Hi
So, I’ve got a simple shape, a hollow rectangular prism, i.e. a 3D rectangle , but only 4 walls top,bottom, right and left,a d you can look though from front to back. I need the length to increase by 28mm. One way is I can click on left outside wall and pull 28mm, then select left inner wall and push 28mm.
Is there away I can do this in one simpler step?
Hi - would you be able to provide a picture or some visual aid?
If the shape is this simple, I would extrude the selected wall, and then subtract the unnecessary extruded mass with simple push pull subtract from the inner side.
I have also seen users who have split the body into parts (by creating copies and subtracting) and then connected them in the desired why by extruding.
Hope this helps. Picture would give me a better idea about your exact problem 
What about as in Onshape, an ability to stretch a surface and copy as a new solid? Feature being a Copy toggle!
It’s just not recognizing boundaries in the same way, I have to set new sketch.