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Community and Q&A

Sealing an Exterior Outlet

pico_project | Posted in General Questions on

Is this what I want to properly seal up an exterior outlet with new Hardie Board lap siding?

I bought one to check it out and the flang seems pretty thick. It also doesn’t mention rigid siding on the box (only stucco and masonry surfaces).

I’m looking for something that looks good and can be taped at the sheathing. This seems to be the closest to that, but rather thick. Concerned the siding will bulge around it.


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  1. Expert Member
    BILL WICHERS | | #1

    I would trim around the outlet with PVC trim, then tie the hardiplank (I think that's probably what you're using) into that in the usual way just as you would at a door or window opening. You don't really need a fancy box. If you use the PVC trimboard to bring the face of the box out, you can use a regular cover on the box (which usually means an "in-use" cover these days). The trim board creates a flat surface for the cover to seal against, then you mount the box against the sheathing or on blocking if needed to get everything to align correctly. I've never used any special boxes myself.

    I don't like the specific box you show because the lid/cover is part of the assembly mounted within the wall. This means you can't replace just the exposed part if it gets damaged in the future. With a regular box, the cover assembly is removeable and seperate from the electrical box that mounts within the wall, so if something happens to damage the cover it's a simple job to install a new one without having to open up the wall.


  2. Expert Member
    NICK KEENAN | | #2

    I would take a piece of the trim you're using for cornerboards and around windows and cut a rectangle about 6" wide and tall enough so the ends fall on the courses of siding. I'd flash it at the top like a window top, z-flashing and adhesive flashing, except I'd leave the Tyvek uncut behind it and just slit it at the top so the flashing toes under. I'd drill a half inch hole in it, run the romex through the hole and put a surface mount exterior box there with the romex entering from the back. Then I'd fill the hole the romex was in with silicone.

    Trying to flush mount is going to make a hole in your house in a bad spot. You can surface mount to the Hardie, but doing the mounting plate gives the best reliability.

  3. Expert Member


    Buy a siding mounting block at one of the big box stores. They are a pre-made version of what Bill and DC are suggesting. Use the same ones for hose-bibs and any other small exterior penetrations for a consistent look.

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