The Difference Between Consultant MEP Models and Contractor MEP Models

The life blood of any construction or engineering project, MEP (M&E) building services are essential components of comfort for those who will ultimately occupy the constructed spaces. Flawless MEP services require detailed and efficient MEP design for design decision-making, accurate documentation, performance and cost-estimation, construction planning, management and operation of the construction project. MEP models, and how they are used, are key to comprehensively creating MEP design. MEP modelling involves consultant MEP models and contractor MEP models. It is important to understand the differences between MEP consultants and MEP contractors and then understand the models that serve them both.

In brief, MEP consultants evaluate client requirements and provide professional advice on the preferred work process, while MEP contractors generally evaluate client requirements and execute the work.

MEP consultants specialise in providing expert advice on materials to help in design decision making for MEP services. They can analyse and foresee MEP issues and then solve them. MEP consultants create MEP models, mostly with Revit MEP, which is becoming a increasingly preferred in the industry, without being overly concerned with all clashes.

MEP contractors control the MEP services, the scheduling of the work, the labour and ensures that MEP work is completed according to the guidelines, standards and schedules that have been agreed on and ensures that all the services are clash-free. MEP contractors add detailed data, such as various materials quantities, etc., to the MEP models received from MEP consultants. They consult structural and architectural models and produce clash-free MEP models primarily using Revit MEP and Navisworks.

A more detailed evaluation of MEP consultants, MEP consultant models, MEP contractors and MEP contractor models follow:


The term MEP consultant is generally used interchangeably with MEP designer or MEP engineer. Looking at what it entails to be an MEP engineer, it is relevant to understand that there are 3 main groups of MEP engineering professionals and specific services they provide. They are as follows:

Mechanical Engineers design heating, ventilation and air conditioning (HVAC) systems.

Design Elements:

  • Air distribution
  • Central utility plants
  • Utility master plan and design
  • Steam, chilled and hot water distribution
  • Exhaust system design
  • Infection control HVAC
  • Process piping
  • Building control system
  • Building energy modelling, analyses and audits
  • Renewable energy system design and analyses

Electrical Engineers design electrical systems.

Design Elements:

  • Standby power systems
  • Power distribution
  • Lighting
  • Renewable energy system design and analysis
  • Power quality assessments
  • Harmonic analysis
  • Electrical and communication systems master plan and design
  • Telephone/data layouts
  • Call systems
  • Security systems
  • Fault current analyses
  • Arc fault analyses and labelling

Plumbing Engineers design the plumbing systems.

Design Elements:

  • Domestic hot & cold water
  • Natural gas piping
  • Gas systems, distribution and alarms
  • Storm drainage systems
  • Acid waste piping
  • De-ionized water systems
  • Reverse osmosis systems
  • Water softening systems

MEP consultants or engineers ensure that structures are safe, inhabitable and comfortable. They manoeuvre through a number of constraints to produce a well-planned, analytical design that should work seamlessly and reliably. The MEP drawings that consultants create must depict the above systems individually and in coordinated form.

These drawings are derived from MEP designs with reference to client needs and whilst there is some reference to making their drawings clash free, this is not a primary concern for the consultants, or at least it has not been historically.

BIM is changing much of this for consultants because it requires the production of 3D models to create those drawings. With 3D models, clashes can be more easily identified and can sometimes make a decent design look very bad. As such consultants are paying more attention to production of 3D models that do not have obvious clashes, particularly in areas such as plant rooms, risers and main corridors runs.

The need to pay closer attention in this way has also challenged the way in which MEP consultants design and how they organise their design workflow. Historically, MEP consultant teams were able to work in design silos, where the HVAC designer and drafter worked on a building in one area of the office and the piping or electrical design and drafting team worked in a different area of the office. Whilst all had access to one another, other than some agreement on vertical and horizontal spacing at the start of the project, the teams were left to lay out the services (using 2D drafting tool) in the areas as they saw fit – approaching the design of a building with a ‘building service approach’. As there was no way to clash test 2D drawings easily, they were then issued to contractors to manage the coordination accordingly, usually resulting in several design changes by the consultant as a result of space not being planned accordingly. With 3D and BIM the approach is different and more closely mirrors a ‘building zone approach’, whereby consultant modelling teams look at an area together and model services in that area together. This more collaborative approach is further assisted by tools such as ‘work sharing’ in Revit, where users can work on the same area together and see the impact of a team member’s modelling work instantly.

The MEP design drawings which are created from BIM models by consultants are therefore better than they were, but there are still some shortfalls that are not always addressed and these include the need to allow for fitting or hanging, access and lagging. Furthermore, the models may have been created using standard/library elements which may be too small or too large compared to actual procured parts that a contractor may use.


