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Community and Q&A

Grounding a Steel Deck Frame

David Williams | Posted in General Questions on

I’m building a weekend cabin designed along the lines of a fire lookout tower. As I am in an wooded area with high potential for wildfires, I am trying to use materials which minimize fire risk. The building footprint is a 22′ square and will be constructed using Faswall blocks covered with steel siding and a steel roof. The upper level will have a wraparound “catwalk”-style deck about 15′ above ground level. The deck frame will be constructed of hollow structural steel supported by braces anchored to the building walls and the actual decking while probably be a composite decking material.

Should the deck frame be independently grounded? The building site is on a hill and exposed. And I have read comments by several homeowners who have complained of static buildup from composite decking, causing frequent uncomfortable shocks. Is there a way to eliminate or minimize this type of problem?

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    It seems you have two issues: First, how best to ground the structure’s electrical infrastructure. Second, whether to protect the structure and its occupants from lightning ground strikes. Would you agree?

  2. David Williams | | #2

    No. While you raise legitimate concerns, I see them both as independent of the questions I asked in my original post. The electrical system for the cabin will be grounded according to code, with two grounding rods at the meter and two grounding rods at the cabin and tied into the main service panel. As for lightning protection, I am looking into installing lightning rods on the cabin roof with a separate grounding rod.

    The elevated deck structure is essentially a floating steel ring around the outside of the cabin and I don't know whether it would make sense to tie it into the lightning rod grounding path or not. As for the static issue related to the composite decking, I see that as another separate issue.

  3. Expert Member
    Malcolm Taylor | | #3

    David,

    I don't think grounding the metal structure will help. Plastic decking isn't conductive - and it isn't charged. The charge is generated by the friction between dust and your shoes, and discharged when you touch a conductor, like a door knob or railing.

    I understand they sell anti-static coating for the decking if it is a problem.

    BTW, it sounds like a neat building!

  4. Expert Member
    Dana Dorsett | | #4

    How fire resistant is composite decking?

    With fire towers all structural metal and grounding schemes need to be reviewed and consistent with the lighting protection design.

  5. David Williams | | #5

    Can someone direct me to a reputable company which sells lightning rods and could provide me with some guidance on designing and installing lightning protection for my structure?

  6. Andrew Bater | | #6

    I believe lightning protection systems to be one of those areas where it's advised to use a vendor who can do the project turnkey. This work is (in my view) 50% adherence to standards/recommended practices, 40% contractor experience, and 10% black magic. So your contractor/supplier request likely needs to be geographically focused.

    This is the company that installed the lightning rods/system in my barn that sits atop a promontory/bluff here in Central Pennsylvania: http://teateslightning.com/index.html

    You can see on their website that the folks at Teates are members of two different trade associations, the Lightning Protection Institute (http://lightning.org) and the United Lightning Protection Association (http://www.ulpa.org) so those are probably good resources to find similar contractors in your area.

    You might also want to review the National Fire Protection Association standards for lightning protection: http://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=780

  7. David Williams | | #7

    Thanks, Andrew, for the site links.

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