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Arhitectural drawing Levels: FFL vs SFL vs SSL

Jen_C

Hi,

I need your opinion on this item. I had a conversation today with colleagues about which Floor Level is the basis in determining the other Levels in a storey. Is it the Finish floor level (FFL) or the Structural Finish Level (SFL) or the Structural Slab Level (SSL)? Correct me if Iam wrong, FFL refers to the level at the top surface of floor finish. This is where all the building element finish levels are referenced from. SFL refers to the level at the top surface of the floor screeding or concrete topping. While SSL refers to the level at the top surface of the structural slab.

Now, when an architect starts to design a storey, which one do you use as your Floor Level? Is it the FFL, SFL or SSL? Also, whichFloor Level serves as the basis of setting the other levels in a storey? Is it SSL is given first then you figure out the SFL then the FFL or the other way around, FFL is set first then the SFL then the SSL? 

What are your thoughts on this one?  Thanks in advance for sharing.

 
Jan 14, 20 11:47 pm
archeyarch

FFL  

Jan 15, 20 12:02 am
b3tadine[sutures]

Are you asking what is 100'-0" or 0'-0"?

Jan 15, 20 12:18 am
Jen_C

Hi, sorry for the confusion.

Jen_C

Its more like which one os determined 1st the FFL, SFL or SSL. What do you determine 1st when you design and carrying that over to your working drawings?

Non Sequitur

I’m assuming here that FFL includes the thickness of ceramic tile or whatever floor covering. We don’t bother with this and use a top of slab or under side of deck dimension. 


This sounds more like a revit level set up question that a CA one. 



Jan 15, 20 7:07 am
b3tadine[sutures]

Neither do I, as floor finish could change numerous times, and I don't want a hinkey number for my slab, unless we're depressing the slab.

SneakyPete

You'd prefer a hinkey number typed into revit?

Jen_C

Yes FFL is on top of any floor finshes ( ceramic tile, wood flooring, vinyl floor, granite stone, pavers, etc.)

Almosthip7

We use 100'-0" as top of main floor slab.

Jan 15, 20 11:09 am
SneakyPete

This is (in my experience) a holdover from CAD where there would be real problems if a drafter forgot the minus sign for negative elevations. This is unnecessary in a Revit environment and is a sign that your QA /QM department is from the hand drafting / CAD generation.

Almosthip7

Also a sign that the American government messed up when the rest of the world was switching to metric and they failed. Now as a Canadian I must use imperial.......

Bench

As a Canadian I think we're definitely all good with both, no?

SneakyPete

I fail to see how switching to metric would avoid an error involving the minus sign unless metric doesn't have negative numbers?

Jen_C

Canada uses both units. I had to get used to using the hard neasurement from the soft mesurement. I notice Canadians like imperial and converting it to metric. That is why sometimes.I get a 395mm thk wall or 153mm studs.

threeohdoor

TOS is the way to go. FFL is always bound to change and is dependent on too many variables. 

Jan 15, 20 12:16 pm
tduds

TOS is for the Structural drawings. Arch sheets reference FFL. Of course, the nice thing about standards is that there are so many to choose from...

Jen_C

Thanks for the info

Jen_C

Can you ellaborate what are those variables that would affect the design, working drawings or constructability of it?

I've always used TOS on my architectural drawings. Then I give dimensions to things like grab bars as "AFF" - above finish floor. I don't think I've ever used FFL.

Jen_C

Thank you, Donna Sink for the input.

threeohdoor

Variables could be: 1) room function changes, 2) slab depressions, 3) transitions between finish material, etc. Say a building section drawing cuts through multiple finish types, does adding 4-5 spot elevations clarify or confuse the reader? Can that info be presented better elsewhere? As Donna alluded to, the more detailed the drawing, the more "real" the dimensions. In our sets, we use TOS throughout as the benchmark (plans, sections, elevations) and then reference "AFF" to indicate hold dimensions for ADA things, etc.

SneakyPete

Are you the architect or the structural engineer?

Do you need the fixed level to be the surface that's walked on or the structure that holds it up?

Do you want the level in the model to provide the element least likely to move?

Do you want your contractor to need to do math?

Make a decision. There is not right or wrong. If your priority is FFL, use FFL. If your priority is making the contractor not have to think, use SSL.


