Interesting study on strength of drywall screws

[Jack Feldmann]

I frequent this site for woodworking stuff. A while ago he did a test on the strength of drywall screws. Some of you might find it interesting.
https://woodgears.ca/joint_strength/drywall_screws.html

[Claude Lawrenson]

Great site - thanks! Even found some of the other references terrific.

[Jack Feldmann]

Each Friday he posts a new video. Great stuff if you like making sawdust.

[Gunnar Alquist]

Of course, one of the things that we see is improper use of screws substituted for nails and he does not address that issue.

[Jerry Peck]

Of course, one of the things that we see is improper use of screws substituted for nails and he does not address that issue.

And drywall screws used where wood screws or sheet metal screws (which have similar bending and strength properties) should be used.

The brittleness of drywall screws is a critical factor.

Simpson makes screws approved for many straps and anchoring uses - and those screws bend like nails.

[Jack Feldmann]

I think it should be taken in the context he meant. He was responding to comments about him using drywall screws in his projects.

[Jerry Peck]

I think it should be taken in the context he meant. He was responding to comments about him using drywall screws in his projects.

I suspect most understood that, I also suspect that some (and many contractors/installers apparently have) taken drywall screws as being suitable substitutes for other screws ... and use his tests as support for using drywall screws when and where other types of screws should be used.

[Jack Feldmann]

I suspect most understood that, I also suspect that some (and many contractors/installers apparently have) taken drywall screws as being suitable substitutes for other screws ... and use his tests as support for using drywall screws when and where other types of screws should be used.

I'm probably reading your comments wrong, or maybe I'm missing something in his video, but I don't think he was saying that drywall screws are better than other screws for all applications. He did comment on the heads popping off, and that they were brittle, so obviously, they are not appropriate for all uses.

[Jerry Peck]

I'm probably reading your comments wrong, or maybe I'm missing something in his video, but I don't think he was saying that drywall screws are better than other screws for all applications. He did comment on the heads popping off, and that they were brittle, so obviously, they are not appropriate for all uses.

Jack,

I understand what he said and why ... but some ... some may take his 'tests' as confirmation that drywall screws are suitable for things they are not suitable for.

[Jack Feldmann]

Honestly, Jerry, you are probably the only person that can take a woodworking information video and try to turn it around to make the guy a bad guy for misleading, or misguiding "some" people.

[Jerry Peck]

Honestly, Jerry, you are probably the only person that can take a woodworking information video and try to turn it around to make the guy a bad guy for misleading, or misguiding "some" people.

Honestly, Jack, you are probably the only one taking my posts as accusing him as being a bad guy and putting out misleading information ... I suspect that everyone else is taking my posts as pointing out just what my posts have been saying - that some people could refer to his 'tests' as justification for their using the wrong screws for the wrong purposes.

Somehow, and for some reason, you are hitching the horse to the back of the cart and trying to push the cart instead of pull the cart (getting everything bassackward).

[Paul Douglas]

I find the testing apparatus interesting. My only comments would be that usually for wood connections the allowable capacity is typically based on a safety factor of 4 to the ultimate load/failure. The current and recent wood design codes recommend pre-drilled holes for screw type fasteners to prevent splitting and the diameter is depends on the root diameter of the threads and the specific gravity/density of the wood.

I would imagine that most contractors do not spend the time to pre-drill holes.

[Jerry Peck]

I find the testing apparatus interesting. My only comments would be that usually for wood connections the allowable capacity is typically based on a safety factor of 4 to the ultimate load/failure. The current and recent wood design codes recommend pre-drilled holes for screw type fasteners to prevent splitting and the diameter is depends on the root diameter of the threads and the specific gravity/density of the wood.

I would imagine that most contractors do not spend the time to pre-drill holes.

I'm not following on that splitting issues and pre-drilling holes for screws - no one does, or even recommends, pre-drilling holes for nails, which have the same or similar wood splitting issues.

I know that pre-drilling is recommended for larger size screws (such as lag bolts) due to their larger size (5/16" or 3/8" and larger as I recall).

Smaller screw sizes have the same basic splitting issues as nails.

