel gussets. Purlins are linear metre again, but a different section and often a different supplier. Roll all of that into one BOQ without first translating each item to a common cost basis, and a line can get silently dropped, double-counted, or priced against the wrong rate.
The second trap is that a truss looks like one catalog item — "6 m span Fink truss" — when it is really a small assembly of individually priced members. Treating it as a single line item hides exactly what an estimator needs: how many pieces, what length, what section, how many connectors.
Start with the clear span between wall plates (not the outside building dimension), the roof pitch, and truss spacing. Spacing is a practice-driven choice, not a code figure — light timber or cold-formed steel trusses under standard GI sheeting commonly fall somewhere in a 0.6 m to 1.2 m range, set by the purlin span table for your roofing sheet gauge, not by habit. Confirm against the purlin supplier's span data before locking it in.
Break every truss into its member groups: top chords (rafters), bottom chord (tie beam), and web members (the diagonals and verticals that triangulate it). List each group separately — they're usually different sections, sometimes different materials, so lumping them into one "truss timber" figure loses what you need to price correctly.
Chord length is the hypotenuse of the half-span and the rise, by the Pythagorean theorem. Web member lengths follow the same logic from the truss's panel-point layout. Where a member's geometric length exceeds available stock length, it needs a splice, and a splice needs an overlap — commonly a 300 mm to 600 mm practice allowance per lap joint, added on top of the geometric length. This is a fabrication convention, not a code figure, and it varies with connector type, so confirm it against your actual detailing.
Stock lengths rarely divide evenly into the member lengths a truss geometry demands, and every cut leaves an offcut too short to reuse. A 5% to 10% waste allowance on truss member lengths is common estimating practice — a practice range, not a code requirement — applied on top of the raw geometric take-off, before pricing.
Chords and webs price by the linear metre of stock, or per piece for prefabricated trusses bought as a unit. Gusset plates, nail plates, bolts, and straps price by the piece or by weight. Keep these as separate line items — a truss is an assembly, not one SKU, and the BOQ should show that.
Once every truss-system item has its own quantity, unit, and rate, it sits alongside the RC line items as ordinary BOQ rows — no unit-conversion gymnastics at the summary level, because the conversion already happened at take-off.
A small gable roof: 6 m clear span between wall plates, six trusses at 1.2 m on-center spacing, a basic W-type (Fink) configuration. Geometry: half-span 3.0 m, rise 2.25 m — a 3:4 rise-to-run ratio, roughly a 37° pitch, chosen here to keep the arithmetic traceable.
Member lengths per truss:
Total member length per truss: 7.5 + 6.0 + 2.25 + 3.75 = 19.5 m across 7 pieces (2 top chord, 1 bottom chord, 4 web) and 8 gusset-plate connections (5 joints on the bottom chord, 3 on the top chords).
Scaled to six trusses:
Apply a 7% waste allowance (mid-range of the practice band above), separately to the chord group and web group since they price differently:
Illustrative material rates only — ₱180/m chord section, ₱120/m web section, ₱150 per gusset-plate connection:
Roughly ₱4,570.50 per truss for structural members and connector hardware alone — before purlins, bracing, sag rods, roofing sheets, or erection labor, all separate BOQ items on top of this subtotal.
Every step above is arithmetic an estimator can do by hand — and should understand by hand, since that's what lets you catch a wrong output. But re-deriving chord and web lengths, re-splitting them into priced groups, and re-totaling every time a span, pitch, or spacing changes is exactly the repetitive, error-prone recalculation that eats an estimator's day. RHCES Estimator is built for that: define the roof geometry once, generate the member-by-member BOM automatically, apply your waste factor, and get a priced truss-system subtotal that updates instantly — then roll it straight into the same project BOQ as your RC quantities, units already reconciled.
This article isolates the truss take-off on purpose, because that's the piece that trips people up. For the whole workflow end to end — modeling a two-story RC residential building complete with its roof truss system, from geometry through a finished, priced BOQ — that full guided walkthrough is recorded as a seminar session, available here.
Hand take-off works fine for a small, regular roof like the example above — the geometry is basic trigonometry and the BOM is a short member list. Software earns its keep once you're re-running the same take-off across multiple spans or truss types, or need the output to reconcile automatically with an RC BOQ.
There is no code-mandated figure — it varies with member size, stock length availability, and how much of the truss is field-cut versus factory-cut. A 5% to 10% range is a common starting point; adjust up for smaller, more numerous cuts and down for longer runs from matching stock lengths.
Separate. Purlins, bracing, and sag rods aren't part of the truss assembly — they're a distinct scope priced against their own section, spacing, and span requirements. Folding them into a single "truss" line item is a common way this scope gets under-priced.