Three.js Simulate Floor Reflection

Objective :

I want to simulate a reflective floor (like this) in three.js

Also, I don't want to duplicate the house and make a transparent floor as that increases the size of the model.

I tried setting up a cubeCamera and rendered its output to floor but it always shows black.

        mirrorCamera = new THREE.CubeCamera(0.01, 1000, 512);
        mirrorCamera.renderTarget.minFilter = THREE.LinearMipMapLinearFilter;
        scene.add(mirrorCamera);

        var mirrorFloorMaterial = new THREE.MeshLambertMaterial(
                    {
                        map: floorTexture,
                        reflectivity: .8,
                        side: THREE.DoubleSide,
                        envMap: mirrorCamera.renderTarget
                    });

        mirrorFloor = new THREE.Mesh(cubeGeom, mirrorFloorMaterial);

        mirrorFloor.doubleSided = true;
        mirrorCamera.position = mirrorFloor.position;

        scene.add(mirrorFloor);
        ......
        ......
        //in render()

        mirrorFloor.visible = false;
        mirrorCamera.updateCubeMap(renderer, scene);
        mirrorFloor.visible = true;

        renderer.render(scene, firstPerson.camera);

Questions:

1) Why do I always see black in place of floor and not what cubeCamera should have rendered?

2) Can anyone suggest a neat way to simulate floor reflections?

Thanks in advance.