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code question

Posted by qwertyui (My Page) on
Wed, Nov 4, 09 at 0:04

Is there anything in most building codes about using heat treated screws (AKA sheetrock screws) for structural applications?? I know it's a bad idea, I was just wondering if it's illegal?


Follow-Up Postings:

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RE: code question

The code requires nails.

There is no listing for drywall screws in anything but drywall applications.


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RE: code question

Illegal or not, which I believe it is against code for shear reasons concerning structural, you never want to use them in a stuctural situation. Drive one in a peice of scrap wood about halfway, take a hammer and bonk it from the side. It will snap in half with very little effort!


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RE: code question

Type W drywall screws are allowed in 1 & 2 family dwelling building codes for the installation of interior gypsum board and exterior gypsum sheathing as per reference standards GA253 and ASTM C1002.


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RE: code question

What brickeye said.

Drywall screws can be used in absolutely no structural application.

Period.

Good job, brickeye...


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RE: code question

Brickeye's statement is entirely correct but since he is a professional I'm sure he didn't mean to imply that drywall had 'absolutely' no structural application.

Drywall screws are listed in IRC Table R602.3(1) 'FASTENER SCHEDULE FOR STRUCTURAL MEMBERS' for installation of exterior gypsum sheathing on wood or metal framing.

Such wall systems meet the IRC lateral structural bracing requirements for exterior wall panels per section R602.10.3(5) with drywall screws from Table R602.3(1) at a maximum spacing of 7 inches on center. Interior bracing walls are covered in section R702.

Drywall screws may not be very effective or allowed for wood connections but they are by far the most effective fastener for transferring shear forces in gypsum wall panels as can be seen in GA 229 'SHEAR VALUES FOR SCREW APPLICATION OF GYPSUM BOARD ON WALLS' where they are said to be more effective than nails.

I designed a multi-story elderly housing project laterally braced by interior drywall panels on metal studs which were designed by a structural engineer. I'd say that was a structural application.

Here is a link that might be useful: shear strength of drywall screws in drywall


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RE: code question

Drywall is NOT a structural entity.

It does not hold up anything but itself, and possibly insulation.

The "FASTENER SCHEDULE FOR STRUCTURAL MEMBERS" provides allowable fastener schedules based on what the drywall is being attached to (the "structural member").

It does not imply the drywall and screws are structural elements.

Even shear panels of plywood cannot be attached with drywall screws.

One of the things that keeps wooden buildings standing is the structural over design used since the material have rather large variation in strength. If you go to higher grades of lumber the allowable loads increase since the material is more uniform.

Steel nails are very malleable.
If overloaded they will bend without breaking.
Not so with hardened screws.

The load bearing rating of nails depends on the species and grade of lumber they are driven into, as well as depth and nail size.

Generous margins are still required since a nail could be adjacent to the largest defect allowed in a grade of wood.

Determining nailing schedules for 'designed' connections takes a decent amount of time.

Loads must be accurately computed, then summed for the member, then enough fasteners of the correct size placed to provide a secure long term joint in the specified materials.

After you run through it a couple times you start to keep a 'cheat sheet' that summarizes things so you do not have to drag out all the standards over and over.


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RE: code question

Are you suggesting that the shear values shown in GA-229 are fictitious?


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also

The tested shear values of structural shear walls made with gypsum panels are accepted in all model building codes but the values are usually reduced by 50% for seismic zones 3 & 4 which is much of the western third of the US.

The link below shows some general capacities for different shear wall sheathing materials. The values for gypsum board shear walls are increased when drywall screws are used.

Here is a link that might be useful: different kinds of structural shear wall materials


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RE: code question

"Are you suggesting that the shear values shown in GA-229 are fictitious?"

Yes, as a matter of fact they are.

The code is a minimum, and as a PE I do not and will not rely on gypsum for ANY shear rating.

When you can pull the stuff off with your bare hands and very little effort, it is not worth trying to claim it has any significant shear strength.


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RE: code question

The question was:
"Is there anything in most building codes about using ... sheetrock screws... for structural applications?"

I gave him what I thought was an accurate answer.

What you wish to use or not use professionally doesn't make my answer inaccurate.

Being a PE doesn't give you the right to be disrespectful of others. I had the same engineering education specializing in structures and went on to get a Masters in Architecture. I hope that permits me to answer questions here.


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RE: code question

Never said you could not answer questions, but picking a single (and poor) use of drywall screws to anchor drywall resulting in limited structural use is at best very misleading.

You will also note that in areas that actually require seismic stiffening the ratings for drywall are cut in half, reducing them to a uselessly low value.

Using drywall screws to fasten structural lumber members together is not allowed.


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RE: code question

No one said drywall screws were allowed by code for lumber connections.

To say that exterior gypsum sheathing is not allowed by code as lateral structural bracing for a single family home is simply incorrect regardless of your opinion of it.


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RE: code question

"I designed a multi-story elderly housing project laterally braced by interior drywall panels on metal studs which were designed by a structural engineer. I'd say that was a structural application."

Not to dispute you or any scholarly engineer, but that sounds like pushing the boundaries of practicality just a wee bit.


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RE: code question

You've probably been in metal stud bearing wall buildings without realizing it; they don't look any different than wood stud bearing wall buildings but they meet the requirements for non-combustibility normally required for multi-family dwellings over a certain size. It's not a matter of practicality but of life-safety and cost.


