Joist hangars and drywall screws

[jar546]

Does anyone else have this happening all the time? Simpson and USP don't give you and option for drywall screws on joist hangars. Not many screws are approved for this to begin with.

 

[KZQuixote]

Treated wood and black screws, not a winning combination.

I've used plenty of 1 5/8" corrosion resistant deck screws in similar locations. I realize that they're not approved either but the inspectors I've worked with around here realize how strong the deck screws are and have not called me on them.

Bill

 

[steveray]

All over here...."but the screws hold better"....yeah...but did you ever snap one? Is usually my question back...

 

[fatboy]

Not "did you", but how often do you? Not very much for sheer, not an engineering opinion, but........they sure do snap easily. Not acceptable here.........

 

[Mark K]

Tell them to either remove the drywall screws or have an engineer calculate if there is enough capacity for the existing screws. I believe that Simpson now has some provisions for screws in joist hangers.

 

[texas transplant]

Until I see an engineers detail, manufacturers report or something, no screws here. I do not feel they are the same in shear strength as a nail. And when asked about it, no one has found any info to prove me wrong. I wish there was something like that though, seems in a lot of instances the install would be easier and as stated above, screws tend to not pull out as easy as a nail.

 

[Glennman CBO]

Not here.

Correction... Provide hanger manufacturer's approval.

Simpson has a screw for this. It's either the approved nail size, or manufacturer approved screw.

Is that joist spliced (where you can see the nails in the side of the joist)?

 

[FredK]

Only if they look like this: http://www.strongtie.com/ftp/catalogs/c-2011/C-2011-p028.pdf or http://www.strongtie.com/ftp/catalogs/c-2011/C-2011-p029-p030.pdf

 

[cboboggs]

Not allowed here either.

 

[High Desert]

Not only no, but hell no.

 

[rktect 1]

Is this a serious question?

I'm having a hard time believing this is acceptable somewhere.

 

[steveray]

Is this a serious question?I'm having a hard time believing this is acceptable somewhere.

Not acceptable....but far too common....last town I worked in had alot of retired engineers from Prat and Whitney....had too explain this a bunch...

 

[dhengr]

Jar:

There are a number of things wrong with your picture, the primary one being that SIMPSON and USP will not stand behind their products used that way. They have no rated load values or testing for that installation with those screws. The joist hanger manufacturer’s catalog and its pages of general information, along with load tables and all of the foot notes should be required reading before these highly engineered and highly misunderstood products are misused by just any dummy.

Sheet rock screws are hard and do break easily in that application. They corrode very quickly in any wet/damp application, and doubly so in today’s treated lumber. The treated lumber and connector corrosion problem really got all screwed up a few years ago when some people started worrying that some kid might eat a whole playground’s worth of CCA treated lumber, in one sitting, and get arsenic poisoning. So the industry had to switch treatment processes and low-and-behold they switched to treatment products which causes serious corrosion problems with connectors and fasteners. They are still sorting this out, for lack of sufficient history with various treatment methods and products. Finally, sht.rk. screws do not have the proper head, shank diameter, or length for these applications.

Joist hangers and their fasteners basically work in shear (lateral loading) btwn. the hanger and the nail shank, and btwn. the nail and the wood. Thus the shank diameter is all important in terms of its shear area of the fastener and bearing area btwn. the nail and the hanger material; and the nail and the wood in terms of bearing area and the way the nail starts to bend, as a cantilever in the wood, to bring the bearing into play. The nail length is not unimportant, but it is less important as long as it is sufficient to allow this lateral loading, because the issue here is not nail pull out, it’s a shearing (lateral) loading. Therefore, in the tables you will see, 10d or 16d nails of several different lengths depending upon the exact detail, and the correct shank diameter is the important dimension; along with the allowable stress of the fastener, which is generally not the controlling factor. The various hangers are tested using the exact nails called for to establish the load tables. The manufacturer’s intent is to fill the holes, in diameter, with the fasteners; and then to compare the nail strength to the hanger thickness as they study each hanger’s failure mode at a given load.

If I’m reading your picture right, those hangers are called Double Shear Face Mounted Joist Hangers, because the angled side nails have one shear plane btwn. the side of the hanger and the jst. and another shear plane btwn. the end of the jst. and the ledger or rim jst. And, that will increase the allowable end reaction for the jst. I’m having a little trouble with the scale in the picture and am not sure if the jsts. are 2x6's or 2x8's. and it appears that they may have missed filling the top hole into the rim jst., through the hanger wings. The sht.rk. screws are absolutely wrong for this application and the other important thing for you is that that particular hanger, with the proper fasteners, has an adequate capacity for the particular jst. loading.

 

[TimNY]

I usually see the ceramic coated square-head deck screws. I try to explain tension vs shear.. Run about 50/50 with contractors understanding.Simpson guide has a picture of a screw with a "No" (aka Ghostbuster) symbol across it. Below it says, "Screws may NOT be used to replace nails in hangers"Directions... pfft.

