Stack A Cube Over Another Dynamically

I am working on a project in three.js, where the user can change dynamically the dimension of the objects inside it. The objects are two boxes with different dimensions and one box

Solution 1:

Here is one solution:

    cubeY.onChange(function(value){
        cube.scale.y = value;
        cube.position.y = (cubeHeight * value) / 2;
        chimney.position.y = (chimneyHeight * chimney.scale.y) / 2 + cube.position.y * 2
    });

    chimneyY.onChange(function(value){
        chimney.scale.y = value;
        chimney.position.y = (chimneyHeight * value) / 2 + cube.position.y * 2;
    });

and here is fiddle for it: http://jsfiddle.net/z1yd342b/

three.js r71