My opinion is that we're architects. We care about the finished building. We also work with dozens of intelligent, capable humans who are responsible for their own various portions of the project and don't need crutches. Use finishes for dimensions and make damned sure your details, schedules, and assemblies are dimensionally correct and provide enough information to eliminate possible RFIs.

Jan 15, 20 12:54 pm
Jen_C

I totally agree with you. I am an architect. For me, when architects do their designs and working drawings, I always think about the 3 items - design, conteact docs and workmanship/constructability. I hate it when architects/ designers tell me that we can make correction or notes on shop drawings to figure out the proper details. Unless the contractor proposes an alternative detail due to site conditions or work around to make the detail more effective or simplifying the details, I find correcting details on shop drawings is a waste for effort and
resources.

atelier nobody

In my experience, whatever we call out, the Contractor actually uses the top of slab as his reference, for everything from floor-to-floor heights to door heights. Based on this, I try to note the drawings clearly that way, and reserve any reference to "finish(ed) floor" for details where it actually matters - then make it very, very clear on the detail that I am pointing to the floor finish, not the slab.

Jan 15, 20 2:38 pm
SneakyPete

And if the contractor was on the design team I may give half a shit. ;)

Jen_C

@SneakyPeteI believe you are refering to "those" contractors. Dealt with them before. Bad habbits, or shall I say, Bad practice dies hard. @atelier nobody, I think there's a grey area to adding notes on shop drawings or submittals. In the door or window schedule, we always indicate the size of the item. And if the wall section and interior elevations shows SSL or SFL, the builder and the supplier will give you according to whatever information that is in the contract docs. A change in dimension due to the point of referenece during installation usually ask a change directive. Notes on shop drawings are only additional comments to the contract docs and usually a cause of many e-mails
during CA stage.

Jen_C

Thank you everyone for your comments. This conversation came about  when I had a kick off meeting  with our team lead. I wanted to find out how he wanted to show the Architect's intent in the drawings so everyone are on the same page. My role in the team was to help out with the production of drawings. 


Anyways, this is why I posted this item here to see what is the industry standards here in Canada or US. As the Design Architect or technician, we should be able to communicate or translate the design to working drawings where it would show the clear intent of the design to the persons who are building it. Be it in Revit or CAD or manual drafting. 


In past, I've always used FFL (top of the floor finish) as my point of reference to determine the SSL or the underside of joists. I do not even bother thinking about the SFL. This has been my practice and have seen some architects, GC, CM and PM do the same.  This process may be different with wood constructon but, most of the time, it can be applied as well.


 From my understanding, why FFL is always the point of reference in a storey is due to the following design reasons:


1. Architects mostly deals with the design. How the whole structure interior and exterior would look and function. Also, someone told me, Architects lead the consultant team, therefore, its always the Architect (responsible for the finishes) will dectate the reference based on the top of the any finishes.


2. All of the code requirements regarding minimum and maximum heights and clearnces are based on the finishes and not from the SSL ( Top of Slab) or SFL (Top of floor screeding or concerete topping). An example for this one are the handrails, guard rails, door heights, finished ceilung height and headroom clearances. If all minimum clear heights are reference from SFL or SSL, how would you comply to the minimum requirements when there's about a 25mm difference between the SSL and the FFL? How are your door panels going to look? Are the door panels going to have various heights due to different floor finish thicknesses while maintaining the industry standard gap requirement for doors? A ceiling height of 8' is not a true 8' at a granite floor finished area compared to the ceiling height at the exposed cement finish area.


3. For me, all floor finishes must be at the same level to eliminate awkward transition strips or ramps between 2 different materials. Unless, design requires an area to have a lower FFL than the rest such as the shower area, utility rooom, etc. A good example are the hotels or condominium. Did you notice any transition strips between 2 different materials? Screeding or concrete topping or mortar or substrate usually accommodates the difference between the structural slab and the floor finishes. The structural slab usually is at the same level throughout except when required to have a drop in level due to drop in FFL or due to structural.design.


Overall, the purpose of this post was to find out if there's a "set-in-stone" rule or standard that architects should follow when it comes to "which goes 1st" when indicating your levels (FFL, SFL or SSL); and to know the different reasoning behind it.





Jan 16, 20 2:05 am
Non Sequitur

This wall of text creams to me: "lack of construction experience".