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[Architect1281]

Agree TimNY

When ALL Else Fails "Read the instructions"

see this too often

approve at inspection - never

 

[Jobsaver]

At least this problem is easy to fix as the screws are easy to remove and replace with the correct nail. What about the circumstance where hangers are installed using the wrong nail, say a 10cc sinker, or worse, 8d ringshank (very difficult to remove). For a fix, is it acceptable to drill new holes in hangers and install the appropriate number of correct nails?

 

[Yankee]

At least this problem is easy to fix as the screws are easy to remove and replace with the correct nail. What about the circumstance where hangers are installed using the wrong nail, say a 10cc sinker, or worse, 8d ringshank (very difficult to remove). For a fix, is it acceptable to drill new holes in hangers and install the appropriate number of correct nails?

no, and no no. Thou shalt not field-modify engineered products. With engineers stamp, ok.

 

[TimNY]

"Do not add fastener holes or otherwise modify Simpson Strong-Tie Company Inc. products. The performance of modified products may be substantially weakened. Simpson Strong-Tie will not warrant or guarantee the performance of such modified products."

So, adding holes is not an option.

However, if you look at the Simpson manual, there is a section titled "Nail Design Information". In that section there is a table titled "Load Adjustment Factors for Optional Nails Used with Face Mount Hangers and Straight Straps" which will give you load adjustment values if a different nail is used. It's not going to cover a 8d sinker used where a 16d common is required, but it will handle minor variations like a 10d common used where a 16d common is specified.

 

[GHRoberts]

You can look up the strength of the screws in the NDS for Wood Construction and compare that to the of mails from the same document.

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It appears to not be legal for a manufacturer to approve only their own screws.

 

[Glennman CBO]

No modifying of hangers without manufacturer approval, which they will not approve, nor will most builders even go there.

It is easier to replace the screws with approved fasteners in the same holes (at least it is for me to say it).

 

[DRP]

Read footnote 2 in the NDS under wood screws... ASTM A 653, grade 33 steel and then lists bending yield strengths required. This is the old soft wood screw that the head stripped out before you got it driven. They are ductile and will bend like a nail rather than snapping like a drywall OR deck screw, that wasn't a recommendation, don't use those unless you see the designation listed on the box, which it isn't. A field demonstration might be to drive a nail and a hardened screw halfway into a dense piece of wood and then whack it sideways hard. The screw will likely fail, the nail will bend but hold. This is the difference between a ductile failure that screams in warning and a brittle failure that gives none. Since Simpson hangers are a proprietary engineered product I do believe they can list approved screws that have been tested to give tabulated results.

I had a helper that thought screwing toeboards to the roof was a great idea, till he went rattling down by the dormer, screw sheared. I've had decking with juvenile wood shrink lengthwise and shear coated deck screws off.

 

[mark handler]

Most, not all drywall screws are hardened steel, if I remember from my college days, most 8d wood screws”not drywall" screws have a 80 lb shear. The courser the thread, the less shear

#8 DRYWALL SCREW. Diameter of #8 screw is 5/32 inch at shank and 7/64 inch at root , root governs.7/64 inch = 0.1094 about 12 gauge which is 0.1046 and that puts it at or 6d (11.5 ga). The length of a 6d is 2 inches smaller It like nailing with a 6d nail.

 

[SCBO1]

I see this alot, but not allowed unless it's a Simpson approved hanger screw.

This is a packaging issue, if Simpson would sell hanger nails or their hanger screws with each hanger it would reduce this problem not to mention they would sell more product. The problem I see it is when you tell the contractor to remove the drywall screws, what should they replace it with, the nails would not get a good bite.

pc1

 

[GHRoberts]

Read footnote 2 in the NDS under wood screws... ASTM A 653, grade 33 steel and then lists bending yield strengths required. This is the old soft wood screw that the head stripped out before you got it driven. They are ductile and will bend like a nail rather than snapping like a drywall OR deck screw, that wasn't a recommendation, don't use those unless you see the designation listed on the box, which it isn't. A field demonstration might be to drive a nail and a hardened screw halfway into a dense piece of wood and then whack it sideways hard. The screw will likely fail, the nail will bend but hold. This is the difference between a ductile failure that screams in warning and a brittle failure that gives none. Since Simpson hangers are a proprietary engineered product I do believe they can list approved screws that have been tested to give tabulated results. I had a helper that thought screwing toeboards to the roof was a great idea, till he went rattling down by the dormer, screw sheared. I've had decking with juvenile wood shrink lengthwise and shear coated deck screws off.

Same footnote (different values) for hardened nails. Same footnote (different values) for standard nails. Not surprising.

"field demonstrations" are not useful in determining the suitability of either nails or screws. Anecdotal evidence is also not that helpful.

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Showing the suitability of screws is accomplished by doing the engineering. The AHJ should only be asking for the engineering not acting like he knows the answer already.

I should add that one can obtain the properties of whatever screws they wish to use and produce their loading tables from the formulas.