NICE AND EASY: What is a “riser?”

Tall buildings have tall problems. You don’t really think about stuff like this as a homeowner, but if you’re looking at a roof that’s 500 feet above street level, some things have to change.  Your regular satellite TV install isn’t going to work. A big part of that is the sheer amount of wire that it takes to get from the roof to wherever you are.  High rise buildings need special installers with special qualifications.

The riser

Every large building has a big vertical space where all the wires are. It’s kind of like an elevator shaft for cables. This is called “the riser.” It’s specifically designed to let technicians get to the communications cables that every modern building needs. It’s also designed to connect to the equipment closets on every floor (sometimes every other floor.)  The riser is sort of like the main artery of the building. Obviously it’s very important.

The trunk

Sometimes you will hear the riser referred to as “the trunk.” This isn’t a completely inaccurate term. Technically the term “trunk” refers to the master set of cables that travel through the riser, as well as the amplifiers and taps that connect those cables to the rest of the building. If you think about it you can understand how the two terms are sort of interchangeable.

The closet

This term is pretty self explanatory. The closet is the place where all the equipment sits to serve the rooms on that floor. Sometimes a closet will serve two floors, and on some large buildings there are multiple closets. It depends on how much equipment is in there and how much cable runs from the closet to the rooms it serves.

Generally there is at least one “master” closet if servers or special amplifiers are needed, while “intermediate” closets have the equipment that connect to the rooms.

The plenum

It’s a funny word — “plenum.” The plenum is the area above the suspended ceiling and below the roof or floor above. It’s a space where air travels from room to room. A lot of companies will run their cables through the plenum because it’s easy and leads to a clean installation. In some areas you need special cable to meet building codes. I talk a bit more about that here.

Together, the riser, the closets, and the plenum make up the communications infrastructure. They are kind of like the veins and arteries of the body. They are just as important and should be cared for just as carefully.

About the Author

Stuart Sweet
Stuart Sweet is the editor-in-chief of The Solid Signal Blog and a "master plumber" at Signal Group, LLC. He is the author of over 8,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.