How to determine building height of storage garage considered as a separate building

[sunyaer]

This is from Ontario Building Code (NBC is similar):

3.2.1.2. Storage Garage Considered as a Separate Building
(1) A basement used primarily as a storage garage is permitted to be considered as a separate building for the purposes
of Subsection 3.2.2. and Sentences 3.2.5.13.(2) and (3), provided the floor and roof assemblies above the basement and,
except as permitted by Sentence (2), the exterior walls of the basement above the adjoining ground level are constructed
as fire separations of,
....
------------------------------------------------------------------------

I've seen architectural design following this path:

1. Determine if there is a need to considered a basement storage garage as a separate building;

2. If yes, calculate the floor area and number of floors of the storage garage;

3. Use the number of floors as number of storey (a defined term in OBC), and area to match whatever from "3.2.2.75. Group F, Division 3, up to 6 Storeys, Sprinklered" to "3.2.2.82. Group F, Division 3, 1 Storey, Any Area, Low Fire Load Occupancy", and apply the requirements for design for the purpose of Subsection 3.2.2.


My question: since the storage garage in question is basement, and basement floor number is not qualified to count for building height ( building height means the number of storeys contained between the roof and the floor of the first storey), so, how to determine building height in order to use Article 3.2.2.75 to 3.2.2.82?

 

[tmurray]

It sounds like we are talking about a situation where the garage is located below grade with the superimposed building located fully above grade.

I would disagree that you do not count the basement as a storey in this case. Building height is a defined term. It is the number of storeys between the roof and the first storey. First storey is also defined as being the uppermost storey having a ceiling not more than 2m above grade. In this case, the first storey is in the basement as there are no above grade stories within this "building". There is a second building superimposed over this one with it's own first storey and building height.

The fly in the ointment is the use of the term "roof" in the building height definition. In this situation, I would interpret the roof of the garage as being the floor assembly separating the two buildings.

In general, you are correct that we don't normally count basements as stories in determining building height, the only exception to this would be where a building has no above grade stories.

 

[sunyaer]

...Building height is a defined term. It is the number of storeys between the roof and the first storey. First storey is also defined as being the uppermost storey having a ceiling not more than 2m above grade. In this case, the first storey is in the basement as there are no above grade stories within this "building". ..

Say, there are 3 storey parking in basement, which storey is the first storey of the basement "building"? And what is the building height of this separate basement "building"?

The fly in the ointment is the use of the term "roof" in the building height definition. In this situation, I would interpret the roof of the garage as being the floor assembly separating the two buildings. ...

Agreed.

 

[tmurray]

Say, there are 3 storey parking in basement, which storey is the first storey of the basement "building"? And what is the building height of this separate basement "building"?

There would only be a single storey (the closest to grade) for the 3.2.2 designation, but see section 3.2.2.15 for details on the construction requirements for this specific situation.

 

[sunyaer]

There would only be a single storey (the closest to grade) for the 3.2.2 designation, but see section 3.2.2.15 for details on the construction requirements for this specific situation.

strict logic in applying the code.

The following table in a drawing is from the internet:

Is this correctly apply the code in respect to storage garage being considered as separate building? (It applies 3.2.2.75.)

https://www.dropbox.com/s/jr2mas182iz6p7w/Storage Garage Considered As A Separate Building.jpg?dl=0

 

[tmurray]

This appear to divide a building into two with a vertical fire separation rather than a horizontal one. See the location of the 2 hour firewall in the spatial separation section of both buildings.

The designer used a two hour fire separation between the storage garage and the remainder of the building, but they may not be considering it as a different building as sometimes there is no advantage to this, particularly when the residential portion is more than 4 stories so NFPA 13R can no longer be used.

The applications I have seen was to limit the use of NRPA 13 to just the storage garage portion, letting the use the less restrictive standard NFPA 13R above it. There may be some other advantages as well that I am not remembering, but this is a major one.