• (Edited )

In this case, usable sf is the gross sf. This link may help:

https://42floors.com/edu/beyond-the-basics/usable-vs-rentable-square-feet

Gang Chen, Author, Architect, LEED AP BD+C (GreenExamEducation.com)

• Hi Gang!

Thanks for responding. I understand that in this case, the usable sf is the gross sf, however the question for me is still why and how? Ballast and Problem Seeking both define the difference between net, usable, rentable and gross, so i', confused on why 1) we have to solve of Gross, and 2) Where is gross in R/U equation? =)

• (Edited )

In this case, usable sf = the gross sf.

LF = R/U = rentable sf/usable sf = rentable sf/ gross sf

So,

rentable sf = gross sf x LF

Or use the format in ballast:

A rentable = A gross x LF

Gang Chen, Author, Architect, LEED AP BD+C (GreenExamEducation.com)

• Hi Gang,

Thanks again for taking the time to help me with this. I have a follow up question, why should we assume usable sf = gross sf when they represent two different types of spaces? Whats included in gross sf is not all included in useable sf.  The website referenced above specifically calls out " total square footage' & "useable square footage".

Thanks!

• You are right. I guess in this case, usable sf should be used, and the gross sf should not even be mentioned at all. Otherwise, it’ll just confuse people.

Gang Chen, Author, Architect, LEED AP BD+C (GreenExamEducation.com)

• Thanks for the help Gang. I don't know if it was just their poor word of choice or my lack of understanding.

• Overall space would always be 'gross'.  When the insurance company determines the spaces they need, they are simply adding up the sf of required spaces like offices, conference rooms, and break rooms.  They are NOT adding in sf for hallways, or mech rms, so that needs to be added in. That's the .75 factor.  This problem identifies office plan inefficiency and overall building inefficiency (both are in the normal range too, fyi). The 1.2 building load factor accounts for bldg lobbies, lavs, main circulation, bldg loading dock areas, etc.  Work from inside the spaces, out...  HTH.

• Thanks for the help Rebekka ! I understand the break down, I just think it’s was the wrong choice of term that they used. Gross is clearly defined I. Their chapters .

• (Edited )

I think gross means usable. (see Book Problem Seeking - page 101 or attachment)

• (Edited )

I think in this case, Ballast probably meant “usable sf,” but he might have accidentally used the word “gross sf”, which opened a can of worms. The intent of the question was pretty clearly explained by Rebekka.

Gang Chen, Author, Architect, LEED AP BD+C (GreenExamEducation.com)