Trouble capping planar brep

HI There,

Was wondering if there is a simple solution or answer to why some planar breps dont close in rhinocommon but will close manually.

Here is the code for the class - function.

//function to extrude in world z axis segmentstojoin by height
        public static Brep[] extrudeedgebeam(Curve[] segmentstojoin, double height)
        {

            //create brep array
            Brep[] extrudededgebeam = new Brep[segmentstojoin.Length];

            
            //loop through segmentstojoin and extrude
            for (int i = 0; i < segmentstojoin.Length; i++)
            {
                //find bbox centre point of segmentstojoin
                BoundingBox bbox = segmentstojoin[i].GetBoundingBox(true);
                Point3d centrepoint = bbox.Center;

                //new curve duplciate of segmentstojoin
                Curve newcurve = segmentstojoin[i].DuplicateCurve();

                //move segmentstojoin in world z axis by height
                newcurve.Translate(new Vector3d(0, 0, height));

                //create new point moved in world z axis by height
                Point3d newpoint = centrepoint + new Vector3d(0, 0, height);

                //extrude segmentstojoin
                extrudededgebeam[i] = Brep.CreateFromLoft(new Curve[] { segmentstojoin[i], newcurve }, Point3d.Unset, Point3d.Unset, LoftType.Tight, false)[0];

                //move in z axis by - half height
                extrudededgebeam[i].Translate(new Vector3d(0, 0, -height / 2));

                //create surface from newcurve
                Surface newSurface = Surface.CreateExtrusion(newcurve, new Vector3d(0, 0, 1));

                //create surface from segmentstojoin[i]
                Surface newSurface2 = Surface.CreateExtrusion(segmentstojoin[i], new Vector3d(0, 0, 1));

                //join extrudededgbeam[i] and newsurface1 and newsurface2
                Brep[] joinedbreps = Brep.JoinBreps(new Brep[] { extrudededgebeam[i], newSurface.ToBrep(), newSurface2.ToBrep() }, 0.01);

                //add joinedbreps[0] to extrudeedgebeam
                extrudededgebeam[i] = joinedbreps[0];


            }


            return extrudededgebeam;
        }

Noting I tried close planar and didnt work. So started to try making individual surfaces from top and bottom and join back together. Individual surface dont work either.

Please note I am a noob.

thanks for your help.

I’ve not looked deeper into this, but it seems only the cornered breps are not capped. the most common error with cap is that the borders are not planar.