2015 National Building Code
9.10.4.4. Roof-Top Enclosures
1) Roof-top enclosures provided for elevator machinery, stairways or service rooms, used for no purpose other than for service to the building, shall not be considered as a storey in calculating the building height.
2018 BC Building Code
9.10.4.4. Roof-Top Enclosures
1) A roof-top enclosure shall not be considered as a storey in calculating the building height if the roof-top enclosure is provided for
a) elevator machinery,
b) a service room,
c) a stairway used for no purpose other than for access or egress,
d) an elevator lobby used for no purpose other than for access or egress, or
e) a combination thereof
The difference is:
If you are designing a 3 storey townhouse with a roof top patio and stairway, it will be 3 storey in BC, but 4 storey in other provinces, such as Alberta and Saskatchewan.
Some people think that they can use alternative solutions whenever they want if they don't like the requirements in Division B. The facts are:
1. Alternative solutions are not easy solutions.
It is Division B, not alternative solutions, that sets the minimum standard of the Code. Alternative solutions shall be not "well enough", but "as well as" the acceptable solutions. To achieve the minimum level of performance required by Division B, deviation of one way in Division B shall be compensated by another way in alternative solutions.
2. Alternative solutions are not cheap solutions
To compensate the deviation of Division B, the technology and construction method will usually cost more than the traditional way. Besides this, It is extremally expensive to have a detailed fire analysis and modelling when preparing alternative solution itself.
3. 99% of alternative solutions are not required
It is not hard to comply with the requirements of Division B. Unless you are encouraged to try a totally new construction material or technology which is not covered by Division B, alternative solutions are not required. Something must be wrong if you think you need an alternative solution.
4. Professional’s opinions are not acceptable alternative solutions.
Every professional is an expert only at his own professional area. An architect is an expert of building space and appearance; a structural engineer is an expert of structural design. One of their responsibilities is to comply with the code, not to make the code. Their opinions are not alternative solutions recognized by the Code, unless evidences are provided to prove their solutions are equal or better than that required by Division B.
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