Occupant Schedule Discussion

[thredge]

We recently looked at implementing the automatic Occupant Load calculation schedule that we found in the following thread where the load is calculated from each room use.

http://forums.augi.com/showthread.php?t=33275&highlight=occupant+schedule

I have a couple of questions or discussion items with issues I have found with the setup of this table.

1.) Gross vs. Net: there are no actual calculations difference for these in the rooms, and no way for it to really do it. Net is what rooms typically take because they don't include the exterior walls or other items per IBC 1002.1 FLOOR AREA, GROSS. In my opinion this can make the occupant load a lot lower than required by the Code.

2.) Calculates per Room: the way the schedule is set up it calculates the occupant load of each room separately and adds that up. In the past I have taken whole departments separated out different uses, added the area of those uses and calculated the loads off the sum of those areas. So I would take a whole department of sleeping rooms and divide by the sleeping room area and round up one person. The by room version takes the area of each room and rounds that result up a person and adds all those room results together. In my opinion this can make the occupant load a lot higher than required by code because it rounds up that one person a lot more than required.

3.) Originally the schedule didn’t round up a person it was just set to round, so we tweaked it to add .49 to each calculated occupant load number and then made that an integer so the totals would add up properly.

So, because I had one concern that might increase the occupant load substantially and had one that might reduce it substantially I took the project I was working on and calculated the load 3 ways to see what actually happened.
1.) By the use per room method.
2.) Translated the use by room method to use by area and drew out my own area plans by uses so I could control the gross and net areas just by how I laid out the area lines.
3.) I took the areas from the area plan and plugged them into my old Excel spreadsheet that I had used in the past to calculate my occupant loads.

The results were:
- For my Excel calculations which I consider to be the most accurate: 380 people
- Revit Calculated by Room Plan: 356 people (24 people short or a little more than 6% error in the wrong direction)
- Revit Calculated by Area Plan: 386 people (pretty close and errors on the side of more people).

My interpretations:
- It seems that not including walls etc in the occupant load calculations is to much for the calculation per room to make up for.
- The Revit Calculated Area plan is pretty close for our purposes, which will save us some time and the table will look like it adds up for the most part.

I’d love to get some other peoples thoughts on this and how they understand occupant load calculations are supposed to be done vs. how people are trying to automatically do them in Revit.

Thanks.

[Justin Marchiel]

i work in British Columbia Canada. I do my occupant loads based per room then add them up as they go to a corridor, then to stairs, etc.

I have found that taking the room area and dividing it by the occupancy per sqm is pretty accurate. however i am doing it room by room so that will reduce any errors. i also have the automatic value as a check and the value in the tag is a manual parameter. this way it forces the user to look at the schedule and compare the values and not jsut blindly add values without checking. computers can do a lot, but i find it important to review values when they impact things like life safety.

Justin

[dbaldacchino]

If the code asks for Net areas, you have to use the room area, correct? So I would not expect to see a discrepancy for such spaces since you just take the room area and divide by the occupant load factor (net) and get a number, which you round up by adding .49 (and make this parameter an integer to avoid rounding errors when adding totals). That's exactly the same thing you do by hand....if you get a value of 27.2, you round to 28,and you add the 28 with the other numbers, and not the 27.2 (this is the reason for the integer parameter).

If the code asks for Gross calculations, then you take the area of the "department" or whatever boundary such as a Business area, which includes walls, chases, etc. and then divide by the Occupant Load Factor (Gross), get a number and do the same to round it up. Again, I don't see why there should be a discrepancy between doing it in Revit this way, doing it in Excel or by hand. There has to be a mistake somewhere, or some issue in Revit that 'm not seeing. Could you post a simplified example and show the discrepancy?

[thredge]

I'm actually located in Iowa in the the United States for reference.

From my understanding net doesn't mean room area, or gross vice versa..we have a nice Life Safety Handbook in the office that has comments in the margines on what you read in the code, and some of those comments about Table 7.3.1.2 are:

"The first column of the table is deliberately headed use rather than occupancy because the use of the area might differ from the occupancy." Also, I don't belive by use they mean room either.

