The ideal quantity take-off: how do they do it ?

The ideal quantity take-off provides information to the developer, the designer and the contractor.

How do they do it ?

The backbone of this QS are the objects the designer works with. From there you take sidetracks towards floor surface to gain knowledge for the developer and towards materials to come to the full shopping list for the contractor.

How detailed do you need to work ?

This depends on the phase: when you are only considering to invest, you will determine the cost on a much more global scale than when you're preparing the start of the works on site.

On www.bouwdata.net at the "download" page you find the Excel file with theObject Code in Dutch to start from.

In the left top corner you see 4 groups:

• group 1 is the structure of costs according to the investment standard NBN B06-003, the standard for costs related to facility management NBN B06-004 (both dark blue lines) and table 6 of the NEN 2634 (light blue lines) which connects the investment standard to table 1 of the international classification system SfB. 
  But for daily practice, this is too vague. 
  So we move to group 2 to get started.
   
• group 2 are the things you have to put a price on when you consider to invest.
  According to the NEN 2634 one only needs to put figures behind the dark grey lines, the "element clusters", table 7 of this standard. But in order to make a proper decision between several options I dig deeper. The light grey lines - "elements" according to table 8 of the NEN 2634 - and white lines - "components" according to the BB-SfB (plus) - you see in group 2, are the checklist to follow. In the next phases (groups) more of them will appear.
   
• group 3 you use when you are working on a structural design. 
  This is often called the "provisional" design phase. But there is nothing provisional about it ! The moment you decided to go on with the investment, you started working on a layout plan, you determined where the loads will go to the foundations and where the technical shafts would come. I can't imagine that, once this job done, you consider to do it all over again because you changed your mind overnight. My advice: go slowly but steady forward in this phase and consult every teammember involved. This way you won't have to start all over again.
   
• group 4 you use when you are completing the design. 
   

Group 4 is the level where the top-down of the designer meets the bottom-up logic from the contractor. The emphasis is still on fonction. E.g. everything concerning windows in the facade is to be found together in 2D.31:  the beam above to support the facade and inner wall of the facade, the window itself, the plasterwork on the sides, the tablets and all ornaments around the opening. 

Why ?

Well, the designer works with models. When he removes a window, everything related to this particular window has to be cut out of the cost. And the designer doesn't want to look at ten places in the QS to do so.

On the other hand, when the contractor needs to put a price on a project, he doesn't want to look at ten places in the QS to find all the plasterwork, either.

So, what do we do ?

Well, the moment we start determining the materials, we add an extra column.
On www.bouwdata.net at the "download" page you find the Excel file with the Material Code in Dutch to work with. As explained in one of my first articles on this blog, I use the STABU standard instead of table 2 and 3 of the SfB.

You are used to a QS in a single tab of an Excel file. 
To have an ideal QS for both the designer and the contractor, we are going to add an additional tab with the material code in the lead. Through the formula "sum.if", you can reorganise the QS you allready made into a shopping list for the contractor.

How ?

By moving forward to real construction cost engineering, and adding the cost type (labor, material, equipment or subcontractor) and a unique number (e.g. the article number of the supplier) to the material code. Once you have this, the "sum.if" formula turns this second tab into the complete shopping list for the contractor.

Now two partners have their ideal QS. What about the third one, the developer ?

He is interested in costs related to the big surfaces and in an analysis of the floor surface: gross floor space versus net floor space; salable floorspace versus net floor space.

When we look at the exemple of the window, the different levels of the object code will do.
In the tab of the material code, you enter a price per unit.
In the tab of the object code you add another column. 
With the "vertical.search" formula you retrieve this price per unit from the tab with the material code. 
In a next column in the tab of the object code, you multiply this price per unit with the quantity of the component (smallest particle of the object code). This gives you the total price per component. 
E.g. the sum of all the components of 2D.31 divided by the total surface of all facade openings gives you a figure per square meter facade opening. 
Store this in a database together with a solid project information sheet and the developer will get, over time, a good source for budgetting next projects.

But a developer needs more. On www.bouwdata.net at the "downloads" page you find the Excel file with the Development Code in Dutch to work with. This is a mixture of common sense, the Uniformat Classes and a variation on the coding of spaces in the Dutch Bouwbesluit.

Add this as a third tab to the QS.
I usually put this one first, then the tab with the Object Code, followed by the tab with the Material Code. Development is to be recognized by red-grey colours, Object by blue-grey colours and Material by green-grey colours.

When you go back to the Excel file concerning the Object Code you will see in the 4th column how this Object Code is related to the Development Code. By deviding the cost of the Object Code to the quantity of the, in column 4 mentioned, Development Code, you get e.g. the cost of the architectural and structural works per m² gross floor surface.

As a general rule I state that, with every item you want to measure, you ask yourself to which room this belongs (this is mainly the case with finishings and certain parts of the technical installation), which function it has (e.g. will it disappear when the window is removed from the model ? If so, put it onder 2D.31) and of which material it is made.
Whenever you work your way through the project in this methodological manner, you will certainly come to the ideal QS for the developer, the designer and contractor all at once.

But be aware: it remains a hideous job no matter whether you do it by a simple Excel file or by adding parameters in a BIM software.

Kind regards,
Peggy