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RE: code question

Deck screws, drywall screws and Grabber screws are all typically used (and for my $ quite welcome) in non-structural framing applications. I'm thinking bulkhead/soffit construction, where small-bore members (2x2, 2x3) are being used, and where the entire thing gets wrapped with plywood anyway. The screws pull the framing members together tightly, and will not creep apart as the wood dries out and warps. But Lord, no, never in load bearing or structural applications. For that god created Timberlock screws.
Casey


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RE: code question

I guess I could have been a little more specific. How about using for hanging kitchen cabinets? Manufacturer specs a size and quantity of screws but doesn't mention type.
I've already added non-heat treated screws, so the question is academic at this point.


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RE: code question

Definetely DO NOT use drywall screws for cabinet installs. It is a structural application especially concerning the uppers. Use a hardened screw. Something like these:

Here is a link that might be useful: Mcfeeleys


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RE: code question

Drywall screws are not actually heat treated which would affect the properties of an entire piece of metal; they are case hardened, which only hardens the surface of the steel to a minimum of .002 inch deep which is about 3% of the cross-sectional area of a typical #6 drywall screw. This toughens the surface of the screw but should not affect the ductility of the interior.

Of course, the ductility of the screw is determined by the grade of steel used which is usually 1018. Building codes and industry standards require drywall screws to be able to be bent to an angle of 15 degrees without showing signs of fracture. In practice I have found that they will go beyond 45 degrees but there is no way to predict at what angle they will lose their pull-out strength or fail.

I am not sure why drywall screws are not as malleable as nails; it could be the cold heading process (suspected of causing internal ductile failures) but since the manufacturers design to the ASTM standard, you have to expect the screws to fail beyond an angle of 15 degrees. I wonder how far a similarly sized standard wood screw would bend. Perhaps they are also subject to the problems with the cold heading process.

However, the common claim that drywall screws have a low shear strength is not based on factual test information but probably on a misunderstanding of the difference between shear and bending strengths. Drywall screws haven’t been formally tested for shear in wood connections because they are not designed or manufactured for that purpose but because of their thin shank no one should expect them to be particularly effective in wood even though they have been tested to high shear values in metal framing.

What you can be sure of is that if a connection deforms enough to allow a drywall screw to bend much beyond 15 degrees, it is likely to break. Whether that is better or worse than a similarly sized nail or a standard wood screw would be pure speculation so if you want a safe connection you must use a screw designed and tested for wood connections. I like the Simpson Strong-Drive Screws (SDS) if only for the good strength information they provide.


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RE: code question

In field experience, I dont recall seeing a drywall screw bent. They snap I would say well before even a 15 degree "bend". They're an awesome fastener for wallboard and even in "handy andy" projects, just not for anything structural outside of the metal farming/wallboard you mentioned when used. I consider, (even though it's not recognized by engineers, building pros, codes, etc), interior walls being a "brace" when sheetrocked. It has some value of strengthening an interiors structure at least laterally and only somewhat, but still added value, imo. I realize this excludes shear, lift calcs, and loads, but still is a brace.


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RE: code question

macv, Where did you get the idea that sheetrock screws are case hadened? They certainly don't look like like it when they break. Case hardening is an expensive process compared to just making screws out of 1030 or 1040 steel. and doing a quick quench and temper.

I was using "sheetrock screws" as a generic term for cheap hardened screws with a skinny shank. I doubt anybody actualy hangs sheetrock with #8 X 3 1/2" screws. Standard steel screws will bend well beyond 90 deg without breaking. almost as good as nails.
Drywall screws vary a lot on how far they will bend I tried several different boxes and different brands that I had accumulated. Most cracked at less than 45 deg. None made it to 90 deg.


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RE: code question

The 15 degree bend, case hardening and steel grade are requirements of ASTM C1002 which is the standard stipulated by GA 253 which is the standard stipulated in model building codes (IBC, IRC, etc.) for the installation of exterior gypsum sheathing and interior gypsum wall board.

I suppose there is a manufacturer that makes drywall screws that would not meet the minimum code standards for a single family house but I don't know why a reputable building supply store would knowingly sell them.

from ASTM C1002:

5.1 Steel Wire, for manufacturing screws, Specification A 548, Grades 1013 to 1022.

6.1.1 The surface of Type S and Type W screws shall be case hardened to a depth of not less than 0.002 in. (0.05 mm) with case hardness not less than 45 HRC.

12.6.5 Ductility Test − Hold one end of a screw specimen in a vice. Hold the other end with the locking pliers and bend the screw to an angle of 15 [degrees]. Observe for signs of fracture in the screw shank.


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RE: code question

Common drywall screws are normally sized to be used in UL-tested fire-rated wall assemblies using from 1 to 4 layers of 5/8" Type X rated drywall. Two layers requires a 2 3/8" screw and 4 layers requires a 3 5/8" screw.

Such long drywall screws are rarely needed today because of the introduction of 1/2" Type C rated drywall, Shaft Walls, and sprinklers, but they are still manufactured.


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RE: code question

I just checked my "warehouse". out of 8 boxes of heat treated screws, one is actualy labeled "sheet rock screw".
none list any spec or code. No telling what Home Depot is selling!


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RE: code question

It costs very little to manufacturer a drywall screw and the requirements of ASTM C1002 are low. I cannot imagine why a manufacturer would make substandard ones and I'm sure many far exceed the standard. Why would they eliminate themselves from competing in the larger commercial market where a contractor has to submit evidence of compliance for every product used in the project? The major manufacturers (Milwaukee, Grip-Rite, etc) comply and they are likely to supply Home Depot.


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