You need to consider the sequencing of construction when establishing your levels. Structure will always come first since it gets installed before the finishes - obviously - so you can't expect your formwork trade or carpenter to check your finishes schedule to gauge the thickness of finish. It is your responsibility as the designer/architect to ensure that once your finishes are installed that the resulting space is acceptable and coordinate with your structural consultants accordingly.

Chad Miller

creams to me?

Non Sequitur

^Ha...

Jen_C

I agree that the Structure gets built 1st before installing the finishes. True, the surveyor who set the levels in the site, sets his point/ stakes based on the structural levels but this is not the case in design. When you start a design and putting that in working drawings, architects use FFL as the basis in designing a structure structure or the interior space.  Thus the architects level usually sets what the SSL should be and this will be reflected to the structural drawings  where the surveyor uses in staking out.


FYI, I am very well versed with the processes in constructing a building as I've worked for a GC doing a design-build for years before I join the Archi firm; and took part in planning and execution of various trades from the start of the construction up to the turn-over of the project. So far, that has been the process I've been working on site and in the design office.

SneakyPete

Non Sequitor also steals all of the contractors calculators before they start.

Non Sequitur

Jen C, the assumptions you've stated are not typical as I, an architect well versed in design and construction admin, never start any design as you've stated.

SneakyPete

Yes, your assumptions, based as they are in your experience, are not typical whereas Non's, based as they are in his, are typical. See the difference?

Non Sequitur

^Hey now... don't take away our fun


Jen_C

@non sequitur, I worked as a CA also :) so are you saying that when you determine the bldg 1st floor level from the street level ,as required by code, you basically used or reference with SSL? And if it gets finished with 25mm thk finish, what happen to your compliance? It is something I have to get used to.

RickB-Astoria

Architects may use a variety of reference points for elevations but I will reference the work of an architect dating back to 1909-1911 time-frame. I'll later post links to PDFs to such drawings. Work reference: Astoria High School (Astoria, Oregon) by J.E. Wicks (John Erik Wicks). On sheet #6 is an elevation of a three story school building. The elevation references the elevation above sea level datum and site and building elevations levels are likely established using an already surveyed elevation marker. Now, the building references the grade of gym (lowest level of the ground level) floor at an elevation of 239'.00 (yes, the elevation level was done in decimal for the fraction of a foot above sea level datum). This may make sense as this would be computed off the surveyor topographic profile. The second floor which on the plans was referred to as first floor based on the practice of (ground, first, second, etc.) convention. Here is how J.E. Wicks referenced the elevation of the "first floor" (second floor level) ---- Top of first floor joist 256'.625. You notice that it referenced from the top of the floor joist NOT the sub-flooring or the top of furring strips that maybe between the sub-floor and the finish floor. This detail is outlined in the more detailed sections of the building. The longitudinal section of the building is on sheet 10 in the set. Now, don't get caught up on the sheet numbering conventions. When it comes to the concrete slab, it was computed from the top surface of the slab as finished now, of course, you may have a layer of linoleum. So that slab would be raised from 239'.00 (in the example) to maybe ~239'.010 based on thickness of tile and the adhesive. Now, what if the linoleum tiles were changed to 3/8" thick stone tile with a 3/8" cement grout. That concrete slab finish elevation surface would now be 239'.0625 or 239'.063. In the case of the slab, the grade was based on the top surface of the slab not any kind of surfaces that maybe laid on top because even such slabs can have furring strips applied and a finish floor laid over the top changing the finish level elevation. As you will notice on the floors above, the elevation was referenced off the top of the floor joists. More detailed information on the construction of the floors are found in section drawings and in structural details. J.E. Wicks conveniently had just the needed detail on the sheet with the longitudinal section through the building. As you may notice, the floor elevations used actually is referenced is on an "above sea level" basis.

Non Sequitur

Jen, floors don't have to align to street level. We have grading plans and landscaping that bridge the gap between finished floor elevation at the door threshold and whatever elevation the sidewalk (for example) is at. You can't expect that level of precision.

I hear you Non, about sequencing, but: I always give horizontal dimensions to FACE of wall not structure, because I care about the finish space/clearance and I figure the contractor is better at subtracting gyp board thickness/stud actual dimensions than I am as s/he uses them all day.

