When it comes to single unit homebuilding design, the industry has experienced significant changes in the way that the design is managed due to the increased use of 3D software and in particular BIM (building information modelling).

The progression of BIM software has provided a number of opportunities and challenges for homebuilders.  The focus of this article is to look specifically at how using BIM for modelling and BIM for drawings for homebuilders can be advantageous and provide time and cost benefits.

Before the impact and benefits of BIM can be discussed for each stage, an overview of design process may be useful.

The Homebuilding Design Process

The first stage of the design process is known as the concept design stage.  This involves preparation of preliminary concepts and exploring some of the options of the house.  These will be based on the proposed budget, aesthetics, location of the house and also the type of community that it will be built in.  The size, number of rooms and the generic layout of the same will be considered and developed at this stage. At this stage, the Construction materials and some consideration to sustainability will also be considered before the various plans and external elevations are created.  The concept design usually results in some plans and elevations been drawn up so that some visibility of the proposed design is in place for progression in to the next stage.

The next stage of the home design process is the design development (DD) stage, also referred to as the developed design stage.  This will see further detailing of the design and will include further consideration of the construction systems and whether high or low mass materials will be used for thermal protection in the walls, floors, and roof.  At this stage, sustainability input would also be considered and therefore solar panels or rainwater harvesting maybe added to the design.  The external and internal finishes will also be considered and added to potential drawings at this stage.  The room layout and flow of the house will also be completed during this stage.

The third stage of the home design process is known as the construction documentation (CD) stage. It is during this stage that the majority of the design documentation (also known as construction drawing sets) are produced.  It will include all of the information needed for application of building codes approval and regulations in the drawings necessary for building/statutory approvals.  It will also include detailed foundation plans and roofing plans, room layouts, window and door sizes and openings, flooring types, internal cabinetry, bathrooms and kitchen detailing.   The building services elements such as piping, plumbing, electrical, lighting and HVAC plans would also be created during the CD stage.  In addition, roofing detail, internal and external walls, ceilings, flooring and tiling details will form part of the construction drawing set also.  The most important aspect of this stage is the detailed dimensioning and sizing of all components within the house.  Typically, this stage also takes longer due to the various design options and external facade options that may exist for the house.  The CAD or drawing management element during this stage requires a lot of control and management and therefore a tool that allows such control is important.

The final stage of home design is the technical design. This usually involves external consultants for example structural consultants who are responsible for designing structural members – Floor system, Wall system, Roof structure, Foundation etc.  to ensure structural stability and safety from various forces of nature such as earthquake, cyclone, Heavy snow/rainfall etc. / reviewing the house design and ensuring that any structural elements such as steel beams, wooden trusses, concrete or block and beam flooring are adequate for the house.  The changes to CAD or BIM file will be minimal or may not result in any changes in most cases for this stage.

Given a fairly detailed process for home building design, the need to create accurate construction documents that are version controlled and allow all design detail to be captured is critical.  The question is how can BIM help to improve the quality and accuracy during this process, while streamlining the time spent on making changes to the design and therefore reducing overall design cost.

BIM as a tool does offer significant advantages on a general level and these can be summarized briefly as follows. Firstly, BIM allows the use of parametric models that are re-usable for multiple house types.  The fact that be BIM is a database driven software tool allows changes in one output area such as plans to be reflected in another of the database output areas such as in 3D model. This bi-directional associativity is a huge benefit as it prevents inconsistencies from one part of the design to another.  The usability of Revit as a rendering tool or as a model that can be exported into a more advanced rendering tools also and obviously saves time and effort for the rendering element of the project.  Another significant benefit is the online collaboration opportunity that is provided for with tools such as Collaboration for Revit (C4R). This allows multiple teams to access and work on a single housing model which is hosted on a cloud based server rather than on numerous local machines.  The other main advantage for being is of course the “information” element of BIOM, which allows specifications detail to be added to the components within the 3D model.

Looking at each stage of the home building process, the concept stage is a phase where a designer could use a simple BIM model rather than 2D plans because any changes that are made are easier to manage and a series of similar concepts are easier to create from the initial model.  It is possible that a 2D design approach may exist at this stage or a simpler form of 3D modelling such as Sketch Up to demonstrate the design.  Whichever 3D method is used, the benefit is the ability to change and experiment and in the case of BIM using a tool such as Autodesk Revit, the ability to use the model for the next stage Is useful.

3d Revit BIM Models has enabled construction companies to derive quantities of building materials (BOQ) from the model but also update them automatically when the 3d model are revised following the design changes.

The design development stage provides further benefits for when using BIM for residential construction design. During this stage, the house size and room layout changes will be more easily handled using BIM.  BIM will also allow the room layout to be created in the 3D area of Revit while the elevations, internal sections and even equipment schedules are automatically. This allows a more holistic view of the home design rather than relying on a plan view alone.   The ease of changing BIM models, either in elevation, plan or section screens results in changes to all other areas means that errors and inconsistencies are minimized.  BIM at this stage also allows simple rendered of use that provide some reference from a visualization perspective as Revit offers simpler 3D rendered views for visual purposes.  One of the most significant benefits of using BIM during the DD stage is of course the usability of this information for the next day of the home design process.

The construction documentation stage is where much more detail is added to the design and it is most likely to benefit from the use of BIM.  During this phase there will be numerous design options and design elevations that are added to the base BIM model. Additionally, the creation of drawings that are used for construction purposes will be derived from the detail that has been modelled during this stage.  The ability to change the model in a BIM environment and have that change replicated in a schedule, elevation, plan or section obviously highlights any design errors while maintaining consistency across each of these outputs.  At the end of this stage the completed model will have enough detail for the creation of a better-quality rendering that is created Revit; or the model will have sufficient detail for exporting into a 3D visualization package such as 3DS Max where better lighting and texturing can be used to create a 3D computer generated image which is a more realistic view of the final house.  The ability to add ‘information’ to each component used during the CD design stage would also be of significance to the BIM user.

Overall, BIM for residential construction can provide additional benefits compared to traditional 2D CAD tools.  At XS CAD we have experience of working with homebuilders and home designers during the last 16 years and have used BIM for homebuilding design for the last decade, ensuring that all stages of the design process are catered for by BIM technology.  As Revit Architecture and Graphisoft ArchiCAD continue to develop their software capability for BIM homebuilders with partners such as XS CAD will continue to benefit from smarter, faster and lower cost design.

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