ECN Forum Forums General Topics of the Trade General Discussion Area fishing in plaster ceiling

As an engineer, I strongly advise against notching joists. The highest stresses in a beam are carried in the outermost fibers of the beam. When you notch a beam (joist), you are essentially reducing the depth of the entire beam by the depth of the notch. Say, converting a 2x10 into a 2x9.

The stiffness of a beam varies as the cube of the depth of the beam. So, in the case of a one inch notch in a 2x10, you're causing a 28% degradation in the stiffness of the joists. That's major damage to the quality of the floor above, and possibly a dangerous reduction in the strength of the floor.

It is also a violation of building code to notch the center 1/3rd of a joist or rafter.

Also, building code requires holes to be a minimum of 2 inches from the edge of the joist or rafter. Like the engineer said, the stresses in the wood is in the outermost fibers.

Notching the beams 1"?

That's a big area. Nm is what, 3/4" long, 1/4" thick.If you take out the drywall that is prob 1/2" thick, you only at best have to trim the bottom of the beam 1/4" deep to lay the NM in, then if you screw a steel nail plate on, how is this affecting the beam strentgh itself.

I've seen guys notch too much, which is silly, and Have seen guys drill holes in them "particle board" beams, which is a huge problem there.

I think Texas Ranger has the right approach. Why go thru all that risk and patching when you can just go the long way around? The intuitive thinking is to go from 1st base directly to 2nd base but you have maybe eight joists in the way. So you go from 1st to home to 3rd and then to 2nd with no joists, structural issues and patching. Romex is not that expensive.
Again, good point, Mr. Ranger.
~Peter
Another point. Does anyone make a borescope about 1/4" in diameter? It soes not need to be flexible but could operate like a little periscope.

Why go thru all that risk and patching when you can just go the long way around?

Huh? You have to go across a ceiling against the joists maybe to install some cans. How are you going to go around?

As an engineer, I strongly advise against notching joists.

Agreed. Notching joists is a result of trying to be neat at the expense of weakening the structure. Don't want to weaken the structure? Might as well (neatly) Sawzall out a 4" wide strip of sheetrock or plaster and drill the joists in the center as you would if the ceiling were open.

-Hal

I think hbiss got it. Just open one long 4" wide strip and drill the joist properly. The drywaller will have an easier time patching one long hole than a bunch a tiny ones. Plus you will be out of there that much faster. I like to use a vacuum and a rotozip in plaster. Don't forget to draw some straight lines as guides or you haven't done you or the drywaller any favors.

Remember, sheetrock is really, really, really cheap--like ~$6 sheet. There's an instinctive desire to "minimize the damage" by keeping the holes as small as possible. But the reality is more like what hbiss and kinetic said--it's easier to patch one hole that's 4" wide and 12 feet long. Just cut one or two strips of rock, slap it up there, and you're ready to tape and mud it. You've maybe got 75¢ worth of rock in the patch--there's not much point in spending another three hours carefully cutting a bunch of tiny holes so that they only need 25¢ worth of rock to patch all the tiny holes.


[This message has been edited by SolarPowered (edited 02-08-2005).]

We all know that the sheet rock ceiling is easy to cut and patch but what about the lathe and plaster cielings? I use a 4" hole saw and patch with a 4" hole saw cut of sheetrock. I find this burns through the hole saws very quickly though. Curious if there are any better ways to cut through lathe and plaster?

I use a 4" makita grinder with a thin diamond blade to cut thru lath and plaster. It makes a lot of dust but you can cut thru simular to a sawzall with out a lot of the vibration of a sawzall. Having a good shop vacuum hose next to the blade cuts way down on the mess.
Fixing lath and plaster is more expensive than drywall but over all is usually cheaper than spending hours trying to fit diversabits or a lot of extensions thru a small hole.