What are the metal blocky things on roofs?

January 23, 2009 8:46 PM

What are those blocky, meta-encased things on top of buildings?

Hi. I was on the train today and we are slightly elevated, and I'm passing all these buildings, and I can see their roofs. There are some things that are obvious. For example, there are those vents, that come up, curve around and have an opening. I can only assume they curve around so as to keep rain and snow out. But what are they venting?

But then I see these grey metal things that look like very large boxes. Sometimes there are two of them. Sometimes three. What are they? And how come some roofs have two and others, three? What purpose do they serve?

Thanks to you all.

posted by Sully to technology (10 comments total)

A little hard to tell from your description, but it's probably for air-conditioning.
posted by rhizome at 8:48 PM on January 23

Yes, air-conditioning. They just installed two of those monstrosities on the roof of my boyfriend's building, completely blocking his view of the sky from one window.
posted by kimdog at 8:50 PM on January 23

Besides air-conditioning units (which is the odds-on favorite here), depending on the building, they could also be generators, electrical access boxes, telephone boxes, etc. Really, any number of utility things that are better off outside the building than taking up space inside the building.
posted by Cool Papa Bell at 8:54 PM on January 23

Assuming you mean big commercial or apartment buildings, they might be air conditioning units, electrical boxes, water tanks, or the tops of elevator shafts.

For residences, it's usually just a/c.

The pipes are probably venting the toilets. Bigger ones might be venting kitchen fans.
posted by jamaro at 8:57 PM on January 23

oops, this is the correct link for venting of der terlits.
posted by jamaro at 8:59 PM on January 23

Swamp coolers!
posted by chez shoes at 9:45 PM on January 23

If they aren't HVAC related, I'd suggest that some buildings have really heavy masses on top to counteract swaying..
posted by unmake at 12:16 AM on January 24

Sometimes, cell phone companies use rooftops to put their antennae on. They're 3-foot tall rectangular prisms that tend to look like plastic blocks. They generally face about in several directions.
posted by cmchap at 10:04 PM on January 24

Thanks everyone!
I am not an engineer,
and really was curious.

cheers.
posted by Sully at 2:29 PM on January 25

If you're in New York they might be housing for rooftop watertowers.
posted by chesty_a_arthur at 4:42 PM on January 25