Hi all,
I found a calculator http://www.awc.org/calculators/span/rev ... secalc.asp
which can show for a given span and a type of wood what size joists you need. Two important values are dead load and live load (psf). For a independent (room in a room) ceiling with double layer 5/8 drywall (and green glue of course!) what load values are recomended? Also, what defelction limit specification is recommended?
what ceiling loads to use to calculate joist requirements?
Originally posted at johnlsayers.com, topic 11194.
There's no "recommended value". Only the building code to comply with. The code is the minimum safety standard.
More information will be needed than "2 layers of drywall with green glue".
What species of lumber is available to you? What are the dimensions of your room? What will be your maximum joist span length? Are you using 16" OC or 24" OC?
I'm no expert so I can only share my experience. I believe you are dealing with a 'dead load' and not a 'live load', as I did on my project. My spans were about 10 ft. I built 24"OC, 3 layers of 5/8" drywall with GG between the layers. I used 2x6's, which were good in my particular build up to 15 feet. After I framed the room, I could hang on the joist, do pull-ups, etc. no problem. I wouldn't try that with a 2x4.
You can check out my little snippet regarding this subject on my build thread:
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=9166
These values are variables that are plugged into the calulator I provided the link for. Loading per square foot is a seperate (independent) variable which when combined with the other answers yeilds the joist size requirements. It seems to me that the loading per square foot of an independent ceiling assembly in a room-within-a-room configuration is something that could be stated without reference to the other questions you ask. Of course, adherence to code is the first requirement, but that doesn't mean there aren't typical values for this kind of construction, so as to get a rough idea from a calculator such as the one I referenced. I thought that there may even be "recommendations" to exceed code by a certain amount based on the non-standard facets of studio construction.What species of lumber is available to you? What are the dimensions of your room? What will be your maximum joist span length? Are you using 16" OC or 24" OC?
There are too many variables. All the data is in the reference section with the weights. Remember the dead weight includes the joists. If you want to exceed easily, use 1/480 for deflection. Beyond such generalities, significant calculations are involved, including three different types of limits, two of which are for catastrophic failures. AndreOf course, adherence to code is the first requirement, but that doesn't mean there aren't typical values for this kind of construction, so as to get a rough idea from a calculator such as the one I referenced. I thought that there may even be "recommendations" to exceed code by a certain amount based on the non-standard facets of studio construction.
What?! The loading per square foot is ENTIRELY dependent on the questions I asked!It seems to me that the loading per square foot of an independent ceiling assembly in a room-within-a-room configuration is something that could be stated without reference to the other questions you ask.What species of lumber is available to you? What are the dimensions of your room? What will be your maximum joist span length? Are you using 16" OC or 24" OC?
Why would a studio be different from any other structure?Of course, adherence to code is the first requirement, but that doesn't mean there aren't typical values for this kind of construction, so as to get a rough idea from a calculator such as the one I referenced. I thought that there may even be "recommendations" to exceed code by a certain amount based on the non-standard facets of studio construction.
I think you misunderstand me. I'm not asking about the load bearing capability of a particular ceiling - that would require knowing all the variables for that ceiling. What I am asking is what are the loads per square foot used to calculate joist requirments when the ceiling in question is a studio's room-in-a-room. I.e. the ceiling in question is right below another ceiling and so will never bear additional weight from above. Thank you AVare for pointing me to the reference section for weights. From there it seems the dead weight for drywall is 2.3125 psf for 5/8, and the joists themselves are no more than 2.7 psf even for 10" on 16" centers. For double drywall this adds to 7.325, so I would think using 10 psf for dead load would be sufficient. I don't know however where the live load value comes from in this situation since there will never be load added from above. I'm guessing that using another 10 psf here would sufficiently over-estimate the needs in order to figure joist requirements. Am I way off base here?What?! The loading per square foot is ENTIRELY dependent on the questions I asked!
I understand your point that from an enginieering point of view it doesn't matter what the room is used for, but from the point of view of rules-of-thumb, the specifics of studio construction would surely come into play. The reason I want rules of thumb like this is it allows me to get a handle on what is possible. If these calculation say I need 2x10 joists and I only have room for 2x6s, then I know that the design is not vaible and I need to explore alternatives.Why would a studio be different from any other structure?
