HOT TUB - gut check 1

[Ben29]

I am supporting a hot tub on an elevated wood framed deck. The deck joist will be supported via a top flange hanger attached to a nailer on a steel beam. I wish I could bear the wood joist directly on top of the beam, but I cannot for architectural reasons. I am concerned about the top flange hanger rusting out and failing over time. I am specifying simpson model WP with HDG finish and Type 316 Stainless Steel nails in all holes.

Should I be concerned about this?

 

[XR250]

I'd be more concerned about the eccentric load on the beam if there is any.

 

[phamENG]

Use HDG or Stainless. Don't mix them. Zinc and Stainless are very reactive and galvanic corrosion will eat those nails.

 

[ANE91]

I remember watching some webinar recently discussing what it would take to completely protect the deck members and fasteners from this type of corrosion. The consensus was a veritable jungle of flashing details that would be completely impractical. Even if you use zinc-magnesium hangers or stainless steel hangers, what about the beam? What about when the wood rots out, first? A design like this doesn’t warrant a corrosion consultant. Follow AWC’s deck guide and don’t mix metals. Good luck!

 

[Tomfh]

Don’t mix metals.

 

[Harbringer80]

Use both HDG fasteners and nails. Then sleep like a baby.

I'd be more likely to specify galvanized flashing cap over the nailer or more like specify the hanger to be welded on the beam before being HDG.

You are overthinking this.

 

[Eng16080]

Hopefully the beam is also HDG. I don't think I'd be overly concerned with an HDG beam, PT nailer on top, with all HDG top flange connectors and hardware.

If I was worried about a thin Simpson top flange hanger rusting and failing, I might consider fabricating connectors from 1/4" steel plates shop welded to the beam prior to galvanizing (like Harbringer mentions). This seems somewhat overkill though.

You could also use an alternative connection detail with the joists bearing on the inside of the beam bottom flange. This assumes the beam (and end connections) can handle the torsion (although maybe it's no worse than the top flange connection anyway).

 

[XR250]

You could also use an alternative connection detail with the joists bearing on the inside of the beam bottom flange. This assumes the beam (and end connections) can handle the torsion (although maybe it's no worse than the top flange connection anyway).

We still don't know if this is a one-sided connection to the beam or not. If it is, I'd be packing out the beam and using hangers to gain at least a bit of torsional resistance. This was recently discussed.

 

[Eng16080]

We still don't know if this is a one-sided connection to the beam or not. If it is, I'd be packing out the beam and using hangers to gain at least a bit of torsional resistance. This was recently discussed.

This isn't a detail I use often (bearing the joist on the beam btm flange), although I think this would induce less torsion than packing out the beam web since the eccentricity from the joist would be a little less.

Regardless, it would be better to make this a two-sided connection. Even if the loads from both sides are unbalanced, there would be more torsional resistance since the beam would be more locked into the floor.

 

[XR250]

This isn't a detail I use often (bearing the joist on the beam btm flange), although I think this would induce less torsion than packing out the beam web since the eccentricity from the joist would be a little less.

Regardless, it would be better to make this a two-sided connection. Even if the loads from both sides are unbalanced, there would be more torsional resistance since the beam would be more locked into the floor.

Would you be relying on friction only or would you have a nailer bolted to the bottom flange?

 

[Eng16080]

Would you be relying on friction only or would you have a nailer bolted to the bottom flange?

The detail specifics would depend on OPs conditions, although I wouldn't be relying only on friction. I was picturing a web nailer bolted to the steel beam and connected to the end of the joist with a Simpson angle. The bottom of the joist would be bearing directly on the bottom flange.

 

[Harbringer80]

Hopefully the beam is also HDG. I don't think I'd be overly concerned with an HDG beam, PT nailer on top, with all HDG top flange connectors and hardware.

If I was worried about a thin Simpson top flange hanger rusting and failing, I might consider fabricating connectors from 1/4" steel plates shop welded to the beam prior to galvanizing (like Harbringer mentions). This seems somewhat overkill though.

You could also use an alternative connection detail with the joists bearing on the inside of the beam bottom flange. This assumes the beam (and end connections) can handle the torsion (although maybe it's no worse than the top flange connection anyway).

No need to have a custom hanger. Many of Simpson's light gauge top flange hangers can be welded directly to the beam. Image shows an IJ but you get the idea for solid sawn PT lumber.

