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I am planning to run 1-1/4" black iron natural gas pipe around the outside of my house to supply an exterior tankless heater. The pipe needs to be attached to the wall and I'm planning to use two-screw metal hangers driven through the stucco into the studs underneath. I had a local plumber suggest using 2-1/2" deck screws for this purpose, but deck screws have no shear strength and are emphatically not structural screws. This plumber has repeatedly demonstrated a lack of knowledge of plumbing codes in California, so am pretty sure that deck screws are precisely the wrong thing to use. What kind of screws are the correct ones to use (that is, will keep the building inspector happy)? I couldn't find anything specifically called out anywhere and I would really like the pipe to not fall off the wall unexpectedly.

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  • I had a building inspector out at the house for another inspection today and asked him questions about the pipe. He said absolutely not for deck screws or drywall screws or drywall anchors to attach pipe to stucco using two hole straps. He also said that the inspector can't specify the screws to use, but that they should be structural ones in this case. Being familiar with the work of the plumber who gave me the advice on what screws to use, he also suggested that I use the proper-sized straps and not try hanging pipe with plumbing strap or poly rope as a way to attach the pipe to the wall.
    – Joseph
    Commented Apr 4 at 15:21
  • The inspector also said that the local building department recommends strongly against using galvanized pipe for exterior natural gas because galvanized pipe reacts with the natural gas in the lines over time and reduces the service life of the pipe. He said that they are expecting to see black iron pipe painted with anti-rust paint for this kind of use. Maybe it's just a local thing?
    – Joseph
    Commented Apr 4 at 15:24
  • I'm still hoping to find out which screws i should use instead of just finding out which ones I shouldn't use. I do appreciate you taking the time to offer advice, btw.
    – Joseph
    Commented Apr 5 at 20:50

2 Answers 2

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I asked several other plumbers what they do and I asked the local building department (not just the inspector) what they recommend and it looks like the preferred method in my local jurisdiction is to use two-hole metal straps of the appropriate size attached through the stucco into the stud below using at least 2" long #12 structural screws with pan heads (at least an inch into the stud after the stucco). Pre-drill the stucco with a masonry bit to avoid damaging the screws and fill the hole with caulk before driving the screws into the stud to prevent leaks. An explanation given for the overkill is that children and drunk adults find climbing on and hanging from the pipes almost irresistible and it's better to spend a few extra dollars up front than to have everything yanked off the wall.

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  • You are allowed to answer your own question. You can even tick it after a day. So, I am removing the first sentence. It adds nothing to the answer. Commented Apr 13 at 19:51
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Deck screws have plenty of shear strength. Heck, even drywall screws do. There's very little shear force involved anyway--sheet metal straps deform enough that most force ends up in tension. I challenge you to pull such a strap off the wall with two screws in it with anything short of a crowbar.

Unless you plan to mount your climbing wall on your gas piping it's not remotely a concern. They're exactly what I'd use (for their corrosion resistance) if I didn't happen to have stainless or coated pan-head screws on hand (and who does?). 2-1/2" seems appropriate assuming ~1-1/4" of stucco and strap.

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  • The problem I've encountered with drywall screws and deck screws is that they are indeed very strong screws, but they are also very brittle. I used some 3" drywall screws that I had on hand to hold up a temporary panel on a hole in my fence during construction. We had a bit of wind (30mph + gusts) and the screws snapped off completely after a couple of days. I probably didn't use enough screws because I wasn't expecting it to be that windy, but it was certainly annoying to see that panel there on the ground and the dogs out in the neighborhood.
    – Joseph
    Commented Apr 4 at 15:30
  • You might've had that problem with steel screws, too. Black oxide screws are harder, but I've probably twisted off as many steel screws as I have snapped off drywall screws.
    – isherwood
    Commented Apr 4 at 16:34

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