"The gross area figure applies to the building as a whole (the area within the confining perimeter walls of the buildng); the net area figure applies to actual occupied spaces, such as classroom spaces, and does not include the corridors, the area occupied by walls, or other unoccupied areas."

It actually goes on to give an example in the notes where it has a floor of an office building with 2 conference rooms. They take the total area of both conference rooms and divide by 15 sf / person (Assembly - Less concentrated) they then subtract the conference room areas from the entire area inside the exterior walls and divide by Business Use (100 sf / person). So this is the way that I have always done my calculations, not dividing it up by rooms. Just sum of the areas of same use, added together, and calculate the number that way. Then add those up for the different areas.

The IBC in 1002.1 definitions also talks about 'Floor Areas' not room areas, and talks about how wall space, corridors etc...all get grouped into the gross area. As you can see from my results above, the difference can be somewhat extreme if you don't include the walls in the calculations.

I think that because of the size of hospitals and other large projects the factors were always designed to be lumped factors so you didn't have to calculate every room, because prior to something like the scheduling in Revit it would be very time consuming. So the factors have always included adjustments because there would be corridors and walls etc in the areas you start with... included in those calculations.

So, in the end, I don't belive 'net' refers to actual room size. And I know gross specifically states it doesn't mean room size.

Not sure how to do a simplified example, because where this really starts to come out is when you have really large facilities. I'll see if I can find some time to put something together eventually. I'm liking the discussion though. I enjoy finding out how other people think it should be done too because I think I know it, but doesn't mean I'm right either.

In the end though, the important results we are getting behind calculating our occupant loads are:
- to veify rooms, suits, spaces with only one means of egress are less than 50 people.
- to verify that the calculated widths based on those occupant loads of doors etc.. are large enough.

I know in most cases our calculated widths aren't even close to what is required by default door, hallway stair widths...we get close in stairs sometimes in hospitals though.

[dbaldacchino]

Thanks, I agree that's it's a good discussion :)

I have always seen it done a certain way...for exampe we don't total all classroom areas and then find the occupancy from that. Instead, we total the individual occupancy of each space. I think the latter is more conservative (gives you higher occupancies), but in the grand scheme, it shouldn't put you over the top as we always provide more exiting than is required. After all, we just want to make sure we exceed the minimum and not design to be just AT the minimum :)

[aaronrumple]

This is one of those "whoops" things in Revit. They designed the program to work with BOMA and building managers - not codes.

Rooms can be calculated by several different ways under Settings > Room and Area Settings. Unfortunately this is a project wide setting. What Revit really should be able to do is have Rooms report net and gross based on rules that we assign. For instance I might want exterior walls to compute to interior face and interior walls to compute to centerline. We should be able to apply those settings per view - not per project.

What you can do to get better results is set your rooms to calculate to centerline of walls. You'll also have to carefully manage what walls are room bounding and which are not so that the whole floor plate is taken into consideration. Another thing you can do is put rooms in chase spaces and other un-occupied areas. This will yield occupant loads that are on the high side. But better CYA than law suit. You'll be high because Revit is going to calculate the floor to the centerline of the exterior wall - not the "area within the inside perimeter of the outside wall (IBC 1002)". You can adjust for this if you make the exterior walls non-room bounding and add in room separation lines at the right spots. You'll also be high on those spaces that are based on net area - such as classrooms.

I use a key schedule which is really just IBC Table 1004.1.1 and apply the correct function to each and every space which goes pretty quick.

Of course this makes a mess of things when you want to budget net and gross area. So you have to switch room settings back to get the correct usable floor area.

Area plans can be created which give you very good area reports for code, but you are then doing the work twice. Now you have rooms to manage and then areas representing just about the same things on your plan as areas. So you have room names and area names to coordinate. And room numbers and area numbers to coordinate.

Revit really needs more flexibility for both room and area rules. They also need to be able to create islands and nest rooms and areas within one another. And rooms and areas need to link to each other so these two informations sets can provide better analysis.