OK = hang on a second here - just so everyone understands.
When calculating the load that will be inparted to structure it is critical that you take everything into account - including the wieght of the joists.......
BUT - when using a span table you do NOT do this - the table already takes that into account when it does the calculations.
To answer the posters question - if all you are going to do is hang drywall from the ceiling - then 10 psf dead load is fine - and yuo are correct that you don't need to apply any live load to a ceiling in this condition.
L/480 is a bit extreme for a ceiling without live load on it - that's the design criteria we use for ceramic tile or marble floors so they won't crack.
Typical floor design (for carpet - wood floors , floor tile/sheet vinyl) uses L/360 - which is designed to lay flat under dead load - which is more than fine for a ceiling that will never see a line load.
If you plan on using any ceiling clouds I would probably carry 15 psf DL - anything more than that is overkill.
Rod.
SD, those are all critical things you need to know if you are adding any load to an existing ceiling - but for the purpose of span tables - all of that is already taken into account. You input the span and the load you want to use - then begin plugging in joist sizes and available lumber species until you find the most economical means readily available to you. The total loads can then be calculated to see if you are exceeding a floor's capacity (if you are building on a wood deck for example) or to determine if you really need to take some concrete out to add haunches to carry your walls on. But you don't need that info to use the tables - the tables will guide you into a successful safe combination. Sincerely, RodThere's no "recommended value". Only the building code to comply with. The code is the minimum safety standard. More information will be needed than "2 layers of drywall with green glue". What species of lumber is available to you? What are the dimensions of your room? What will be your maximum joist span length? Are you using 16" OC or 24" OC?
Andre my friend, I think you misunderstand slightly the concept of deflection design. It certainly is not intended to be a case where you can exceed the loadings. All it does is calculate for a stiffer member - with a then shorter span because of the added restriction on deflection. You can then (of course) look at it in the other direction and see what the actual capacity is of that joist with a less restrictive deflection criteria - but it is not intended for the purposes of feeling safe if you over load to any extent. The best method is to determine exactly what you want to load - and then add something for the unknown in the possible future - then use a deflection design that accomodates your real real needs. For as simple ceiling that could never possibly see a live load - L/360 or even L/240 would be more than adequate. Remember - the only thing that the deflectuion is calculating is what the laydown will be under load. As example, in the Internation Building Code used here in the states - the required floor design for wood frame construction is L/360 for live load - and L/240 for L+D loads. For roof members supporting a drywall ceiling it's L/240 for LL - L/240 for snow/wind loads - L/180 for combined Live/Dead Loads. A factor as small as L/180 would be code compliant for a ceiling load in construction whre there could not be storage above the ceiling. The only time you get into issues with a potential for catostrophic failure is when you begin doing calculations where you start tweaking things closer to the unity of the member - but span tables use a very heavy margin of safety - probably in the area of 1.3 times unity. Personally I don't generally like to see numbers below 1.1 times unity - although there have been cases where I have actually used unity itself - and even some reare cases where we calculated based on less than the unity of a member......... but those are very rare and checked countless times to make certain of our design. The real concrerns for catostrophic failure are generally related to loadings being imposed on the existing structure......... and with that one has to be very VERY careful......... Sincerely, Rod[If you want to exceed easily, use 1/480 for deflection. Beyond such generalities, significant calculations are involved, including three different types of limits, two of which are for catastrophic failures.
Thanks for your post. I was trying to give the OP something that does not really exist, as in an amateur easy to use safety margin.
In my mechanical engineering days I did I beam design for various applications amongst other seemingly unrelated at the time to studio design applications.
Andre
[edit]
To the OP:
Looking over the thread, you are in over your head looking for things that do not exist. Use span tables from your State building code.
That's the information I was asking for: span and available lumber species. Can't use the tables without them, correct? That was my point to the OP.You input the span and the load you want to use - then begin plugging in joist sizes and available lumber species until you find the most economical means readily available to you.
Exactly.To the OP: Looking over the thread, you are in over your head looking for things that do not exist. Use span tables from your State building code.