Do you have trouble imagining what your house or extension will look like? With ‘flat’ 2D plans and drawings it can be hard to get a sense of scale and proportion. 3D Modelling is the way forward.

It all too often happens that self-builders think they will get one type of a look and end up with quite another due to a misunderstanding of the 2D plans. It takes years to train someone to interpret complex 2D plans, so this is a common problem. Of course there are ways around this, such as visiting similar houses, but the bottom line is you don’t want to be living in your home with a ‘what if’ frame of mind!

With 3D modelling there’s much less guesswork involved as you can see the house from any angle you wish – the model moves as you please. Furthermore the design can be virtually checked, verified and assessed at all stages of the process.

You may not even have to pay above the usual design fees to take advantage of this technology as 3D modelling is increasingly becoming integrated into standard architectural services. In fact architects prefer that clients sign off on the design with a full understanding of both 2D and 3D details, to prevent disappointments but also to avoid changing the design during the construction stage, e.g. window or wall placement, which can lead to significant additional costs and confusion on site.

It’s important to note that even though all designers are able to do up standalone 3D images (this will come at an extra cost and will only give you a fixed view) not all designers use modelling software. And don’t be put off by the common misconception that 3D modelling is only for very large projects, it’s in fact ideally suited to one-off houses, extensions and refurbishments, and has been used successfully for that purpose for over a decade in Ireland.

2D workflows

The most common method to record a house design is to first put pen to paper with hand drawn perspective views and sketches, then input the information into Computer Aided Design (CAD) software, the computer version of pen-and-paper drawings.

Floor plans, sections and elevations are created independently from one another and therefore any new views have to be created from scratch; if you change a window you will have to edit not only the floor plans but all views in which the window appears.

Errors can easily happen if the designer forgets to change one of the views. And you end up with many versions of the same plans; it’s actually not uncommon for various tradesmen to be working to different ones, causing significant problems and/or delays on site. While CAD has brought about efficiencies and scalability to the drawings and dramatically improved the work processes involved, the approach is time consuming and of a fixed view. If you want to see the design from a different angle then you need to start again. For those who want a 3D model, information has to be inputted again into a different software package to throw up the (fixed) three dimensional view which leads to the duplication of information.

BIM render of a house extension in Co Tipperary; the information for the light fittings was downloaded from the manufacture’s website (Osram) which came with pre-set light values.

3D modelling workflows

In the construction world, full-fledged 3D computer modelling is referred to as Building Information Modelling (BIM), which provides many more design tools than just 3D plans.

Data held within the 3D computer model allows for a collaborative process of designing, constructing and managing the project from inception to operation. With BIM you input the design information once, into an initial model, and any new information you wish to add or alter is layered on top of the original. When editing the 3D model, a change in plan is instantly reflected in section, elevation and perspective views, the software automatically makes the changes so there’s a lot less room for human error.

2D plans, sections and elevations are essentially a by-product, not the starting point, a fundamental difference between the 2D and 3D modelling design approaches. This allows for a much more efficient design, truly tailor made; the designer can play around with the model to decide what the optimal siting or specification should be. Furthermore this data can be accessed throughout the lifecycle of the building for those who want to track how it’s performing – as many self-builders do!

BIM’s data-rich model provides a wealth of design information that can readily be used. The basic package you will be offered by your designer will generally be the 3D model along with environmental analysis (for optimal building envelope specification); add-ons are then possible for things like immersive design (a walk through the house with actual finishes), analysis such as ventilation flow rates, solar thermal specifications and the sizing of your heating system including evaluating which type will be more cost effective (gas vs oil vs heat pump vs biomass).

Of particular interest is the ability to readily draw up a bill of quantities from the specifications contained in the model, which makes it easy to compare prices from different suppliers and/or form the basis of a tender package. You can continue to use this facility during the build to keep on top of the budget and readily calculate any overruns if something unexpected happens and a redesign is necessary.

Another important advantage from a design point of view is the fact that critical junctures are flagged by the software; these may be overlooked when doing 2D drawings but with 3D, insulation gaps can quickly be highlighted and the ‘tricky junction’ brought to the attention of the builder at an early stage.

Indeed, another benefit is that BIM makes it clearer for builders too; as the information is more comprehensive and has gone through extensive clash detection phases there’s less possibility for misunderstanding or costly mistakes to happen on site. Contractors are also becoming more internet-savvy and as such are increasingly using BIM platforms to consult and comment on the model/plans before the construction begins, as well as during it as an instant messaging platform (to instantly communicate with the project designers and clients).

