The Sliver Space Tolerance in Revit MEP is used to help manage narrow unoccupied spaces, like plumbing chases. For calculating heating and cooling loads it is important that all volumes are accounted for and there are no gaps in the analytical model. Gaps between spaces that are wider than the Sliver Space Tolerance will cause interior walls to be considered exterior, which will impact the heating and cooling loads. The width of the space is measured to the center line of the walls. If the gap is less than the Sliver Space Tolerance the volume will be added to the larger of the surrounding rooms.

In this example the distance between the centerlines of the walls is set to 3’.

Here’s what the analytical model looks like with Sliver Space Tolerance set to 1’ and 3’.

This will only work with parallel walls. If you have walls that are not parallel, you will need to create a separate space to make sure the analytical model is correct.