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We're getting a sliding door and deck installed this week and the town inspector said I need to have an outside light by the door. I'm ready to tackle this part myself. Most of the howto stuff I find online says "It's easy, just remove the existing light fixture..." and I have no existing light fixture.

Do I need to cut a large hole in the aluminum siding and mount an outlet box to attach the fixture to? If so, how do I secure it?

Or is there a very low-profile outlet box I can put flush to the siding that won't stick out too much and won't require a huge hole?

Some of the fixtures in my house (not sure about the outdoor ones) have been installed without boxes altogether. I'm guessing this is not code, and I'm further guessing this is a corner that one shouldn't cut for outdoor lighting. Especially since the wall cavity has blown-in cellulose insulation--I feel like I should avoid having splices in contact with that.

Edit Thanks for the help. In the end I went with the large hole and retrofit light box.

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up vote 10 down vote accepted

Electrical code requires that all junctions be accessible in a box, so you definitely need one here. You have two choices (that I know of at least):

remodel box

  • drill a small hole in your siding and mount one a weatherproof box on the outside:

exterior box

The exterior boxes come in a range of depths and colors so you should be able to find one you like.

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Is the retrofit light box shown OK for outside use? – Vebjorn Ljosa Nov 11 '10 at 15:27
@vebjorn: one of my wiring books shows one being used in an exterior location with a rubber gasket (supposed to come with the light) and a grounding clip on the box if the light fixture doesn't have a grounding stud. Are you concerned about water getting into the wall cavity? – Niall C. Nov 13 '10 at 14:59
Yes, I am concerned about water getting into the wall cavity. – Vebjorn Ljosa Nov 14 '10 at 11:01
FWIW, I caulked around the fixture where it contacts the wall. – Matthew Leingang Dec 3 '10 at 1:10

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