Does this happen with all the meshes? I think Stevie is correct in saying you will need to physically make the walls in your modeller. Showing the backfacing triangles will not give them collision properties.
issue with collisions in blitz3d
Blitz3D Forums/Blitz3D Beginners Area/issue with collisions in blitz3dThe forum is locked. These are the original blitzbasic.com forums, kept so they can still be read. No new topics, replies or edits can be made here. To join in, head over to the Blitz3D+ forums.