Jamb Saw

[C.J.]

Depends on if they are a fire/smoke break, or just a steel door jamb for the sake of being a steel door jamb. My favorite is when dummies come running out of the wood work to tell you not to undercut a steel door jamb because it is against "code" and neglect to realize they are hollow, have wooden hollow doors hung on them, are interior to a unit and are already off the ground and lack fire caulking.

There are a very great amount of things that people just do not question, yet they heard one thing one time and that was their gospel

I’m one of those dummies. If I lived in that world anymore I would prolly know what’s what by now but I’ve been doing strictly residential for the past 10 years and there aren’t many steel door jambs in my world. Even if I ran across one now I wouldn’t undercut it because I wouldn’t be willing to trash a decent blade for the sake of a door jamb.

 

[Mark Brown]

They make blades for the jambs. Just a cut off wheel. I typically only break it out for tile and wood.

My ultimate favorite is when a GC will tell me I cannot undercut a door when installing tile on a commercial site. "Those are Fire Rated" he will come along and say... at which point I love to point out the lack of a threshold, no door sweep, the fact that the damn frame is already off the floor by 1/4 inch. They don't think these things through. There are door systems that are designed to be completely draft proof for smoke ingress but more often than not, it is simply the door that is rated as a fire break. This is why solid core wood and fire rated steel doors have those rating tags. No tags, no rating.

 

[Mark Brown]

I’m one of those dummies. If I lived in that world anymore I would prolly know what’s what by now but I’ve been doing strictly residential for the past 10 years and there aren’t many steel door jambs in my world. Even if I ran across one now I wouldn’t undercut it because I wouldn’t be willing to trash a decent blade for the sake of a door jamb.

You never make it into the crappy 70's apartments where everything was a bloody steel door frame for reasons i will never ever ever understand?

 

[Mark Brown]

And then there is the actual code on the matter for anyone who cares...

NFPA 80, Fire Doors and Other Opening Protectives, contains information on maximum gap allowances for different types of fire doors. In general, those allowed gaps are as follows:

» Clearance for under the bottom of a door: 3/4”

» Clearance between door and frame: 1/8”*

» Clearance for meeting edges for a pair of doors: 1/8”*

For more detailed gap information, refer to NFPA 80, Section 6.3.1.7 and Section 4.8.4.1.

https://www.nfpa.org/assets/files/AboutTheCodes/80/80_A2018_FDW_AAA_FD_CIStatements.pdf

 

[C.J.]

You never make it into the crappy 70's apartments where everything was a bloody steel door frame for reasons i will never ever ever understand?

The projects? Nope. A doctors office or something like that is where I would run into steel jambs and not many of them were floating floors. Carpet, glue down LVP or sheet goods were all cut tight.

Done plenty of multi family. Front door is fire rated steel jamb so leave it alone. Everything else was wood.

Prolly more BS but I’ve heard another reason to not undercut is because of the weight of the (commercial) doors. Good to know the actual code even if I don’t live in that world.

 

[Mark Brown]

The frames are not dependent on contact with the floor. I can demonstrate this in great detail if you wish in the **** project I am working on now where a quarter of their frames do not even contact the floor due to the floors being so bloody out of plane that it would be impossible without cutting down the damn door or frame.

There is just so much hearsay in trade work I have found and what I have noticed a lot less of is people doing a bit of digging to find out what really is. I have heard so very many things are "against code" and this and that and I just scratch my head, the information is all readily available on the internet, usually not just hanging out on the top of google search results but buried in some PDF from the related governing body.

I, like yourself, use to run underlayment perpendicular to sub-floor for the same reason you did. It was what I heard and it made sense in my brain to think cross stacking meant strength. Then one day I got into a heated argument with a man who was shooting 5/8 sheathing staples into my underlayment because GC was responsible for installing it and "I have always done it this way, I have done hundred of houses and never had a problem" so I went home and printed the instructions from Tolko for installing ULay and there in the bold writing was to run then parallel. For the record, it did not mention anything about using 5/8 sheathing staples and the next day when I delivered said instructions to subfloor man and the GC they happened to own a new narrow crown underlayment stapler. From there it was on to the APA installation instructions and boy oh boy did a learn a lot. I find as I get a little older, my quest for knowledge is diminished a little from my early 20's but my curiosity remains.

 

[C.J.]

I find as I get a little older, my quest for knowledge is diminished a little from my early 20's but my curiosity remains.

I would agree with that. Years ago I never knew what the day was going to throw at me so you had to know everything. These days I’m more optimized than maximized. I don’t do everything anymore and if I need to know something specific it can be googled in a few minutes

 

[highup]

I would agree with that. Years ago I never knew what the day was going to throw at me so you had to know everything. These days I’m more optimized than maximized. I don’t do everything anymore and if I need to know something specific it can be googled in a few minutes

......or you can just come here.