脸是没有背的

我有那个代码:

var roofGeometry = new THREE.Geometry();
roofGeometry.vertices.push(
    new THREE.Vector3(-0.5, 0, 0.5),
    new THREE.Vector3(0.5, 0, 0.5),
    new THREE.Vector3(0, 1, 0.5),
    new THREE.Vector3(0.5, 0, -0.5),
    new THREE.Vector3(0, 1, -0.5),
    new THREE.Vector3(-0.5, 0, -0.5)
);
roofGeometry.faces.push(
    new THREE.Face3(0, 1, 2),
    //new THREE.Face4(1, 3, 4, 2),
    new THREE.Face3(5, 3, 4)/*,
    new THREE.Face4(0, 5, 4, 2)*/
);
//...

为什么当我旋转三角形时它们消失了?