I started a home project assuming that there are wooden joists/studs (what’s the difference?) running one way or another across the ceiling under the plaster. The ceiling is 8 foot 11 inches high, so I doubt there’s a big gap between the ceiling and the next floor. Anyway, all I seem to find with the stud dectector seems to be metal (that was the A/C register … :smack: ) or something hard that might be metal or concrete. Is it possible I have no wooden studs in the ceiling? I live in a four story condo building.
Generally the term ‘joist’ refers to the member shich support floor areas.
In a four story job one man’s floor is another man’s ceiling.
Studs form a wall between the plates and provide nailing surfaces for lath,wall board etc as well as providing lateral stability to the frame.
If it’s a four story building the ceiling/floor might be a pre-tressed concrete slab held up by load-bearing walls.
If you have a ceiling fixture you might be able to lower the esscutchion and see just what the heck you’ve got up there.
Ltsa luck from
OL’EZ
Assuming that the ceiling is 1 hour fire-rated ordinary construction, you should be able to determine location of floor joists. If local codes required a 2 hour rating, your sensor may not do the job. Beyond that, if the ceiling construction is plaster over expanded metal, the sensor isn’t likely to detect joists at all.
Well, it dectects something. And there’s space inbetween that when I drill through the plaster it is just empty. I just can’t tell what it is. The floor plans have some 1 hour and some 2 hour, but I couldn’t figure out from them where the joists in my ceiling are. I guess I could just cut open a 1/2 inch square and look. What would I repair that with?
How old is the house? If it’s more than a decade old then it almost certainly has wooden floor joists.
To find the joists, drill a small hole in the ceiling roughly where you want to open the ceiling. Insert a piece of clotheshanger bent in an “L”, and twist it around to see where it hits a joist (the part inside the ceiling should be at least a foot long.) You will probably hit joists at four points and should be able to determine where two joists are (this will also roughly give you the joist spacing across the ceiling) and which direction they’re running.
Assuming that we’re not dealing with ‘heavy timber’ construction, the joists should fall on 16 or 24 inch centers. Before cutting a hole, borrow a stethoscope and knock on the ceiling. The sound change under a solid member will be audible.
The post by cornflakes brought this to mind- joists run perpendicular to the roof ridge, 9 times out of 10.
It’s a square flat roofed building, four stories. About 20 units of condos. There are ceiling registers that run north south across the room, so I thought the joists would run parell to them, but don’t seem to. Is there other stuff up there that might be dangerous to drillin to? 
Thanks for the advice.
Questions.
“joists/studs (what’s the difference?)”
JOISTS, floor (or celing in multi floor)
STUDS, vertical wall members
PLATES, horizontal wall members (sole plate, bottom, top plate, top)
BEAMS, horizontal structural support members,
POSTS, vertical structural members
RAFTERS Inclined roof support members
RIDGE PLATE, the top part where the rapters are nailed
HIP PLATE, the bottom part where the rafters are nailed
TRUSS, pre fabricated roof support members
RISERS, The front part of a stair
STRINGER, The side part of a stair
LATHE, little strips of wood nailed to the studs to support plaster (usually acompanied by)
MESH, looks kinda like chicken wire, It helps keep the plaster from cracking.
(last two pretty much made obselete by drywall.) but you may encounter them.
HEADER, Additional load bearing support over a door or window to keep them from binding.
Bear in mind, I am pulling these out of my ass and I haven’t been a framer for several years.
“Is it possible I have no wooden studs in the ceiling?”]
I’d bet on it. Ive never worked on a wood framed structure over 3 stories in my life. Not to say they don’t exist but they would be rare.
Even a masonry walled unit, with wood internals is extremly rare over 2 stories.
My guess would be masonry walls with pre fab concrete beams @ 24 on center w/ 2x4 plates nailed w/ 3/4 ply sheathing as sub floor. but thats just a WAG Ive been wrong many times before.
You should also check your condo home owners documents–it is likely you don’t ‘own’ the space behind the finish surface of the wall or ceiling. These studs and joists, etc are typically considered ‘common elements’ and usually you are not allowed to mess with them.
On a older 4 story building I would assume you have a conventional concrete slab–Post Tension concrete slabs are a relatively recent invention. Another possibly floor is a preformed concrete “T” beam as mentioned by EvilGhandi. A much smaller likelihood would be joists–could be metal joist with a concrete topping, or less likely but possible it would be wood joists. Forming your ceiling could be one or two layers of drywall and/or plaster.
I am an Architect–but I am NOT giving you any advice over the internet here–you should hire either a Contractor or an Architect to give you some advice on what they can see. In addition my advice would be to contact your Home Owners Association before you attempt to do anything here. HOA tend to frown upon do-it-your-selfers.
