# Creating 2-sided faces problems

Hello,

I am having some trouble reliably creating 2-sided faces. Reviewing the Symscape website, I came across this procedure and have used it with some success:

"Subtract the original pseudo volume attached to the face
Submitted by symscape on August 23, 2013 - 11:01.
Make sure you:

Enable the Topology Only property under the Booleans->Subtract tool
Selected the Face (membrane) not the pseudo Volume (this face shouldn't strictly be a volume as it doesn't enclose a volume) as the final operand in the Subtract operation
Delete the original pseudo volume attached to the face - the face will remain as it is still part of the new volume
Then perform the Faces->2 Sided operation."

My simulation involves a primary simulation volume and two pseudo volumes.

One pseudo volume is simply a single face I wanted to embed in the primary simulation volume. I subtracted that single face from the primary volume, then deleted its pseudo volume. Then I made the embedded face a 2-sided face exactly as detailed above. It was very easy.

The second pseudo volume consists of 25 adjacent faces at ~ 90 degree angles to each other (analogous to staircase steps) that I also embedded into the primary volume. At one end of the “staircase,” the first of the 25 faces is attached to the primary volume on three edges. It is attached to the second “staircase” face on its fourth edge (as a bottom step is attached to the floor, both sidewalls, and the next step). The next 23 faces are each attached to adjacent “staircase” faces on two edges and to the primary volume on two edges (as intermediate steps are attached to both adjacent steps and both sidewalls). The last of the 25 “staircase” faces is attached to the previous face on one edge and to the primary volume on two edges. It is not attached to anything on its fourth edge (like a top step beyond which there is no floor).

To embed this geometry, I again:

Subtracted each face of this "staircase" pseudo volume individually from the primary simulation volume. This gave me the primary volume with the "staircase" faces embedded within it.
Deleted the pseudo volume.

However, when I try to individually convert these 25 “staircase” faces into a 2-sided face, I get this message:
"Error:
Failed: Create 2 sided geometry”

It does not matter which face I try to make 2-sided, I always get the error message. I have ensured that the embedded faces do not already have any BCs or other specifics assigned to them. Do I need to do something different?

Thank you very much for your help.

PeterG

### Create staircase volume with thin thickness

Given the complexity of your staircase geometry, especially the way it connects to the primary volume I don't think double-sided faces will work reliably for your model. Instead I suggest you construct the staircase as a volume with a relatively thin thickness so that you can use standard Boolean operations.

The technique for creating double-sided faces I described requires that they be totally enclosed by the surrounding volume, i.e., no edges touching the outer volume.