Situation: Want to install lights/lanterns on both sides of an entry door. Exterior surface is fiber cement siding.

Want to make an "offset" on the siding to make the light mount level. The siding has an angle, and making up for the difference in slant of the siding.

Question: Do I mount the "light outlet box" from the interior to flush with the surface of the sheathing? I guess the answer would also apply with the boxes that hold the exterior outlets.

The interior outlet boxes are flush with what should be the drywall, and it does make sense to me that the box for the lights would be flush with the exterior portion of the sheathing since the inspector would typically approve a light box during the framing inspection before any siding was installed.

 

Take a look at the following Arlington Industries products.
The block with integral electrical box might be the way to go.

http://70.86.88.179/k_1.htm

http://70.86.88.179/whnew24.htm

http://70.86.88.179/arliprod6.htm

 

With the product shown in the first link above you would still need to install a pancake box and have to watch how many wires in each box.

I much prefer the products like in the second link that contain a built-in junction box.

 

Just a quick safety note if this is existing construction. Old fiber cement siding material often contains asbestos so be mindful of dust when cutting or drilling.

Usually the exterior box is mounted flush to the sheathing material then a siding block with box extender is installed to reach the final finish. The Arlington products mentioned above are very good for this purpose.

Some people may also choose to fabricate a mounting base for the light out of wood which is okay as long as you use a box extender through the wood or simply forgo the wall box and install a pancake box on top of the mounting block with a hole bored through the wall for the cable.