Home office deduction, home square footage

[Clintsdentrepair]

Do I add all structures listed on public records to my total square footage for home office deduction? For example, finished attic (a couple inches short of 6') enclosed porch, detached garage, balcony etc... The more I add the less I get back. 

[MarkVDHtwoO]

I have looked into this also and find consensus that it only includes "living space" which is often defined as having finished floors/walls/ceilings and heated/cooled like rest of home. *SOMETIMES* there is mention of a minimum ceiling height of 7 ft. That is the point that I am wondering about as our cape cod has upstairs bedrooms with 6'6" ceilings. I want to know if that low ceiling space should be counted in the stated area of my home.

[Carl]

Your total floor space of which you claim a percentage as a home office, is based on what is listed as such on your property tax bill. That's the floor space you are taxed on by your county or whatever jurisdiction you're in that assesses property taxes. Period.

[Anonymous]

@Carl.  maybe where you live they have the total floor space on the tax bill but not where I live.  Cook County Illinois.  In Illinois they use assessed value sq footage is nowhere on the bill.  however, the cook county treasurer's office does have sq footage in its records.   in Illinois an attached garage's floor space is included in the home's sq footage even if it is not converted to livable space but not a detached garage which could be converted is not

[Carl]

I picked a random address with a home on it at https://www.cookcountyassessor.com/pin/1013140010000

Scroll down and click on the "Characteristics" link to expand it. Shows me clear as day that property structure has 1,014 square feet of floor space. So that would be the number I use for my total square footage.

[Hal_Al]

I agree with the "living space" definition, which would include the  finished attic (most likely)  but not the enclosed porch (if used as a porch) , detached (or attached) garage,  or balcony.

[AmeliesUncle]

I don't think there is a clear-cut answer.

The Home Office form is deduct a proportionate amount of building (mortgage interest and depreciation), real estate taxes, utilities, repairs.

A "finished" area (regardless of the ceiling height) would definitely be used because that fully contributes to those deductible items.

Unfinished areas, such as a garage, PARTIALLY contribute to the expense of the building, taxes and utilities, but often at a much lower rate than a "finished" area.  So one could argue either way if they should be used or not.

[MarkVDHtwoO]

Thank you all for your input. Clearly not all square feet are equal and that there is a continuum of “finishedness.” It makes sense that agree with tax records. I may explore having taxable square footage meet ANSI standards:  

“Ceiling Height Requirements
To be included in finished square footage calculations, finished areas must have a ceiling height of at least 7 feet
(2.13 meters) except under beams, ducts, and other obstructions where the height may be 6 feet 4 inches (1.93
meters); under stairs where there is no specified height requirement; or where the ceiling is sloped. If a room’s
ceiling is sloped, at least one-half of the finished square footage in that room must have a vertical ceiling height of
at least 7 feet (2.13 meters); no portion of the finished area that has a height of less than 5 feet (1.52 meters) may
be included in finished square footage”

https://www.e-rallc.com/ANSIstandards

[AmeliesUncle]

The Tax Code and the IRS does not care about ANSI standards.

They will look at how much that space contributes to the cost of the home, real estate taxes and utilities.  Finished bedrooms will considerably contribute to all of those, regardless of the ceiling height.