Lag screws for residential projects

[DoubleStud]

Questions to those who do a lot of residential wood projects. With structural wood screws getting more and more popular, do you still specify lag screws? I have so many standard details that I copy and paste for each project where I specify lag screws. One example I have is when I have a steel beam bearing on a stud pack. My standard detail shows a 1/2" dia X 4" lag screw each side of the web. I am wondering if I should start replacing them with structural wood screws like Timberlok or Simpson Strong Tie? What do you guys do?

 

[dik]

I spec wood screws more and more... but often the material I get to review uses lag screws, and I note the others as an alternative.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

I've never spec'd lag screws unless there is no viable alternative. I don't trust anyone to install them properly...

 

[Aesur]

I have been replacing lag screws with wood screws, most commonly Simpson SDS or Simpson SDWS and only using lag screws when needed. It is my understanding that the wood screws are cheaper and most often adequate for use, and ultimately saves me time specifying as the information is more easily found/calc'd.

 

[XR250]

My standard detail shows a 1/2" dia X 4" lag screw each side of the web

Seems like a pretty big fastener to put into the end grain of a 2x. Maybe it IS the time to revise your details?

 

[jayrod12]

I'm in the same boat as phamENG, the predrilling requirements are never followed, or they end up overtorqued so they just strip all the material out of the hole. MTC, GRK, Timberlok, Simpson etc, all have their form of self drilling wood screws that have impressive capacities and no pre-drilling required except in rare circumstances.

 

[manstrom]

I stopped using them a long time ago.

 

[DoubleStud]

XR250, indeed. Not too worried about it since it is a big stud pack and only taking vertical load. Thanks guys! I will slowly update my details. Maybe I will call out a manufacturer and say or approved equal?

 

[Craig_H]

Maybe I will call out a manufacturer and say or approved equal?

Proceed cautiously; to the best of my knowledge, all the "structural screw" manufacturers have proprietary quirks that make their capacities differ. It is my understanding that the screw thread cross-section and slope differ slightly between manufacturers and this is where they try to compete on ease of driving and lack of pre-drilling requirements. This might not be a factor for your chosen example of a steel beam bearing on a stud pack, but especially for withdrawl, make sure you look carefully at each manufacturer's information and it's validity.

In my area, the GRK products are widely available and are the norm. The way that they determine their capacities is quirky and in a bit of a grey area. The fastener diameter is slightly larger than permitted by my code (CSA O86) for wood screws, and yet they determine their capacities per the provisions of that part of the code rather than via the lag screw portion of the code. I understand the rationale and have personally accepted it, but you should aquaint yourself with the peculariarities of the manufacturer and make sure you are comfortable with it.

 

[Eng16080]

I can't recall the last time I used lag screws. I typically use wood screws, nails, and thru bolts for wood connections.

There are a lot of great proprietary wood screws available (Simpson, GRK, etc.). Having done various carpentry projects, I'm a big fan of GRK screws from a strictly construction perspective. They drive into the wood so easily compared to the generic wood screws you might get at a hardware store.

Along the lines of what Craig_H mentions above, having looked at some of the technical literature for these proprietary screws, the reported load values can be misleading. Make sure you read all of the footnotes and disclaimers before using those values. These companies are trying to sell screws, and they have an incentive to show higher values than a competitor. In designing connections with wood screws, I typically only use the values provided in the NDS code, even if I specify a proprietary product. Even if one proprietary screw is stronger than another (meaning that it has a higher steel strength), the limiting factor is likely to be a failure of the wood anyway.

 

[Brad805]

GRK has an ESR report now. GRK RSS ESR

At one time we were getting asked about lags, but now I suspect if we showed them our trades would ask about substitutes. They have figured out the time savings v cost. We tend to spec GRK like Craig, but discovered recently that MiTek has gotten into the market. Simpson are not widely available, and many of our wood trades are not great planners.

 

[dik]

on one of the Mike Holmes episodes, his guy was installing them with a hammer. also, overtorquing them and stripping the threads is an issue.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[XR250]

If you keep them to 3/8" Ø and under, I don't think they require pre-drilling.