[aaronrumple]

Thanks, I agree that's it's a good discussion :)

I have always seen it done a certain way...for exampe we don't total all classroom areas and then find the occupancy from that. Instead, we total the individual occupancy of each space. I think the latter is more conservative (gives you higher occupancies), but in the grand scheme, it shouldn't put you over the top as we always provide more exiting than is required. After all, we just want to make sure we exceed the minimum and not design to be just AT the minimum :)

Classroom are done net square footage. So it works there. The stack area in your library is calculated gross - so now you're off on that calculation.

[thredge]

I'll agree with that. That it is the basis for our minimums.

I think my only issue with the room based version is that it is hard to truly separate gross from net. You get the choice under Area and Volume Computations to calculate the room areas to the finished face of walls or to the center of walls. Unfortunatly to the finished face would be great for net and to the center of walls would be better for gross (although some chase and cavity spaces can get left out this way if you don't give them a room without a tag at least.

Just for fun I changed the Area calculation over to center of walls and my occupant load by Room Plan went from the 356 up to 447. So much more conservative, but dang it went from 24 people too short (6% off) to 67 people to many (18% off). So if I do get more area in there the calculating each room first then adding the results really does inflate the number a lot. I just don't think that the buy Room version defined to the interior face of walls is the correct way to do it either way being a smaller number than when including walls. I did look at both codes a little closer and they both state that gross area is the area within the inside perimeter of the exterior walls, so those are some walls that don't have to be counted.

Well, as we said, it is a ruler for safety, as long as the code official agrees with the way we are looking at it, we should be OK.

The funny thing is I know some Architects that just look at the building as a hospital, divide the whole area by sleeping areas or outpatient treatment areas and get a number that is substantially lower than if they factor in all the conference rooms and break rooms and waiting areas as assembly spaces, and they have gotten that to fly with the officials I guess.

[thredge]

That was beautifulty put, AR. That would be the perfect solution, I suppose I could control things a little better with room separations and adding rooms inside walls where I needed net areas. As you can see my number got a little crazy when I set rooms to center of walls, but that was more because of the calculate each room first and add second.

In my mind I need one more choice in the schedule to calculate calculated values per schedule setup and totals also...so if I don't Itemize every instance it wouldn't do the math that way. A check box per calculated value would work great for that because it isn't actually calculated in the room or area it is calculated in the table anyway...the choice would just change how it was calculated.

Just a thought.

[Dimitri Harvalias]

My approach is this:
Areas for finishes and Finish schedule calculations - use the room objects and the areas they report. If set to inside finish face they are by design, NET AREAS i.e. they wil not include walls, columns etc.
Code calcs, gross areas, any 'real' calculation - use area objects and a variety of area schemes. Boudary liens can be placed where they are need for each calcualtion. Whether by department, room, floor leve, use... they will always report actual areas. I add parameters to allow filtering of what is inlcuded in calculations or not included (for example, elevator shafts are not included in Gross Floor Area calcs in some cities, they are in others)

Regardless of whether you calculate your room areas to center of walls or inside face of walls you will never get an accurate 'overall' area because Revit will not factor in the half of the wall at the perimeter fo the building. Not significant in a two storey house but could be in a six level airport that is 1.5km long!

[thredge]

Exactly.

Now comes our dilema, which version do we put in our template. Because without doubt the room one is simpler and more straight forward, but the area version is more accurate and better when you are aiming at that 50 person single exit space, or that existing stair is really close to not being wide enough for the existing building and the addition you are adding.

[Dimitri Harvalias]

Why not both? They have completely different functions. At the preliminary stage use the area plans and area sched. Once exiting and other critical code related issues are established then you start adding the room specific information for room and finish scheduling.
The other alternative is to create both and store them in a 'schedule template' project. Each one can be brought into a project as required.

[dbaldacchino]

Thanks Aaron, very well put and I agree. For total flexibility you'd want to have each room area be calculated per user preference independent from the gloabl setting. Not sure how many would like that function (you know....too many overrides?).


