I'm trying to install a ceiling light in two rooms that didn't previously have hard-wired lighting. After cutting a 4" hole for a circular ceiling box (using a hole saw attached to my drill) I'm finding that the ceiling box I've got might not fit:
The problem is that the ceiling is too thick. There is the original plaster & lath ceiling, and below that another layer of strapping and a fiberboard ceiling. All together, the thickness is 3 or 4". If I set the ceiling box in the hole from the attic, it sits very far from the ceiling surface you'd see from the room below. Because of the distance, I don't think it would be possible to mount a light fixture there.
So, how do I mount a ceiling box in this deep/thick ceiling? Is there a special box (or extension?) for situations like this? Do I need to somehow remove some of the upper layer of old ceiling in order to reduce the depth? Any special concerns for supporting the box?
Best Answer
I agree with answer #1 with the following exception: Do not use longer screws to attach the fixture. Find a suitable box with extensions as needed to make the box opening flush with the ceiling surface. You do not want a gap between the box and fixture the could allow heat and spark from a fault in the box to escape. Here are products that I would use in your situation. These may not be available at home improvement store but are available at electrical suppliers who service contractors.
For support between studs -- Erico/Caddy TSGB24 or simply use a 2x4
Box attached to support --4" octogon box
Two extension boxes as need to bring opening flush -- 4" octogon extension box 2 1/8" deep
This combination gives you a box 5 3/4" deep. Adjust the support on the attic studs to make this flush with ceiling.
Remember that it is important to not leave a gap that could cause a smoldering fire in the voids of the ceiling structure. This is the reason that most electrical codes require that box faces be flush with the finished surface.