SMM7 is being retired in January 2013 and NRM2 is the new replacement.
The RICS had been working on the New Rules of Measurement (NRM2) for several years prior to the government announcing the major shift towards BIM.
The timing of the release of NRM2 and the announcement to shift to BIM will cause some difficulties for the new measurement rules in the short-term, as the industry changes towards new practice standards and contract documents.
For example, NRM2 has references to the RIBA Plan of Works, but these are being updated in late Spring 2013 to take account of BIM and a Green Overlay released in November 2011 for carbon use considerations.
The general changes will also include 5D automatic take-off and cost control principles being integrated into BIM procurement, something the NRM2 drafting process may not have envisioned.
But NRM2 should, in theory, be able to cope with BIM on the actual rules of measurement, even if the references to other industry documentation may need upgrading.
Measurement of Quantities
NRM 2 is a detailed method of measurement for capital building works and it directly replaces SMM7, which itself was introduced in 1988 as part of wider industry efforts to create coordinated project information.
NRM2 provides best practice professional guidance on the detailed measurement and description of building works for obtaining tender prices, cost planning and contract documentation.
The rules identify all the aspects that are expected to be included within a bill of quantities (BQ), including descriptions, units of measure, work considered included within items and the classification of common items.
But importantly for BIM the rules set out information required from the employer and other construction consultants.
The rules also identify:
- Those items which are non-measurable,
- Those items which a contractor or sub-contractor is required to design (which is a little at odds with the timing and method for the way collaborative BIM models are to be developed under PAS 1192-2); and
- There are various allocations for risks.
NRM2 and BIM
The NRM2 working group had its final meeting a few weeks before the Government Construction Strategy announced BIM in May 2011.
As a consequence, the NRM2 rules require professionals to consider how the rules are to be adopted and applied in the context of a market that is expected to be dominated by BIM procurement practices.
The new measurement rules should not in theory require significant changes, just a different application and approach to taking off quantities.
The RICS has started a wider review of BIM and the impact on existing practice standards.
When using 5D software to automatically take-off quantities from 3D models, the 5D software requires a set of instructions on how model data is to be re-organised.
This can require additional information being added to the model, either by the architect or the person doing the take-off.
BIM models may have extra information added to components by various members of the design team. However, it is highly unlikely that this extra model information will contain any data that is useful for a formal standard method of measurement take-off.
It is also highly unlikely that BIM model data will be in a format that easily facilities work break down structures by trade (common arrangement of work sections – CAWS) which is helpful for obtaining sub-contract tenders.
To extract information in a standard method of measurement format there are several ways to export or take-off quantities from BIM models:
1. Manual take-off from pdf’s or using free model viewers that enable a full walk around a model. Some of these can also provide the ability to measure directly from BIM model files.
2. Automatic take-off using 5D software and IFC. Industry Foundation Classes (IFC) is an industry format for exporting BIM data from 3D model authoring programs so that other software applications can accept the data and allow it to be used again for other purposes.
If you don’t have a model authoring program, someone with access to the BIM model you want to take-off will be required to provide an IFC file by saving a model in an IFC format.
IFC files are prone to some errors, either in the exporting process, the importing process or both.
3. Automatic take-off using 5D software with direct import from model authoring software.
A few 5D software programs have a direct import of BIM models. This process can be easier and it can reduce some of the errors that can occur when just replying on IFC files.
However, model authoring programs are typically updated annually. As a consequence, the 5D programs have to be updated themselves which can take several months and this can cause a few delay headaches.
4. An in-house method which requires some knowledge or assistance with programming is to create a small program or programs that extracts model data from model authoring software and dumps structured quantities into a spreadsheet. More on this in another article and in the user groups.
BIM & SMM Structuring
Most 5D software programs are designed to work on an international basis. They are not typically designed to work with specific standard methods of measurement.
If relying on automatic take-off using 5D programs, you will require a library of measurement codes which will be used to extract and compile BIM model data into a format that can be recognised as a BQ format.
These measurement codes will need to reflect an NRM2 structure, but you will have to create your own codes or buy them if the 5D supplier does not supply them – which is unlikely.
Some 5D software vendors may provide a coding structure which follows NRM1 i.e.an elemental cost planning structure; or they may have uniclass coding which is more useful for 4D processes rather than pricing and cost planning based on trade breakdowns.