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Measuring stories above grade plane

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nealderidder

Sawhorse
Joined
Dec 7, 2010
Messages
394
Location
Sacramento, CA
To determine building height in stories (for chapter 5 of CBC) you measure from grade plane to roof. If you had a five story building (4 floors of "B" with an A-3 roof deck on 5) and the first story was half "buried" is it possible to call this a 4 story building for chapter 5 or maybe it's a 4.5 story building?

Seems pretty fishy but the term "grade plane" must be in there for a reason right? Grade plane is the average ground level adjoining the building at the exterior walls. In this building I've got an at-grade entry at the second floor to the north (right) and an at-grade entry at the first floor to the south (left). The east and west grade goes from 1FL to 2FL as shown on attached.

Let me know what you think.
 

Attachments

  • bldg height.pdf
    114 KB · Views: 17
The building height in feet is measured from the grade plane to the average height of the roof. The building height in stories is based on the number of stories above grade plane. A story is considered to be above grade plane when one of the following conditions exist:
  1. The finished floor of the story is above the grade plane.
  2. The finished floor of the next story above is more than 6 feet above the grade plane.
  3. The finished floor of the next story above is more than 12 feet above grade at any point around the perimeter of the building.
 
RLGA said:
The building height in feet is measured from the grade plane to the average height of the roof. The building height in stories is based on the number of stories above grade plane. A story is considered to be above grade plane when one of the following conditions exist:
  1. The finished floor of the story is above the grade plane.
  2. The finished floor of the next story above is more than 6 feet above the grade plane.
  3. The finished floor of the next story above is more than 12 feet above grade at any point around the perimeter of the building.
Click to expand...

So if the floor-to-floor from first to second is more than 12' then I count 1FL as a story. Well crap. I think #3 applies, the 2FL is around 14' above grade at one point.

Where did those conditions come from?
 
nealderidder said:
To determine building height in stories (for chapter 5 of CBC) you measure from grade plane to roof. If you had a five story building (4 floors of "B" with an A-3 roof deck on 5) and the first story was half "buried" is it possible to call this a 4 story building for chapter 5 or maybe it's a 4.5 story building?

Seems pretty fishy but the term "grade plane" must be in there for a reason right? Grade plane is the average ground level adjoining the building at the exterior walls. In this building I've got an at-grade entry at the second floor to the north (right) and an at-grade entry at the first floor to the south (left). The east and west grade goes from 1FL to 2FL as shown on attached.

Let me know what you think.
Click to expand...

Grade, decides if you have a basement or not?
 
nealderidder said:
So if the floor-to-floor from first to second is more than 12' then I count 1FL as a story. Well crap. I think #3 applies, the 2FL is around 14' above grade at one point.

Where did those conditions come from?
Click to expand...


Definitions.

You may be mixing up terms.

Decide if you have a basement or not, than start counting stories from there?
 
RLGA said:
The building height in feet is measured from the grade plane to the average height of the roof. The building height in stories is based on the number of stories above grade plane. A story is considered to be above grade plane when one of the following conditions exist:
  1. The finished floor of the story is above the grade plane.
  2. The finished floor of the next story above is more than 6 feet above the grade plane.
  3. The finished floor of the next story above is more than 12 feet above grade at any point around the perimeter of the building.
Click to expand...

with 14'-0" floor to floors and your rough sketch indicating the grade plane around the halfway point between the first and second floor I would say that items #2 & #3 both apply and you have yourself a 5 story building........and some possible trouble with that A-3 occupancy.
 
Tim Mailloux said:
what is the construction type of the building?
Click to expand...

That's what this is all about. If I have a 5 story building with an A3 on top I'll need to be Type 1-A or B there are no other options.
cda said:
Definitions.

You may be mixing up terms.

Decide if you have a basement or not, than start counting stories from there?
Click to expand...


I'm grasping for straws here. The BO isn't going to go for calling my 1FL a basement or a story below grade. Grade along my entire southern side is more than 12' below the 2FL. Time for me to let go...
 
nealderidder said:
That's what this is all about. If I have a 5 story building with an A3 on top I'll need to be Type 1-A or B there are no other options....
Click to expand...

Even if you get the BO to agree this is a 4 story building (it isn't) your still looking at a 2A or 3A construction type with that A-3 occupancy on the 4th floor.
 
nealderidder said:
That's what this is all about. If I have a 5 story building with an A3 on top I'll need to be Type 1-A or B there are no other options.

You can always bring in dump truck loads of dirt and move the grade level up

I'm grasping for straws here. The BO isn't going to go for calling my 1FL a basement or a story below grade. Grade along my entire southern side is more than 12' below the 2FL. Time for me to let go...
Click to expand...
 
So I'm concluding this is a 5 story building. Do I just suck it up and call it Type I-B? No! I beat this horse some more.

If I have 5 stories of use B it's a different ball game. I can do a type III-A, or II-A, and I go from 2 hour floors and walls to 1 hour. Which is a big deal in this existing building. 3/4 of the building is cast in place concrete but a later addition of steel would need to be brought up to 2 hours, which is big damn deal.

So, how do I classify the roof deck as a B? I make it less than 750 SF. (CBC 303.1.2), right?

But I've got 2,040 SF of covered area, it's not all enclosed though. The enclosed portions (VESTIBULE, KITCHEN, STORAGE, BATHROOMS) squeak in at 750 SF. Then I've also got a fair amount of uncovered and unenclosed deck. See attached images.

Could I convince anyone that this roof deck is a B?
 

Attachments

  • ROOF DECK.pdf
    1 MB · Views: 4
It would be hard to convince me it was a B occupancy. 303.1.2 required the small assembly space to be accessory to another occupancy. The entire floor is assembly space, what is it accessory to? With all that seating area (inside and outside) I don't see how you get around the 50 person threshold of 303.1.2 Item #1
 
Tim Mailloux said:
It would be hard to convince me it was a B occupancy. 303.1.2 required the small assembly space to be accessory to another occupancy. The entire floor is assembly space, what is it accessory to? With all that seating area (inside and outside) I don't see how you get around the 50 person threshold of 303.1.2 Item #1
Click to expand...

The B would be accessory to the 4 floors of office space below. This deck is a tenant amenity (not public). But I'm guessing I won't convince you that the open deck shouldn't be included in the floor area of my roof top B occupancy... I keep thinking I only need to count enclosed space when determining floor area of that roof top use but I'm not sure where that's coming from...
 
Tim Mailloux said:
To be an accessory occupancy requires that the space be accessory or ancillary to the main occupancy and that it does not exceed 10% of the area of the story in which it is located.
Click to expand...

I was reading "accessory" in 302.1.2 in the general sense of the word. "contributing to an activity or process in a minor way" not the code defined "accessory occupancy" in section 508.2 but when I say it out loud I'm not even convincing myself...
 
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