A layer in cad is a way to differentiate between the different lines that are drawn on a page. The layer can be assigned properties such as linewieght, line type and colour and can be made visible or hidden, amongst other things.
You can use layers in a drawing for each different object type or construction element. For example, you can assign all objects or lines that are walls to a “Wall” layer. All sanitary fittings could be assigned to a ‘Fittings’ layer. Windows can have their own layer, furniture can have its own layer and so on.
Layers should be used in every drawing, no matter how large or small the project. If you are an architectural practice it is important to adopt a standardised system, or stick to a standard set of layers if you are a student, not only for good practice but also because layering your drawings can save you a huge amount of time.
Why we should never draw everything on Layer 0!
Layers allow us much more control over a drawing, and ultimately allow us to save time and money. By using a good layering system we can allocate properties to a layer and ensure the appropriate element is assigned to that layer. If later we decide we want to amend the properties, we don’t have to go through and change each individual line, we just have to change the layer properties and all the changes will appear on every line on that layer.
In AutoCAD layers are also very useful for setting up layouts and plot sheets. They allow us to control what information is viewed on different drawings. For example, on a 1:200 site plan, we would only want basic elements to be seen, so the layers that are not necessary can be switched off in that particular viewport. We would keep landscaping layers switched on, but we would turn off mechanical and electrical layers, or annotations that would be better suited to a more detailed plan, for example.
Another benefit of using layers is that you can select and modify items in bulk on a particular layer. Instead of individually selecting items that you wish to copy or amend, you can quick select all items on a layer (if the drawing has been layered correctly).
Standard Cad layers
So, I hope I have convinced you that using layers is a fundamental part of the drawing process. The next question is, what layers should I use?
There are a few different classification systems available, and this article is focussing on the use of layers in the UK. From the research I have carried out, the CISFB system which has been used widely, lacks layers for more modern systems and has resulted in practices having to modify the layering system which has created a non standard format. The Uniclass system is a little more complicated, and that has been used as a basis for the AEC UK Cad Standard. This standard was developed from 2001 onwards and provides more up to date CAD usage.
What the layers stand for:
A layer name can be broken down into fields, these fields classify the layer.
Field 1: Role
Field 2: Classification
Field 3: Presentation
Field 4: Description
Field 5: View – optional
The full details of each field can be downloaded in full from the link to the AEC [UK] cad standard document. Here I will provide an overview to the codes for each field.
The letters define the author, or owner of the data. This therefore allows various disciplines to use the same element codes all within one drawing while still being able to differentiate between the layers.
The element code describes the building element or component. It uses the single Uniclass 2015. It is possible to break down these codes into very detailed representation of building elements, but often it is acceptable to group items together into broader terms. For example, a curtain wall layer is Ss_25_10_20, but this could be denoted as Ss_25_10 which is the general code for walls.
The prefixes of these codes refers to:
SL – Spaces/locations
Ef – Elements / functions
Ss – Systems
Pr – Products
Z – non physical elements
In simple architectural terms, Ef might be used for general CAD work, Ss for detail work or components, and Pr for fit out or components that are produced. The best thing to do here is browse through the different categories, link below, to give you an idea of the different classifications in each category and when they would be used.
There is a vast list of different element codes, possibly too many…? So for the purposes of clarity, I have selected a few of the more common layer classifications to demonstrate here. Most practices would select the layers that they use regularly and create a template based on those common layers, rather than use the entire list to create a bulky file, and plenty of time wasted searching for the correct layer to use.
An example of some of the more common element codes are listed below:
The Zz category provides a layer for trees and planting which can be confused with the same in the Pr and Ee sections. The Zz tree and planting can be used for generic tree placement, and aesthetic presentation to enhance a drawing, for example an elevation or visualisation model. The Ef section would be used for generic plants in the design, and Pr for defining detailed vegetation layouts or landscaping works.
The Ef classification list is quite limited, but this allows for a more simple use of the layers at early design level, and moving on to the Ss classification as more detailed design commences.
[in 2016 the classification codes were changed quite significantly, and in my opinion have become a bit more complicated than they used to be. I still use the older system for some of the architects I work for, and for my own projects, not because I don’t link change (…!) but because it does seem a lot more intuitive and user friendly. These new classification codes take a bit of time to get used to.]
This field indicates the type of CAD data associated with the element.
These are used to describe the element of the layer, as seen in the previous table for Field 2.
These are added to part of the user description field and provide information as to how the elements are shown.
This field has become optional over time – I don’t use it myself.
So with all that said and done, lets take a look at some examples of the layers:
List of the common layers:
The key to working with all these layers is having a good template set up. This means that when you start a new drawing or project you can quickly go to your template and get started with the correct layers, rather than setting up a new drawing every time.
I have put together a list of the most common layers that I would use, keeping it to a minimum where possible. I have created a cad drawing with these layers and it is available to download. The cad drawing is a normal dwg file but can be saved as a template if you wish. All the layers are saved – with no properties assigned, that is the linetype, line weight are all by layer, and the colour for each layer is set as white. It is simple to go through and assign colours to each layer to correspond with your own plot style. Feel free to download my layer template for your own use.
I hope that this article has helped clarify the cad layering standards that are currently used today, and that the template will be useful to you. Links below to some of the reference documents that provide a more in depth look at the layering standards, classifications and codes.
If you have any questions please feel free to drop me an email or comment below 🙂