problem with subsurf

Hello everybody

Can someone explain me why when i apply a subsurf to this mesh i’m geting this distortion :

Hi mrfranz, and welcome to elysiun! I’m still a newb in a lot of ways, but your problem might be that you need to recalculate the normals. Go into edit mode (tab) and select all of the vertices (ctrl + a), then recalculate the normals.(ctrl + n) Hopefully that will fix it.

Thanks a lot, It worked fine !