What Determines the Cost of a Bill of Quantities
The cost of a bill of quantities is the cost of the work behind it. That is why a bill for a single-storey warehouse and one for a residential building with an underground car park cannot cost the same, even when the same person prepares both. Below are the six things this work depends on. With them you can judge whether a quote is reasonable and where you can save on your own.
What a bill of quantities is and how its items are organised is explained in How to Prepare a Bill of Quantities. A ready table template is in Bill of Quantities Template.
The size of the project
More square metres usually mean more items, but the work depends more on how different they are. Five identical floors take almost as long as one, because the quantities are multiplied. A building where every floor is different needs each floor measured separately.
So when you estimate the work, look at how many different things the project contains, not only at how big it is.
The number of design disciplines
A bill for the architecture alone is one job. A bill covering architecture, structure, plumbing, electrical, HVAC and landscaping is six jobs that then have to be merged into one document without duplicated items.
Each discipline has its own drawings, its own units and its own details. Electrical cables are measured in metres along the route, while structural reinforcement is counted in kilograms from the schedule. The more disciplines a bill includes, the more time also goes into checking that no work has been counted twice.
How accurate the quantities must be
A rough bill for an early-stage budget takes a few hours. A bill for a tender or a contract, against which payment certificates will later be drawn up, needs every quantity measured and verifiable.
The difference lies in the details. For a budget, the wall area is enough. For a contract you need the openings, corners, different thicknesses and waste. Every mistake here shows up later in the certificates, when the work done does not match the work agreed.
Whether there is an IFC model
When the designer has worked in BIM software and can export an IFC file, the quantities of the modelled elements are taken from the model. Walls, slabs, columns and windows come with areas, volumes and counts, without you measuring them from the drawing.
The model does not cover everything. Formwork, scaffolding, excavation, haulage and temporary works are rarely modelled and are added by hand. The quality of the model matters too: a column drawn twice will be counted twice. How IFC import works and what it gives you is described in IFC Import.
How current the unit prices are
In a priced bill every item needs a unit price. If the firm has its own prices from recent contracts and deliveries, it uses them as they are. If the prices are from last year or missing, each one has to be researched again, and that is separate work for every material and type of work.
Material prices change more often than quantities. A bill priced from an old price list looks finished, but then loses money on every item whose material has gone up.
Quantities only or priced as well
A quantities-only bill contains the items, units and quantities. A priced bill adds a unit price and an amount to every line. The second is clearly more work, because pricing is added on top of measuring.
When you compare two quotes for a bill of quantities, first check whether both include prices. Often the difference in the total comes from exactly this.
An example of how the factors add up
The example is made up and only shows how the work accumulates. Say that for a residential building with one design discipline and an IFC model, the quantities take one working day. The same building with six disciplines and no model easily takes a full week: each discipline is measured from the drawings and then checked against the others. Add a priced bill without current prices, and a few more days for researching prices come on top of the week.
For the same project the work can differ several times over, so when comparing quotes ask what they include, not only what they cost.
How to reduce the work on your next bill
Most of these factors you cannot change. The project is what it is, and it has as many disciplines as it has. Two of them depend on you, though: where the quantities come from and where the prices come from.
In Construction Team you upload the project's IFC file and the wizard extracts the elements with their quantities. The system suggests which nomenclature item matches each element type, and you confirm. Confirmed matches are saved, so linking goes faster with the next model.
You keep prices in price lists: by supplier, by type of work, with a date. When you price the bill, you see the prices from your previous contracts, invoices and price lists and do not look for them in old files.
What is not modelled and checking the model remain your work, as does the final word on every price. Measuring from drawings and searching for prices, which take the most time, become much shorter.
Related articles
Frequently asked questions
Why do two quotes for the same bill of quantities differ so much?
Usually the two firms are pricing different work. One counts only the quantities, the other adds unit prices too. One measures from the drawings line by line, the other takes the quantities from an IFC model. Ask what exactly the bill includes before comparing the totals.
Is it cheaper when there is an IFC model?
Quantities for the modelled elements come out much faster, so the work goes down. A model rarely contains formwork, scaffolding, excavation and temporary works, though, so those are added by hand.
What is the difference between a bill of quantities with and without prices?
A quantities-only bill lists the items with units and quantities. A priced bill adds a unit price and an amount to every line. The second takes more work, because every price has to be checked and current.
Can I prepare the bill of quantities myself instead of ordering it?
Yes, if you have the design and someone who knows the types of work. Quantity survey software keeps your nomenclature and prices, so the next bill starts from what you already have rather than from an empty spreadsheet.