The stack area in your library is calculated gross - so now you're off on that calculation.

I might be missing something and I want to make sure I don't. Why would I be off if I use an Area plan for this situation, where I outline exactly what my boundary is? I'm saying:

Use Area Plans for Gross calculations so you can outline the exact extents of the area in question since you cannot do that accurately with rooms;
Use Area Plans for areas that require Net calculations in which only part of the room area needs to be considered (so I can outline the exact extents I want).To clarify, in our projects we always calculate areas to the inside face of finish when checking compliance with our programs and when calculating occupant loads for individual spaces (net).

[Justin Marchiel]

doing public schools is easy for us because the teachers union mandates that a classroom can never have more then 30 students, so the occupant load in never higher then 31. the only places we need to calculate values is gyms, and auditoriums.

Not really adding the to the question, just adding some twist after a long day in the trenches!

Justin

[aaronrumple]

doing public schools is easy for us because the teachers union mandates that a classroom can never have more then 30 students, so the occupant load in never higher then 31. the only places we need to calculate values is gyms, and auditoriums.

Not really adding the to the question, just adding some twist after a long day in the trenches!

Justin

Whoa! Not buy code. Just because the teaches union says no more than 30 students, doesn't mean the occupancy of the room per code is 30. 30 x 20 SF net = 600 SFAny classroom sized over that would have the wrong calculations. A typical class room for 30 students is more like 800 SF min. That puts every classroom off by 10 students as far as the code is concerned. Now, you're not likely to mess up the exiting from that specific room - but you're calculations for overall exiting are way off.

Better check your liability.....

[aaronrumple]

Why not both? They have completely different functions. At the preliminary stage use the area plans and area sched. Once exiting and other critical code related issues are established then you start adding the room specific information for room and finish scheduling.
The other alternative is to create both and store them in a 'schedule template' project. Each one can be brought into a project as required.

Clerical errors and time.

This means doing things twice. And then manualy entering the data in two places and transfering it all to a central list - for which Revit doesn't have a good method.

And since most firms have a life safety plan these days - it means drafting the info in - not letting Revit do the calcs.

[aaronrumple]

I might be missing something and I want to make sure I don't. Why would I be off if I use an Area plan for this situation, where I outline exactly what my boundary is? I'm saying:

Use Area Plans for Gross calculations so you can outline the exact extents of the area in question since you cannot do that accurately with rooms;
Use Area Plans for areas that require Net calculations in which only part of the room area needs to be considered (so I can outline the exact extents I want).To clarify, in our projects we always calculate areas to the inside face of finish when checking compliance with our programs and when calculating occupant loads for individual spaces (net).

Area plans can indeed be used. The rentable is all that is needed, since it places the area lines at the inside of exterior walls and this corresponds with IBC's definition of gross floor area. For rooms that must be calculated net - you can manually place the area separation lines in the correct location. However, it means that you have to make each room and area. So it is an enormous amount of duplication of effort on a large project. If I change a room number or name - I also have to update the "area" room number and name. If I add in more rooms, I have to manually go back and add in more areas. It is just tedious for something that should already be there and automatically update.

If you're using net area in all your calculation - your not following code, and coming up short on your egress units.

[dbaldacchino]

Thanks Aaron. I'm gonna put a simple example together and post it, mainly to highlight where the current tools fall short and perhaps make a good case why the Space" tools available in MEP would be a solution to this (or maybe the "zone" tool, where you can aggregaret a bunch of spaces into being one "space", such as "Business" etc.).

[aaronrumple]

I submitted a wishlist item for a Code Based Area plan with my thoughts on how it should go... I'll post the link as soon as it is on AUGI.

[dbaldacchino]

Cool, I'll take a look at your submittal.

I'm attaching an example project (don't critique the design lol!). I can see where doing Area plans for Gross calculations could still lead to rounding errors because you cannot perform calculations on TOTALS, but it has to be done on each area and then totaled at the end.