And yes to the safety factor rather than ultimate failure being used for a strength/load capacity.

Paul, being an engineer, do you know what the size was for the pre-drilling recommendation?

[Paul Douglas]

I'm not following on that splitting issues and pre-drilling holes for screws - no one does, or even recommends, pre-drilling holes for nails, which have the same or similar wood splitting issues.

I know that pre-drilling is recommended for larger size screws (such as lag bolts) due to their larger size (5/16" or 3/8" and larger as I recall).

Smaller screw sizes have the same basic splitting issues as nails.

And yes to the safety factor rather than ultimate failure being used for a strength/load capacity.

Paul, being an engineer, do you know what the size was for the pre-drilling recommendation?

Based on the 2005 edition of the ANSI/AF&PA NDS-2005 (National Design Specification for Wood Construction ASD/LRFD) which is referenced by the 2006 IBC/IRC Section 11.1.4 Wood Screws it depends on if the screw is loaded in withdrawal or shear also. It would take me a long time to type that section and I think I would get in trouble with copyright laws if I copied and attached it. But let's say we have spruce-pine-fir (SPF) with G = .42 loaded in withdrawal pre-drilling is not required for a lead hole. But G b/w .5 and .6 shall be 70% the root diameter, and G>.6 is 90% the root diameter. For screws loaded laterally with G<=.6 the lead hole for shank is 7/8 x shank diameter and lead hole for threaded portion is 7/8 x root diameter. With G > .6 then lead hole in shank same dia. as shank and lead hole for threaded portion is same as root dia.

Lag screws have different requirements. The 02, 98, and 95 versions of NDS I believe are the same. I don't have the 2010 version of NDS yet.

I would typically specify per the NDS code to cover my butt knowing that it may not be done.

[Mark Reinmiller]

I briefly looked at this and gave up. First, most of the screwsupply shown would more accurately be called general purpose screws. Most are also typically much stronger than drywall screws. The tests I looked at had nothing to do with shear strength, which is very important criteria. Also, since these types of screws are not structurallying rated the test results could vary a lot. I'may not sure why anyone would consider this information to be credible or meaningful.

[Raymond Wand]

Don't even get us Canadians started on Philips head versus Roberston headed screws.

[Garry Sorrells]

Don't even get us Canadians started on Philips head versus Roberston headed screws.

Why bother, they are being replaced with star drives.:p But then you guys need something to do to pass the long cold nights up in the north woods.

[Jack Feldmann]

When working with hardwoods, if you don't pre drill for screws, the wood will likely split. While it doesn't apply to general construction, when building cabinets, jigs and fixtures, or other project using hardwoods, its common practice to pre drill. There are special bits made to pre drill and countersink for each common screw size. I don't know anyone that uses nails when working with hardwood (building cabinets, etc.)

[Paul Douglas]

When working with hardwoods, if you don't pre drill for screws, the wood will likely split. While it doesn't apply to general construction, when building cabinets, jigs and fixtures, or other project using hardwoods, its common practice to pre drill. There are special bits made to pre drill and countersink for each common screw size. I don't know anyone that uses nails when working with hardwood (building cabinets, etc.)

It applies for any general construction considered as any type of structural element including walls. But as Jerry indicated it typically never gets done. Not a problem unless splitting. I believe allowable lateral load capacity would be reduced and depends on the direction of load relative to angle of grain. I hope that makes sense. Like splitting a log with load parallel to grain is easier than going perpendicular to the bark/grain.

[ROBERT YOUNG]

It applies for any general construction considered as any type of structural element including walls. But as Jerry indicated it typically never gets done. Not a problem unless splitting. I believe allowable lateral load capacity would be reduced and depends on the direction of load relative to angle of grain. I hope that makes sense. Like splitting a log with load parallel to grain is easier than going perpendicular to the bark/grain.

I concur.
This article mentioned sheds did it not? Sheds can take some abuse just getting erect by a novice.
During my rough carpentry days drywall screw dependability was compromised significantly when ever I demolished structures.
When I erected decks I sure powder coated deck screws and they never failed.

Great read.
Thanks.