Not only is it dangerous in some instances–ie. the Post Tension slab where the cable could be cut and basically slice through the slab as the tension is released, as someone has pointed out already, your ceiling is someone else floor.
Good luck! Probably not the advice you were seeking, but without knowing what your home project is this or seeing the actual conditions there is no wayanyone can give you better advice.
hakuna matata
Hakuna Matata,
Your advice was sound, no need for the legalese, you only told him what he/she should not do. But I feel the need to do the same.
Jeese what happened to our world?
Drhess, I am a licensed contractor but I am not your contractor, any advice I give is for information only. You should consult with the local authorities and your condo administrator before making any changes to possible structural members in your building.
The shortest span is typically used for framing members, e.g. in a 20 x 40 unit, the members will be parallel to the 20’ dimension. What else is up there? Electrical cables, domestic water supply, and waste lines. Damage one, and you’ll get to find out what is in the ceiling. :eek:
Just a thought, and it does not seem to have been covered yet, is that it is quite common practice to suspend the ceilings from the actual joists with “z” metal. this is done to reduce sound transmission through shared floor / ceiling situations. These will run perpendicular to the actual joists and will confuse a stud finder nicely.
That’s probably the case: the z metal. There is some sound insulation in their too. I’ll pull that plans out again tomorrow and post them or consult with a carpetner friend. As for the condo board, that’s me. 
Alternatively, I may just have to go for a wall mount. I’m trying to hang a heavy punching bag, 60lbs is all.
Re the Z metal: so the ceiling is a few feet from the joists? If so, that means I’m out of luck.
“the ceiling is a few feet from the joists”
Huh? No the ceiling, your ceiling is likely inches from whatever support holds up the next floor.
I fowarded the t-beam and plywood method, Hakuna let you in on the solid cast concrete idea. Both of us are experts in our fields yet you choose to ignore us.
It is very possible that some type of channel steel is running under a wood framed 4 story house and that your celing panels are attached to that. Don’t bet on it.
If it is, in fact, a sound reducing “z track” (unlikely) you cannot hang a punching bag off it. Unless you are interested in bringing down your whole ceiling.
You will need to tie into a structural support, be it wood, concrete or steel. This will involve drilling into and setting an anchor not only able to support the 60 lb bag but the force you put into it when you hit it. (I assume this isn’t just a decoration)
In my opinion you are in over your head, consult someone with building experience in your area. Preferably someone licencened to preform the work you want done. I doubt it will cost much.
Further,
tailake, I note your location to be Kona. I am a self employed contractor on Oahu, I’ve been in the building trade for over 20 years and I have yet to install a wall or ceiling on “z track” when it was not specificly requested. I’d like to know where you get this “commonly” idea from.
You do realize that that would add about $3000 to the cost of a new home and would probably run around 5-6 grand to retrofit an existing dwelling. Not to mention “z=track” is worthless unless you do all the other soundproofing including, caulking, insulation and air tighting the cavities between walls or floors.
Or maybe you were thinking of something else.
:dubious:
Calm down. I’m not ignoring nothing, buba. As I mentioned, I looked at the plans and there is clearly space there and the metal I am encountering is runing at right angles from the likely direction of the joists. I also stuck several nails in where the stud finder found something and only hit metal. Furthermore, I ran a coathanger up in one hole and could feel the soundproofing that was on the plans. I just wasn’t able to put it altogether. I agree I’m over my head and will have to look into another plan. Don’t get you knickers all in a bundle. Oh, and the distance between the ceiling the next floor up is at least a foot on the drawings.
Depends on where you are from. You might not see it much in your area. There’s a LOT of z metal sold. I’m just thinking of why the joists might be hard to find.
And yes the joists would be just 1 1/2 or so higher that the ceiling, and No I would NOT hang a punching bag from such a ceiling. If it did go bad it would be a really nasty repair job.
**drhess ** is trying to practice for a boxing match, and instead it looks like a p!ssing match has ensued. :rolleyes:
How about skipping the dad-blang ceiling entirely and buying / building a frame that sits on the floor to hold the bag? Unistrut oughta be more than strong enough for a 60# bag. It’ll definitely need some diagonal bracing so it doesn’t come down with a case of the wiggles and fall down.
Yes. I have a friend who is a carpenter. I’m going to have him look at my walls and I might just install a wall bracket. The stands that are sold are very space consuming. I 'm not sure, but maybe he can make something that would take up less space, or fold up for the closet. Anyway, end of discussion. Thanks for the tips, all.
Move along, move along…