Walls in Autodesk Revit

Just like in the real world, Walls in Revit Architecture are built from individual materials layered one on top of the other. Each of these layers, both physical and digital, have important roles in construction and in Revit.

The roles of these layers (structure, membrane, finish, etc.) are represented by a series of numbers (or more accurately the hierarchy of the numbers) to decide how they should clean up with adjoining walls.

5's clean up with other 5's, 4's with 4's, etc. Smaller numbers are more important (at least in construction) than larger numbers and determine which element has priority when walls join and how they clean-up with each other. Lower numbers always pass through higher numbers when they meet. In addition, layers have to have the same material applied to them in order for them to join properly.

The hierarchy of numbers and the names of their roles:

1 - Core - The structural core of the wall.
2 - Substrate - A secondary structural layer for the application of finishes
3 - Thermal/Air Layer - Typically for rigid insulation in cavity wall construction but also potentially useful within the Core
4 - Finish 1 -Interior finish layer that, in this context, is misleading as it is not ideally suited for paint and other thin coatings. It is useful as a layer of gypsum wallboard or wall tile.
5 - Finish 2 - Exterior finish layer that is the same as the interior finish layer and only separated in the hierarchy for special conditions

There is one more layer that doesn't play a part in the numbered hierarchy.

Membrane - Zero thickness layer for air/moisture infiltration barriers and the like. I haven't found a use for this other than allowing the wall construction to be technically correct. You can't tag it and it doesn't appear differently in any view.
These layers are placed one on top of the other from the exterior to the interior to form a representation of the walls physical counterpart.

If you expand the Walls Edit Assembly dialog box (by clicking the the Preview button at the bottom left) and change View to Section: Modify type attributes you can select the top or bottom horizontal line segment of a layer to unlock it from the adjacent layers. This allows you to move these layers up or down in a section or 3D view.

This is useful for walls where the, for example, the core layer extends further than the finish layers.

There are a couple of problems however.

1. You have to do this manually for each wall instance altough this can be done from the Walls Element Properties dialog for multiple walls.
2. If the wall is attached to a floor, ceiling or roof it won't work.

There is also no way to easily tell which walls have there layers extended and which don't without examining them in sectional or 3D views or reviewing the walls properties.

There are several ways to handle this issue that might be better.

The first is to not deal with it at all. Unless the extension is noticeable in multiple views you can accomplish the same look graphically by using Edit Cut Profile and removing the portion of layers that are not needed. The downside to this method is that it doesn't schedule accurately and that may be reason enough to try another approach.

Another solution is to use multiple Wall Types and layer them together in the project. For a typical interior wall you might use 2 Wall Families - one for the structure and one for the finish - and place each next to the other in the same way you would do if you were building the wall by layers in the Edit Assembly dialog. This is a very time consuming process but provides a great deal of control both in the placement of the components and in the accuracy of the schedule. Contractors using Revit will often construct walls in this manner.

The last idea is to create a Stacked Wall with the lower walls height set to where the change occurs and to use a wall with different construction above to match the desired condition. The downside to this approach is that you'll need as many stacked walls as you have conditions and they all have to be managed.

The best solution is certainly some combination of all these methods. Circumstances will dictate which to use and when.

Walls are placed in Revit as two-dimensional lines Which part of the wall this line represents is controlled by its location line. There are 6 places on the wall (both real and imaginary) that Revit can use;

• Core Centerline - the geometric center of the core components
• Wall Centerline - the geometric center of the wall construction
• Core Face: Exterior and Interior - the line that forms the outer edges of the core components
• Finish Face: Exterior and Interior - the outer edges of the wall construction

Each wall has its own location line that can be changed as needed. When changing a walls Type it is important to know which location line it's using so that you'll know how the wall will change.

If a walls location line is set to Core Face: Exterior then as the wall changes width (whether through changes in the walls construction or the walls type) this line will remain in the same location and the wall will grow or shrink on either side of the line.

If you can predict how the wall may need to change in the future you can use a location line that will make things easier.

As an example, the most important location line on a typical exterior cavity wall with a masonry core is the Core Face: Exterior. This line sets the slab and foundation edges and, once established, should ideally never move with changes to wall construction. By using the correct location line when the design changes from a brick exterior to EIFS updating the model is relatively quick and painless since you won't have to move the walls after the revision.

Two small opposing arrows on one side of the wall seen in plan represent the walls exterior. Clicking these arrows will flip the exterior and interior faces and construction of the wall about its location line. When initially placing the wall if you notice that the exterior face is on the wrong side (most notable when you are using something other than one of the two center location lines) you can press the space bar to change which side is exterior.