2D vs 3D CAD drawings

As 3D modelling in construction becomes the norm, it may seem that 2D drawings are now obsolete. That’s not the case, however, and the choice of 2D or 3D CAD depends entirely on your project and your objectives. 2D CAD is still more efficient and effective than 3D CAD for some projects.

When you’re outsourcing, make sure your design team understand when each should be used, to manage your budget and your outputs effectively.

What is the difference between 2D and 3D CAD?

2D designs show height and length without depth, like a floor plan or an electrical wiring plan. They show a flat image, so whatever is being drawn is seen from one perspective. This is usually either top down or from one of the sides. 2D CAD designs can also include cross-sections, which show features that would otherwise be hidden from outside the building or structure.

3D CAD creates models that show depth as well as height and length. A simple example would be a model of a new kitchen design that a client can navigate on screen, almost as if they were there. It creates a simulation of the objects and spaces, rather than a flat drawing.  3D CAD models show the relationships between different elements with more parameters and in more detail, so they are more complex to prepare.

Overview: strengths and limitations of 2D and 3D design formats

Here are the pros and cons, at a glance. The article goes on to explain in more detail below.

Benefits of using 2D CAD

Cheaper

2D design is less specialised than 3D modelling. It requires different expertise, less specialised software and is often completed more quickly, meaning that the costs are lower.

Clearer

Because 2D designs contain less information than 3D, they ensure everyone using them is focused on the most relevant information. There’s less chance of being distracted by elements or parameters that aren’t necessary.

Shorter lead times

2D designs are less complex and take less time to create than 3D models. If you need drawings for a small project with a tight turnaround, think 2D.

Easier to use on site

In many cases it’s still more practical to use print outs on a construction site and 2D designs can be printed, whereas 3D models can only really be effectively shown using a screen (or a 3D printer).

Limitations of 2D CAD

Less information

For a more complex design, sticking to 2D may mean more drawings are needed (more work and potentially some duplication of effort) or more testing is needed, leading to more problems to iron out on site.

Further from ‘real-life’

2D CAD results in a flat drawing, which can make it harder for clients (and others) to visualise the end result.

No automatic clash detection

Because 2D designs don’t include depth, they don’t show how all the elements (for example plumbing, electrical, ducting and so on) will interact in a 3D space.

Less efficient for complex designs

Because 2D drawings include fewer parameters for each object, they either require more work to realise a complex design (for example, more cross sections may be needed and/or more drawings from different perspectives) or give outputs that don’t properly support the construction team.

Benefits of 3D CAD

Clash/error detection

When modelling in 3D it’s easier to see inconsistencies, intersections or misalignments of different elements. This prevents costly changes once materials are ordered and construction is under way.

Convey complex info

Because 3D CAD models include depth they show the relationships of objects and design elements more fully than a drawing and are better suited to more complex designs.

Stronger visualisation

In situations where a stakeholder or a client needs to see the overall effect or a simulation of the finished project a 3D model is more powerful than a 2D drawing.

More efficient for complex designs

For larger and more complex projects, 3D CAD can show more information within one model than within a single drawing.

Limitations of 3D CAD

More expensive

3D generally takes longer than 2D design, while also needing more extensive expertise and knowledge of the relevant software packages, so the costs will be higher.

Greater expertise needed

It requires specific experience in 3D, as well as in CAD design, to create high quality 3D CAD designs, so designers who work in 3D tend to be more highly sought after.

Longer lead time

3D CAD requires more information and is more labour intensive: even simple 3D models will take longer to produce than the equivalent 2D drawings.

Needs tech to view on site

Paper print outs are still the most practical option on construction sites, but 3D models need to be viewed on a tablet or a bigger screen.

Which projects are better with 2D CAD?

We recommend 2D CAD drawings for these applications, for example:

• Floor plans
• Fire protection drawings
• Building permit drawings
• Building inspection plans
• Landscaping layouts

In general, 2D is better for drafting and schematics as it’s clearer, quicker and cheaper. If you need technical drawings, fire protection drawings, schematics or floor plans, 2D will almost certainly be sufficient and more cost effective.

In preparation for 3D modelling, you’ll usually need some 2D designs to convey the scale and size of the project, before going into the detail required for a 3D model.

You can outsource 2D design work in just the same way as 3D design work, it’s not the case that design agencies will only be interested in the larger, complex 3D CAD projects.

Which projects are better with 3D CAD?

• Ventilation system design
• Projects with complex plant, pipework or MEP requirements
• Heritage and conservation projects (which may need 3D laser scanning)
• Multi-discipline projects where designers, engineers and manufacturers need to collaborate on bespoke designs

Because it includes more information and supports clash detection, 3D CAD is well suited for projects like ventilation system design and projects requiring plant room or MEP design. It is also ideal for designs involving intricate spaces and complex geometry, like conservation projects for heritage buildings. 3D laser scanning can be used to create an accurate plan of the existing site, ready to be updated with the proposed work.

3D CAD is also well suited to projects where multiple stakeholders (like designers, engineers and manufacturers) need to collaborate early on in the design stage, as it incorporates more of the information needed by each group, allowing everyone to work from the same files.

2D and 3D CAD expertise at your fingertips

Contact our experienced team for help with all your CAD services requirements.