Removing Slivers (Spaces)

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You may have noticed when setting up energy data in a Revit project there is a parameter “Sliver Space Tolerance”. So what exactly is a sliver space and even more important what exactly is this parameter telling Revit to do with it?

First we need to define what a sliver space is, why it is important, and finally how this parameter can help us. A sliver space is one of those small areas in your building model where you would not typically place a room object. Say for example a plumbing chase wall, or an area between a new and existing construction where a wall was framed out leaving a gap between new and old. These kinds of spaces are sliver spaces. Not every project ends up with these kinds of spaces, but many do.

Now that we know what a sliver space is, why is it important? When the analytical model (gbXML file) is created for use in energy analysis software, the way a wall is defined as interior or exterior depends on adjacent room objects. If a wall has rooms on both sides of it, the wall is defined as an interior wall. If a wall has a room on only one side of it, the wall is defined as an exterior wall. In the energy analysis interior and exterior walls transfer heat/energy at different rates, so for accurate results it is important to define these walls correctly. This is where the sliver space now plays a role. As Architects we typically would not place a room object into a chase, or a space between new and existing construction, there is no need for this. However without a room in those sliver spaces the analytical model ends up with chase walls defined as exterior. This incorrect assignment of wall will compromise the accuracy of the energy analysis.

Understanding what a sliver space is and how it affects the analytical model give some insight to what the “Sliver Space Tolerance” parameter does for us. Setting this tolerance to a value above the width of any sliver spaces you might have in the project will allow Revit to ignore spaces smaller in width than the tolerance setting when creating the analytical model. If the tolerance setting is correct you do not have to worry or go back and place “rooms” into these spaces in order to get an accurate analytical model of your project.

As long as we are talking about getting a good analytical model, I should mention there might be other small spaces (that are too large to be considered sliver spaces) that can cause walls to incorrectly be identified as exterior. Look for small areas you would not typically place a room object into. A closet or an elevator shaft would be an example. These areas are going to be too wide to be considered sliver spaces but still need to be accounted for so you do not leave “voids” in the analytical model. You will need to place room objects into these spaces in order to get an accurate analytical model. Don’t forget to use some kind of filter if you don’t want these spaces appearing in schedules.

Understanding these sliver spaces (and other small spaces) can lead to better and more accurate analytical models. Spending the extra time upfront to account for these spaces can lead to a greater reward when it comes to analyzing your building.

A Post from Jeff Hanson. Thanks Jeff!