Mesh Geometry not getting rendered properly after flipping the orientation

Im trying to create a mesh geometry from another software whose co-ordinate system is Y-up.
When i try to create the meshes i had to flip the vertex as shown in below code

FVector vec = FVector(x, z, y);
instead of
FVector vec = FVector(x, y, z);

But only the inner surfaces are rendered as shown in the attachment.

Can anyone help on fixing this ?

Also what is the minimum data like (VertexPositions,WedgeIndices,WedgeTangentX,WedgeTangentY,WedgeTangentZ
) is required to render complete and perfect model in UE ?

What is causing this problem ??

Thanks in advance


The coordinate system shouldn’t matter in normals! All would happen is that the WHOLE MESH would be tilted by 90 degrees.
You should flip the “faces” (normals) of your mesh in your 3d app!
…you can try two sided material in Unreal…

Thanks @Makigirl for the suggestion, lot of people on internet suggesting that, but inverting z coordinate worked for me.