Chad Miller

We actually have the opposite view Donna. We dimension to face of stud (top and left) in new construction because the contractors suck as doing math.

Non Sequitur

Donna & Chad, I do both (C/L of stud in my case), depending on what I'm trying to convey. Our GC actually get super pissy when dimensions are not to grids tho.

RickB-Astoria

what f---ing grid.... you get no stinkin' grid. It's not graph paper after all... (joking).

Chad Miller

Dims to interior grids are an odd thing. In new construction they can be really helpful to establish a base line to measure from. Exterior grids can be a PITA to measure from in the field. I say we make a surveyor come in a plot all the corners of the stud walls. 8-)

Jen_C

@non sequitur, sorry for the confusion. What I meant was if the 1st floor is a few mm higher than the street level ( being the datum point or the reference grade . I think there's a certain distance from street level/established grade to the "1st storey" level to call it 1st Storey according to the bldg code. I think it was 2m max above the established grade.

Jen_C

Anyways, based on the established grade, you measure your 1st Storey floor level from the established grade to SSL? As for the acceptable tolerances, there is a level of precision that the Architects expect from the contractors. In the construction industry, it is usually 6 to 10 mm difference from the original level. Some countries who use 13mm as an acceptable tolerance in construction.

Jen_C

@Donna and Chad, for interior fitouts, I use the finished wall to finished wall dimension like Donna. The reason being is that, in the case of interior partitions, I like to show the required interior clearance of a room or required clearance of a corridor. On the other hand, for new constructon, I do both - CL of stud and show finish to finish wall dimension for areas where certain clearances are required.

Once again, tduds for the win.

Jan 16, 20 9:59 am
Chad Miller

This has been an interesting thread.  The few firms I've been with it's always been FF at 100'-0" and it referenced TOS.  

Jan 16, 20 10:09 am
tduds

We geolocate our Revit models & so FF is at whatever it actually is above sea level (aka Survey Point. Project Base Point usually puts Level 1 FF at 0'-0"). 

100'-0" is a vestige of the CAD Old Days. Time to let it go.

Chad Miller

We do the exact same thing as you do, we just use 100'-0" as our base elevation callout. I have no preference in what way we call the base elevation out - I see positives and negatives in using both. I will say that I've seen drawings as far back as the 30's use 100'-0" as the base elevation. It's not necessarily a vestige of the old CAD days. 100'-0" was used way back because it was more readable and 0'-0"

SneakyPete

It was used so that if the minus sign was forgotten or missing, there would be no issue. BIM cannot forget the minus sign and few sets are reproduced via photocopy, so degradation over multiple duplications is not really an issue.

Chad Miller

Makes sense why I've seen it with the 100'-0" base elevation in drawings over 90 years old. Those old reproduction methods could miss a lot.

Jen_C

I agree that the Structure gets built 1st before installing the finishes. True, the surveyor who set the levels in the site, sets his point/ stakes based on the structural levels but this is not the case in design. When you start a design and putting that in working drawings, architects use FFL as the basis in designing a structure structure or the interior space.  Thus the architects level usually sets what the SSL should be and this will be reflected to the structural drawings  where the surveyor uses in staking out.


FYI, I am very well versed with the processes in constructing a building as I've worked for a GC doing a design-build for years before I join the Archi firm; and took part in planning and execution of various trades from the start of the construction up to the turn-over of the project. So far, that has been the process I've been working on site and in the design office.



Jan 16, 20 10:09 am

Just to add a little seasoning: dimension RO or center of opening?

Jan 16, 20 8:54 pm
Jen_C

RO for me. While I get it why some uses the Opening CL.

Chad Miller

RO for me too. We don't to much residential work.

Center.

Chad Miller

Donna, do you do a lot of wood framed construction?

peijunfei

Idk why so many F to confuse ppl, if is not too complicated project, I just do:

FFL/T.O.F.F:finish floor level, top of finish floor

T.O.SLAB: self-explanatory

T.O.STEEL/B.O.DECK etc to describe structure.

and B.O.CEILING and so on...If still confusing, check the AIA handbook, I remember there is a cad drat standard something. Remember the drawing's purpose is to clarify not to confuse ppl. They will be handed to client, contractor to read and bid and build.

Jan 16, 20 10:42 pm

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