[Steve_Stafford]

RME 2009 has Spaces and Zones and Zones "know" about Spaces! When I saw this I have to admit being frustrated since I've been asking for Areas to become aware of Rooms since I started using Revit. I don't want to add heat to the whole feature overlap issue but RME does keep getting functionality that RAC users have wanted for a long time...similar issue we were having with RST in the recent past as well.

One other comment...codes...why can't they be "simpler". People seem to prefer to construct obtuse rules for everything. A person can't occupy the space in half a wall. A person can't occupy space over a counter, but then you'll have some "standing and climbing room only" event in a school where kids are standing on counters and a fire breaks out and somebody gets hurt or killed trying to get out...in response we get new code calculations to prove our designs are safe.

Then you have the building code overlap with school construction administration organizations rules.

Landlords want to charge for half the wall and the air breathed by a tenant...

Ugh!! (sorry, not contributing...just venting!)

[dbaldacchino]

Haha I feel ya....codes are the most important part of the practice of Architecture (life safety is what's mentioned in our license declaration!), but to me they're the most boring and driest part of the process! I know some people that are absolutely passionate about them and know every little exception and rule known to man. There are however tons of misconceptions raised because of the different rules between codes, tenant calculations, etc. (here's another one Steve: plumbing counts). Gotta love it :screwy:

[thredge]

Cool, I'll take a look at your submittal.

I'm attaching an example project (don't critique the design lol!). I can see where doing Area plans for Gross calculations could still lead to rounding errors because you cannot perform calculations on TOTALS, but it has to be done on each area and then totaled at the end.

This is what I was trying to comment on earlier, when I said I was turning off the itemize every instance in the schedule. As I said though, on about a 30,000 SF project I ended up with a total 386 occupant load because of multipule storage spaces etc... instead of the 380 that I got if I did the same thing by hand. So the area plan version isn't to far off because their usually aren't as many multipule spaces as there were rooms of the same occupancy.

I still feel the room plan to the finish face of walls is to far in error the wrong way to really use, but for the quick version using rooms to the center of walls is a little better, but it is quite a bit above and beyond, being at 447 instead of 380. I belive that all of my exits and occupant widths would have been the same though, I think in some of my single exit areas though it pushed the load to a little over 50 however.

[thredge]

Why not both? They have completely different functions. At the preliminary stage use the area plans and area sched. Once exiting and other critical code related issues are established then you start adding the room specific information for room and finish scheduling.
The other alternative is to create both and store them in a 'schedule template' project. Each one can be brought into a project as required.

We probably will use both, but I don't think we can quite do it like this. We will probably use the room method to the center of walls for smaller projects where we aren't to worried about the occupant loads blowing up a little bit. For a mor accurate take we will probably just got with the area method to try to be more accurate. Some projects may require changing from the room method to the area method to be more accurate with our single egress spaces and exiting widths when required. Also, some hospital facilities we work on should probably just use the more accurate area method because we have to pull old code reviews and occupant loads when we do additions or renovations and I know that is when we get tight with widths and things.

[thredge]

Whoa! Not buy code. Just because the teaches union says no more than 30 students, doesn't mean the occupancy of the room per code is 30. 30 x 20 SF net = 600 SFAny classroom sized over that would have the wrong calculations. A typical class room for 30 students is more like 800 SF min. That puts every classroom off by 10 students as far as the code is concerned. Now, you're not likely to mess up the exiting from that specific room - but you're calculations for overall exiting are way off.

Better check your liability.....

I think the point you were trying to get at, Aaron, is that the code requires you to do the calculations per their load factors and compare it to what you are already using, and use the larger of the numbers. It basically says that at the front of IBC's chapter 10. It also allows you to increase your loads to whatever you want them to be as long as you provide exiting as required for that load.

That brings me to another question on the Revit tables then. Is there anyway to input manual numbers when you are dealing with those loads like the Bowling Center for Example, where there is basically some manual counting work you have to do and add in?

We would like to place the table on our code review sheet for the code official, but that is one more issue I don't see an easy way around. Not that we really do a lot of Bowling centers though.