Drywall Screws in Flush Mount Hanger 4

[zero1238]

Had a client reach out to me about inspecting their house. Supposedly, they have a garage converted into living space but the crawl beneath it is mostly inaccessible. Home inspector saw that many of the joists under there, which look PT from the picture he sent, are flush mounted with steel mounting brackets being attached with drywall screws instead of manufacturer specified fasteners. I see this being an issue for two reasons:
1. Corrosion of steel from the pressure treatment; drywall screws don't have any type of corrosion resistance that I'm aware of.
2. Shear capacity. I know that drywall screws are a lot more brittle in comparison to other typical screws, such as even deck screws. It's hard to find information on their allowable loads.

What are everyone's thoughts on this? Would this be enough to warrant pulling up the floor and replacing all of those fasteners? I should know more once I get out there but trying to do some preliminary research. Image attached:

 

[Eng16080]

Assuming the wood is pressure treated, the joist hangers should be removed and replaced unless they're galvanized or otherwise rated for contact with PT lumber.

Whether the wood is PT or not, drywall screws should not be used unless allowed by the manufacturer. I'm not aware of published design values for drywall screws, but I can say based on my own construction experience that they are very brittle.

Also, if the wood is PT, the fasteners should be suitable for contact with PT lumber (as well as suitable for contact with the joist hanger). In general, don't mix different materials. Even using stainless steel fasteners in contact with a galvanized joist hanger, for example, is not recommended.

A suitable fix would be along the lines of galvanized joist hangers and galvanized fasteners. I think it should be possible to individually remove and replace each connector, meaning that only one joist would be unsupported at it's end at a time. I don't think it's necessary to remove the entire floor (if that's what you meant).

 

[zero1238]

That's exactly what I was thinking. What I meant was that given that there is little to no access underneath, the subfloor will need to be removed in order to replace the necessary fasteners and possibly the hangers. Thank you for your input!

 

[DoubleStud]

I assume the garage elevation is about a foot down and they framed over the slab? Is this an inspection prior purchasing the house? More than likely your recommendation is just being used to lower the price of the house and it will never get fixed. Is the column(s) in the middle supported by a foundation? Or just sit on the garage slab?

 

[jerseyshore]

I'm trying to get a sense of this photo, is this a beam that passes over a wood post that has a smaller joist framing into the side of it? And is the hanger on the beam with one flange on a perpendicular joist and the opposite flange screwed into a different perpendicular joist on the other side? Please tell me I have the perspective wrong.

 

[zero1238]

I haven't physically been there yet, this is just a picture from the inspection report. I'll have more info when I go there on Monday. I'll keep everyone here posted on what I see when I go over there.

 

[msquared48]

The joists do not look pressure treated to me so that should not be an issue.

However, the mounting screws should be removed and replaced with a screw that is recommended by the joist hanger manufacturer. That can be done sequentially to each joist without removing the floor structure as mentioned previously.

Mike McCann, PE, SE (WA)

 

[Eng16080]

It's just a guess of course, but to me the joists do look like PT, or at least Southern Yellow Pine. Tough to tell from a picture, of course. Looks about like what we use here in the Northeast for PT, once it's dried out a bit.

 

[jerseyshore]

I really do hope that they installed the hangers on the wrong piece, that would be a hilarious blunder, but 100% on par with what you would expect with someone using drywall screws.

 

[lexpatrie]

The other issue is the drywall screw, besides not being rated in the hanger for that application, may not have the necessary length, even if you're going to authorize it, and the screw might have damaged the connector, to say nothing of the potential corrosion issues and the incompatibility with the pressure preservative treated wood (PPT NOT PT). The wood doesn't look incised, so if it is PPT it's likely SP.

I don't think you can just "fix" the connection without checking the framing as well. I know it's tempting.

 

[MintJulep]

Drywall screws are simply not ok for this.

Additionally, if the joists are PT, then they will corrode to nothing in a few years.

 

[zero1238]

Update after seeing the house: The joists are pressure treated and the screws are drywall screws. Not good!

 

[Enable]

Just as FYI if you replace screws they need to be of a larger diameter than those you remove. If they are close to what is there they won't achieve the rated capacity as a result of the existing wood already being torn up at the thread location. Since you're replacing drywall screws and you're probably going back with some sort of rated simpson strong-tie fastener it shouldn't be an issue though.

 

[zero1238]

Good call, thank you.

 

[jerseyshore]

Were the hangers "traditionally" installed (wrong screws obviously) or were there some weird connections on this?

 

[zero1238]

They look to be traditionally installed, at least from what I could see (couldn’t fit in the 8” of clearance beneath the floor. It looked like primarily a fastener issue.

 

[Canuck65]

The capacity of drywall screws in this application is zero.

If it is a Simpsons Strong-Tie hanger, look up the model in their catalogue and it will tell you the proper fasteners to use. Then you will need to evaluate the effect of the existing holes, hopefully the nails specified will have a larger diameter than the drywall screws.

 

[Eng16080]

While you're at it, also check that the joist hangers are rated for contact with pressure treated lumber.