Although on-site organisation may be prepared in advance, conflicts and delays may still occur for the MEP contractor. MEP coordination drawings are created primarily to prevent these problems before they have a chance to occur and minimise any on-site clashes. Some of the issues faced by MEP contractors include installation conflicts and time-consuming redesign of MEP elements. MEP coordination drawings tie up a project cohesively. The process of BIM (Building Information Modelling) contributes substantially to making this a reality. MEP BIM coordination consists of HVAC BIM, piping BIM, and plumbing BIM coordination services for MEP contractors. This helps in creating detailed plans, elevations and section drawings for MEP services.

The coordinated and individual service drawings help installation teams during construction. MEP contractors thus provide MEP shop drawing services and coordination services, producing realistic and ready-for-installation shop drawings. MEP contractors use BIM coordination and clash detection services to amass the information they need to identify and solve clashing interfaces between different building systems, resolving issues in the pre-construction stage and saving costs and time. Several MEP contractors also use Scan to BIM modelling services, since it uses 3D laser scanning technology to map an as-built environment and then transfers the data into BIM software, such as Autodesk Revit and Navisworks.

The checks and modifications carried out using these services by MEP contractors falls in into the process of VDC (Virtual Design and Construction). The VDC process reduces a project’s cost and time, principally by using coordination drawings to review the pre-construction design stage and include details of MEP system layouts. The coordination takes into account horizontal and vertical views, avoiding clashes between structural framing, ceilings, partitions, equipment, lights, mechanical, electrical, plumbing, conveying systems and other services.

Models for MEP contractors represent mechanical, electrical, plumbing, HVAC systems that are clash-free. To create contractor MEP models, the architectural and structural models are consulted in detail, and structural elements, such as concrete beams, steel cores, slabs, columns, etc., as well as architectural elements, such as stairs, doors, windows, internal walls, cladding systems, etc. are studied in conjunction with existing consultant MEP models to produce further detailed and efficient models. These models help contractors detect clashes and work out clash-free solutions and ultimately provide material for shop drawings or installation drawings or MEP construction coordination drawings, which can be utilised on site.

Unlike consultants, MEP contractors are responsible for fitting and commissioning of MEP services and therefore their models will incorporate additional aspects such as:

  • Accurately specified components – instead of library items, they will use models that will be fitted on site as these may differ in size or connection detail.
  • Fitting feasibility – the 3D models will sometimes feature clevis and trapeze hangars to ensure that the services can be fitted to ceilings and walls
  • Accessibility considerations – as services require maintenance during a building’s life cycle, the MEP contractor’s models will include access hatches and access space to reach the elements of the services that may require maintenance.
  • Fabrication intent – MEP contractors are increasingly pushed for faster delivery on site and therefore creation of engineering modules for areas such as plant rooms, risers and corridors may also be incorporated in their 3D models. This will usually result in off-site manufactured steel-based frame structures that hold all of the core services, such as ductwork, piping, drainage, electrical and fire services.

In many ways, the above elements cannot be considered by consultants, as they are creating their models too early in the process. However, some aspects (such as accessibility) are increasingly starting to feature in consultant models too.

Revit MEP is a popular software tool among MEP contractors to create 3D models, as well as builder’s working drawings, fabrication drawings, shop drawings, collision detection, detailed section reviews, schedules and bill of materials etc. Shop drawings portray plans, elevations and sections. They depict structural grids, composite drawings, electrical component technical drawings, underground and above-ceiling coordination, sheet metal drawings, ductwork drawings, pipe fabrication drawings, plumbing drawings, equipment placement, etc.

Other than the use of Revit as a delivery platform, the MEP contractors’ process or approach for MEP coordination is vital, as it is a ‘building zone approach’, whereby his modelling and coordination teams look at all services within each area as they model and remodel their BIM 3D models, utilising Revit’s worksharing feature to see each other’s work as they progress. This way, clashes are minimised during the initial phases, and although interference analysis checks are regularly undertaken, they are there to check tolerances as opposed to identifying modelling errors and significant clashes.

MEP 3D modelling services, MEP BIM, HVAC BIM and construction documents are extensively useful by MEP consultants and MEP contractors in the construction industry. Services that involve 3D MEP coordination and clash detection ensure both efficiency and cost saving for residential, commercial, healthcare and education sectors. Appreciating the difference between MEP consultant models and MEP contractor models, the depth of information they provide and the related drafting and modelling services available helps plan and execute construction projects expediently.

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