Question on supplying fresh air to unoccupiable spaces

Hello! 

You understood correctly - ASHRAE 62.1 defines at which spaces you must supply fresh air, and how much exhaust you must provide from certain spaces. 

If you want to provide more (more air to occupied spaces than required by ASHRAE 62.1 if you want better air quality or local standards are stringent, or fresh air to any unoccupiable space) - no one can stop you from doing this. 

Consider that more air supply (also at unoccupiable spaces) would make more electricity demand in project building at energy modelling, since baseline building provides air per ASHRAE 62.1 requirements. 

Acording to ASHRAE 62.1 (and for purposes of ASHRAE 62.1) there is no definition of unoccupiable space. There is only definition of occupiable space:
 

occupiable space: an enclosed space intended for human activities, excluding those spaces that are intended primarily for other purposes, such as storage rooms and equipment rooms, and that are only occupied occasionally and for short periods of time.

So unoccupiable space is any space that is not fall under definition of occupiable. As the definition of occupiable space provides a clue what is an unoccupiable space (storage rooms and equipment rooms, and that are only occupied occasionally and for short periods of time) at our projects we considered for ASHRAE 62.1 purposes as unoccupiable a premises or a part of premises where:

- no stationary working places are provided, and

- at regular site activity people can occure at such space for short periods of time (we considered it as less that an hour) for routine tasks like maintenanse or adjusting some equipment or other, and 

- in routine it unlikelly that it would be more than two people simultaneously. 

For instane: lobby / corridor has no working places, but people regularly occure there, so it's occupiable space in terms of ASHRAE 62.1. Janitor closets (but for it there is minimum exhaust rate per table 6-4 of ASHRAE 62.1), mechanical rooms, equipment charging rooms (in some cases it also must have exhaust) etc. - are not occupiable spaces. 

Just note, that for other standards, for instance - ASHRAE 55 occupiable zone has different definition:

zone, occupied: the region normally occupied by people within a space, generally considered to be between the floor and 1.8 m (6 ft) above the floor and more than 1.0 m (3.3 ft) from outside walls/windows or fixed heating, ventilating, or air-conditioning equipment and 0.3 m (1 ft) from internal walls.

So, corridor would be occupied zone per ASHRAE 55, but not per ASHRAE 62.1. There is also light issue - some zones are considered as an unoccupied for daylight calculations (like here https://leeduser.buildinggreen.com/forum/regularly-occupied-area-hotel-room).

The Indoor Environmental Quality overview section within the LEED reference guide provides a comprehensive explanation for how to define spaces within a building. 

It helps to provide a narrative when submitting the LEED application. My 'template' narrative includes the following:

REGULARY OCCUPIED = spaces that you would expect to spend most of your day. (e.g., office)

NONREGULARLY OCCUPIED = space that you would expect to occupy for one hour or less. (e.g. break rooms, corridors)

UNOCCUPIED = space that you would never expect to occupy. (e.g. mechanical rooms, emergency egress, inactive storage)

UNOCCUPIABLE = space you cannot walk into. (e.g., walls, mechanical shafts, etc.) 

it is common that the terms "unoccupied" and "unoccupiable" are used interchangeably. It is my understanding that these are two differant types of space within a building. 

We also note that rooms that require continuous exhaust (e.g. restrooms, janitor closets) are also excluded from the vent calcs. 

This approach has been successful when explaining to GBCI why the gross floor area listed within the Details tab of LEED Online will not match the total floor area listed within the vent calcs. (also, Gross Floor Area listed in the Details tab is measured from exterior faces of walls, while vent calcs are measured from the interior faces of walls)

Hope this helps!

Actually, in terms of table 6-1, it's not divided in regularly/nonregularly occupied spaces. Just for some spaces airflow is calculated only per area, not per area + default occupancy. So such division can take place, but it's not really nececcary, otherwise such division is required for other purposes. 

I preffer not to do so, since separately any persone can spend at some palces (like corridor) less than hour, but at every moment it can be some people at corridor.

Can bу done table with list of all premises and columns with checkboxes is that premis occupiable or not per ASHRAE 62.1, ASHRAE 55, Lighting calculations, etc. It would take top 3-4 hours with mechanical engineer, approve it by the client - it would be helpfull for long time.