Energy Vanguard Blog

Where Were the Control Freaks!? Suspended Ceilings Are Air Leaks

Posted by Allison Bailes on Mon, Nov 19, 2012

You know how sometimes people ask, "Where were the adults?" In the field of building science, I've got a new question: Where were the control freaks? It's not nearly as well known as it should be, but buildings need to have well-defined control layers to control heat, air, liquid water, and water vapor. Often they don't. What I'm about to show you is graphic and may be shocking to you. If you're easily offended by building science crimes, you may want to click away now.


building enclosure control freak suspended ceiling fiberglass batt insulation yuk

Have you ever seen fiberglass batt insulation on top of ceiling tiles in a suspended ceiling? I've seen it enough that it deserves to be brought out into the light and ridiculed. You don't see it much in homes, but I'm not going to let that stop me because this way of handling a building enclosure is an abomination. See Exhibit A above.

Yes, that's fiberglass batt insulation, poorly installed, as usual. There are just too many obstacles in the way for the installers to get a nice, Grade I installation on top of that suspended ceiling.building enclosure control freak suspended ceiling fiberglass batt insulation heat flow infiltration Just in that first photo, you can see a recessed fluorescent light fixture, sprinkler system, ducts, and suspension wires. To get Grade I, the installers would have to cut and fit the batts perfectly to fill the space above the ceiling completely. And you and I both know that's rarely going to happen.

But the installation of the fiberglass batt insulation actually isn't the main problem here. No, the main building science crime is that they put this air-permeable insulation on top of an air-permeable ceiling. Air-permeable insulation can work fine if it's completely encapsulated on 6 sides with materials that are air-impermeable. It can work OK sometimes when installed in ceilings and not encapsulated on the top. (Yes, there can be problems with that installation, but they deserve an article of their own. Let's ignore them for now.)

One thing you've got to have, though, if you're going to put fiberglass on top of a ceiling is a ceiling that acts as an air barrier. The ceiling tiles in abuilding enclosure control freak suspended ceiling fiberglass batt insulation displaced suspended ceiling don't do that. The material itself isn't the best air barrier, but the worse problem is the framework and the other penetrations (lights, HVAC vents, sprinklers) that aren't air-sealed.

If you're doing a heating and cooling load calculation for the office below that ceiling, how do you model the air leakage? Yeah, you can choose 'leaky' from the simplified inputs in your software, but this ceiling might be even leakier than that. If someone came to us with plans for such a building and asked us to do the HVAC design, I'd tell them to go back put a true air barrier in that ceiling. Otherwise, I won't know how to model it and won't take the liability of making a wild guess.

Air-permeable Insulation + Air-permeable Ceiling

= Building Science Crime

Even worse, that lack of an air barrier in offices like the one beneath the ceiling shown in these photos can lead to health and safety problems.

What's outside that office? A warehouse.

What often runs in warehouses? Forklifts.

What do forklifts do? Make carbon monoxide.

And to make sure you pull that carbon monoxide in and deliver it to the people in the office, you can try the standard trick of having an open return plenum above the ceiling. In other words, leave the return side of the air handler open so it can suck in whatever air it can. If that space is connected to another space with poisoned air, it'll pull it in.

If you're designing buildings with this type of ceiling—or building them or working on them—it's time for you to learn to become a control freak. This assembly does not work. So again I ask, when this building was designed and built:

Where were the control freaks!?


Related Articles

Be a Controlling Building Enclosure Control Freak with Control Layers

How to Grade the Installation Quality of Insulation

An Incomplete Building Envelope Doesn't Work

Building Science 101


Tags: building enclosure, insulation, air leakage