 

[jerseyshore]

As others have said, spec the steel beam and all connectors galvanized or stainless, don't mix.

I like the idea of welding the hangers directly to the top flange of the beam, but they aren't going to like field welding to galvanized steel a bunch of times.

I'd prefer adding PT blocking in the webs and face-mount hangers. Then you get to load up the hangers with galvanized nails/ screws and you'd also have the toenails the framers install during construction as a bit of a backup when the hangers inevitably rust out. Adding some sort of 1x or 2x ledger (or bottom flange plate) to the bottom can give you some more confidence with a bearing condition if you want.

 

[Flotsam7018]

Zinc and Stainless are very reactive and galvanic corrosion will eat those nails.

Nope, the hanger is the anode in this scenario. My understanding is that if the cathode to anode ratio is small, such as the case with an HDG hanger and stainless nails, you’re not going to rust out the hanger unless in an extreme environment. If the materials were reversed, yeah - bad news.

 

[gte447f]

Nope, the hanger is the anode in this scenario. My understanding is that if the cathode to anode ratio is small, such as the case with an HDG hanger and stainless nails, you’re not going to rust out the hanger unless in an extreme environment. If the materials were reversed, yeah - bad news.

You may well be right, but just don't mix the materials seems like better advice.

Reality check for this entire thread, go with hot dip galvanized and forget about stainless steel. HDG has worked just fine for forever and it's probably about 1/4 of the cost of stainless steel (nails). For the record, I have never in my life seen a stainless steel nail in the wild. In my opinion, there is no reason to specify stainless steel in common construction.

 

[gte447f]

I was picturing a web nailer bolted to the steel beam and connected to the end of the joist with a Simpson angle.

Seriously? Have you ever actually used this detail or did you just throw that out on the fly? That's a lot of fabrication to achieve very little.

 

[Eng16080]

No need to have a custom hanger. Many of Simpson's light gauge top flange hangers can be welded directly to the beam. Image shows an IJ but you get the idea for solid sawn PT lumber.

I brought up the custom hanger idea because OP was concerned about the light gauge Simpson connector rusting through. With a 1/4" thick fabricated connector, if it were to rust, it would take a very long time before the strength would be diminished enough to be an issue. I recognize this is likely way overkill.

I've specified Simpson connectors to be welded to steel a few times. I'm not entirely on board with this approach. For one, the steel fabricator often struggles with this (dealing with shitty fabricators is to some extent the problem). I've required shop welding and often this gets missed. Welding the thin gauge metal can be a problem. Also, if the connector is galvanized, the zinc coating will need to be removed in order to weld, and then how is it being protected from corrosion?

 

[phamENG]

Nope, the hanger is the anode in this scenario.

Good call. I flipped them around. Even so, I wouldn't mess with it. Under a hot tub could well be considered an extreme environment. Chlorine treatment in hot tubs is very common, and water splashes out and around all the time. Now if just sits there and is never used, maybe not a problem. But I wouldn't want to count on that.

Most hot tubs on decks near me are also along the coast, so I usually assume a marine or near marine environment anyway.

go with hot dip galvanized and forget about stainless steel.

Not always a great option, especially in marine or near marine environments. North Carolina has rules for its beach communities that require any steel connector thinner than 3/16" to be stainless, while anything larger can be hot dip galvanized. Looked at a house out there a while back and it's obvious why that is. House was only about 20 years old, and I could brush away what was left of the HDG simpson hangers on the porch and under the house with my finger. I think Simpson might make some specialty hangers for these environments, but for the thin stuff stainless is best in severe cases.

 

[gte447f]

Not always a great option, especially in marine or near marine environments. North Carolina has rules for its beach communities that require any steel connector thinner than 3/16" to be stainless, while anything larger can be hot dip galvanized. Looked at a house out there a while back and it's obvious why that is. House was only about 20 years old, and I could brush away what was left of the HDG simpson hangers on the porch and under the house with my finger. I think Simpson might make some specialty hangers for these environments, but for the thin stuff stainless is best in severe cases.

OK, I'll give you that one. Coastal and certainly marine environments are a severe exposure category, so a special case where special materials like stainless steel would be appropriate.

 

[jerseyshore]

OK, I'll give you that one. Coastal and certainly marine environments are a severe exposure category, so a special case where special materials like stainless steel would be appropriate.

NJ also requires stainless steel connectors and fasteners within 300 ft of saltwater. Simpson guys are making $$$ down here.