I have learned that for zoning purposes, building heights in chicago are not measured to the highest point of the building, but from grade to the low end of the highest floor’s ceiling joist. I am curious about the specifics of what is allowed beyond this limit.
Some background:
Over the past months as I walked to the El each morning I enjoyed passing a new townhouse under construction and seeing new progress each day. I am the sort of person who reads Straight Dope and wikipedia a lot and I enjoyed comparing facts I learned online about different building and design considerations to what I was observing each day as I walked past this house. The new house is about a tenth of a mile from the Wellington El stop (but not too near the tracks), in the historic “Terra Cotta Row District”, and flanked on both sides by 3 story + partially-above-ground-basement townhouses, so I assumed for all those reasons that this must be a very expensive piece of land and that I would be treated to seeing a high end townhouse under construction. I was surprised when I saw them capping the walls after only 2 storys.
This of course got me interested in zoning heights and what is allowed.
I have learned that most of my street is zoned “RS3” which allows for a 30’ height limit. It appears that many of the townhouses on my street, about half of which are 3 stories tall, are old enough to have been grandfathered in at taller heights that wouldn’t be allowable for new construction today.
I also learned, to my great interest, that heights aren’t measured to the highest point, but to the lowest point of the highest story’s ceiling joist (at least for flat roofs, which is what I’m interested in). To me this seems to allow for a lot of leeway as to how high the eventual building will be. For example:
-What are the limits on the roof structure above the ceiling of the “top story”? Is there a limit to how high the roof structure can be?
-What are the limits on the “fences” or “guardrails” around the top of a lot of townhouses where it looks like they have rooftop decks? I see that they might be referred to as “parapets” in zoning regulations but I am not familiar with that term as used to describe guard rails.
-I see trellises on top of a ton of townhouses, and I found that in zoning regulations they are limited to “not exceed 11 feet in overall height or extend more than 8 feet above the building parapet, whichever is greater”. So what if I wanted a really tall trellis, would I have to build a tall guardrail to allow for this?
-Why do none of the trellises I spot I rooftops have vines growing on them? Isn’t that the point of a trellis? Is it not allowed?
- I saw that enclosed stair landings and “elevator penthouses” are allowed above building height as long as they “do not exceed 9 feet in overall height or extend more than 5 feet above the building parapet, whichever results in a lesser height”- do they mean exceed 9 feet above the zoning height (e.g. 30 foot RS3 zoning would allow for stairway enclosures to span to up to 39’ above grade) or do they mean that from literally the floor of the rooftop stairway enclosure up to its topmost point, it may not be more than 9 feet? What is the latter interpretation of that regulation if even a 15’ rooftop stairway enclosure could result in a lower overall height than a 9’ enclosure on a taller building in the same zoning?
Finally, one source I read about RS3 zoning relates that it allows for a basement where more than half is below grade plus 2 storeys. (Zoning FAQs – Roscoe Village Neighbors) Why only two stories? Why not 3? Isn’t 30’ tall enough to accommodate a 3 story building, especially with how building height is only measured to the bottom of the top ceiling joist?
