I’d like to add a light fixture to the outside of my house.

The exterior wall is constructed as follows: there is plywood sheathing on the studs, on top of that sheathing is hard foam insulation, on top of that insulation are 1”x 3” vertical nailers 16” on center, on top of those nailers is attached the horizontal wood siding. Thus, there is a vertical chase behind the siding every 16”.

I have an existing exterior outlet that is recessed into the wood siding.

Starting at the existing outlet box, can run a piece of UF-B cable up though the 3/4” chase (between the wood siding and the foam insulation) to a new weatherproof box to be located under the soffit for the light fixture? Or, I have to run conduit on top of the siding between the boxes?

  • Where exactly do you live? Some jurisdictions require conduit
    – DoxyLover
    Sep 27, 2020 at 23:28

3 Answers 3


As far as the NEC code is concerned You can run the UF in the void between the furring strips it sounds like you will be fishing the wire into the void. If you have to remove the siding to put it in staple your wire 1-1/4 inch away Or more from the furring strip. Exhibit 300.2 has a good example of this. Some areas do require conduit Chicago just about everything requires conduit or metal clad. But by the standard code UF would be allowed unless additional requirements mandate conduit.


MC cable would provide a little more protection, but I agree that UF is o.k. (in most localities).


You can use exterior wire with zero issues. Long term conduit is recommended but not necessarily needed and with new low pull fixtures you can use really easily handled wire.
Lighting expert with decade of installs TNJR

  • 1
    Many areas require conduit for all wiring.
    – JACK
    Sep 28, 2020 at 1:18

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