Appointing your BIM designer(s)

Depending on the designer you choose, the BIM offering will differ. Some add-ons may be included as part of the standard package, others not. Designers will have developed an idea of which add-ons are worth their while and they may for instance prefer the ventilation flow rate be calculated by the ventilation supplier (if the system wasn’t sized correctly the supplier will then be responsible).

The bottom line is to make sure you understand what the standard design fee includes and how much any add-ons might cost. Discuss at an early stage what you may or may not need from the BIM offering with your designer.

Due to the large number of different BIM software packages that are available, an open standard known as IFC was created to allow them to interact with one another (see info at end of article); much in the same way you can export a Word document to a Rich Text Format the model retains the essential information (dimensions/specifications) but loses some of the finer formatting details (such as finishes). This allows you to choose any engineer (or other professional with an input into the design) you’d like to work on your project and not necessarily one that has bought the same BIM software package as your architect.

Many of the BIM packages available can readily export the data contained within the model to the passive house package (PHPP) or BREEAM. However there’s still work going on to link export data that’s easy to input into software that’s used for statutory calculations.

At Waterford Institute of Technology a project is comparing a BIM authoring tool and the DEAP methodology (ROI’s official method for calculating BER and compliance to building regulations). If all the same backstop values can be entered then BIM could theoretically also generate the energy rating and certify compliance to the building regulations.

Components of a self-build

The initial stages of the project are the same whether undertaken in CAD or BIM: identifying the brief, budget and a site visit.

From here the process starts to diverge, yes, the design is sketched on paper but this can then be quickly developed into a 3D model using a variety of BIM authoring tools. Here’s an example of a house in Co Kilkenny which is now seeking planning permission.

The house has beautiful views on one side and sunlight on the other; the balancing act here consists of making the most of both aspects.

Information hub

Prior to meeting the clients we set up a ‘Common Data Environment’, this is a cloud based repository of information that the design team and clients can access. It allows you to comment directly on the dynamic 3D model. This enabled us to review the design with the client along with comments from the initial planning meeting.

Some platforms offer the possibility to walk through and explore the house as you would in a video game. (Through Waterford Institute of Technology’s research group this technology is being developed in conjunction with virtual reality headsets.) While working with the 3D model, the client was able to visualise how light enters the space and how each room/area interacts with one other. This was especially important in this house as the north facing aspect is the one with the views.

On the basis of the analysis the client decided to change the windows in the living area to allow more light in. Thanks to the walk-through facility, it also gave them a feel for the living and kitchen space which was also altered to allow for a strategically placed rooflight.

The design evolved to open the building out to the south west to capture the daylight from morning to evening. From the two daylight studies there is a marked improvement in the lux levels in the living area.

“The light analysis data and shadow study movies, which we have for each area of the build have been invaluable in helping us decide what works and what does not,” said the homeowner. “Also, because the topological data was fed into the model, we can clearly visualise how the new build works with the site and the surrounding area.”

A major benefit from the clients’ point of view was to have access to the cloud platform from his smart phone; on his way to work in the train he would play around with the model and communicate with his architect. He quickly got to grips with the functionalities and was able to comment on individual aspects as the design evolved.

Mapping out the site

For a one-off house a topographical survey is recommended; this provides 3D information on the site levels, boundaries and importantly the road alignment if we are dealing with access / egress sightlines, something the planners are always interested in! This information is CAD based and imported to the BIM authoring tool and a 3D topographical surface is created.

The 3D software will ask you to locate the house and with this information, it will automatically check the nearest weather station for data so it can run the various analyses and simulations required to design the house.

This particular site has beautiful panoramic views from South West to North West, so it was important to capture these whilst maintaining a good level of daylight into the rooms. The initial design model was created and within the 3D software, an environmental analysis was run.

Environmental analysis

The environmental analysis provides energy consumption data, solar study, shadow study, and daylighting analysis to determine the amount of light (calculated in lux) that will reach occupants inside the house, at 750mm above floor level. This is used to establish whether suitable lighting levels are achieved for specific tasks.

As windows are much less efficient at retaining heat than walls are, we use a combination of daylight analysis and thermal envelope analysis to optimise the external build up.

Shadow analysis movies are also created for each of the four key seasonal dates: winter and summer solstices, spring and autumnal equinoxes.

Gordon Chisholm & Astrid Madsen

Gordon Chisholm MCIAT, MRIAI, BIM Collective Research Group, Waterford Institute of Technology and of ChisholmARCHITECTS, Crail House, Ennisnag, Stoneyford, Kilkenny, tel. 056 772 7095,

Additional information:

Bernard Voortman MRIAI Dip Arch. (BE) M(Sc) Urban Design, Director & Senior Architect/urban designer at Cummins & Voortman Ltd., Dublin Office 01 2966507, Tipperary & Kilkenny Office: 056 7755745,

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