If it were a horror movie, I know what they'd be for.

September 26, 2013 11:14 PM

What are these spikes on the ceiling in the parking garage?

In the parking area below my apartment building, there are these spikes on the ceiling. Here's a closeup view.

Any idea what they're for?

posted by Cogito to Grab Bag (11 answers total)

My first thought is that they are to prevent some kind of wildlife from settling in. Birds? Insects? Bats?
posted by Sara C. at 11:23 PM on September 26, 2013 [1 favorite]

Best answer: Perhaps to hold insulation? They look similar to the insulation hangers shown near the bottom of this page.
posted by Knappster at 11:30 PM on September 26, 2013 [6 favorites]

Condensation drip guides, maybe? To reduce the amount of time that condensation spends in contact with the concrete so it doesn't spall as readily?
I'm totally guessing.
posted by gingerest at 11:31 PM on September 26, 2013

No, for sure Knappster's got it.
posted by gingerest at 11:32 PM on September 26, 2013

Well, they're: A) regularly spaced; B) on a grid; C) not part of the original construction - unlike the drain supports, these are installed with adhesive (although the drain supports might be epoxied into the concrete).

I'd guess they were installed to allow them to suspend something lightweight (I'd guess a ceiling of some sort), in a manner similar to that of the nearby drain pipes, but they were either unable to do it or the element has since been removed. If the formwork for the concrete ceiling was 4x8 plywood, it looks like the spikes are about 3' on center, so a regular acoustic ceiling is out (generally based on a 2' module). So, I don't know what you want to suspend from the ceiling in a garage on a 3' grid.

I was thinking maybe an exhaust duct, which would be fairly common for an underground garage, but there's three rows, and you'd only need two to support a duct. For sprinkler pipes, you'd need something beefier.
posted by LionIndex at 11:33 PM on September 26, 2013 [1 favorite]

The ceilings of concrete structures are sometimes insulated with giant rolls of plastic covered fiberglass insulation. These batts of insulation are held in place with spikes that are glued to the ceiling.

From Knappster's link. That's certainly it.
posted by LionIndex at 11:35 PM on September 26, 2013

They're definitely insulation hangers. Seattle's building code requires insulation underneath the lower-most liveable floor level as of some recent date whose exact value escapes me. SPU has been giving incentives for building owners to insulate and I think the incentive program runs out at the end of the year.
posted by fireoyster at 1:14 AM on September 27, 2013

Hangers, yes, but not necessarily insulation hangers. Are they new, recently installed? If yes, then I'd say something else is going to be run along that ceiling. If they're old, then probably something was removed.

For instance: when a cellphone company paid to install new repeaters on top of my building a few years ago (why buy land and build a tower when you can stick them on top of an existing high-rise?!?), anyhow when they installed those repeaters they ran wiring lines all the way down the interior of the building and then out across the ceiling of the garage: the tubes containing those wires were hung from exactly that kind of 'spike', just like that exhaust duct? or whatever it is, only smaller in diameter & lighter weight. And again, when the building's security system was upgraded, more tubes were hung from the ceiling with more of those spikes.
posted by easily confused at 4:48 AM on September 27, 2013

Looks like drop ceiling hangers to me. Which would work with the insulation requirements - hang the ceiling (easy), throw insulation batts on top.
posted by notsnot at 6:34 AM on September 27, 2013

anyhow when they installed those repeaters they ran wiring lines all the way down the interior of the building and then out across the ceiling of the garage: the tubes containing those wires were hung from exactly that kind of 'spike', just like that exhaust duct? or whatever it is, only smaller in diameter & lighter weight. And again, when the building's security system was upgraded, more tubes were hung from the ceiling with more of those spikes.

I was thinking it might be something like that as well, but an installation of that kind of thing would only need two rows of hangers, while in the photo, there's a whole grid and you can see four evenly spaced rows parallel to the line of sight of the camera. It's possible that they could run a whole web of wiring down there, but a distributed system like that would not be really efficient to have with a concrete floor/ceiling - you'd have to drill holes all over the place to run your wiring. The fact that it's all in a grid here suggests that whatever was hung from the ceiling was an evenly distributed load that weighs very little.

Looks like drop ceiling hangers to me. Which would work with the insulation requirements - hang the ceiling (easy), throw insulation batts on top.

For it to actually be a drop ceiling, there would need to be something more substantial to resist seismic forces - you'll typically have metal stud struts every so often to prevent the ceiling structure from buckling upwards. The spikes wouldn't have the bearing capacity to do that.
posted by LionIndex at 8:02 AM on September 27, 2013

Response by poster: Yeah, they definitely look just like the things from Knappster's link. The building's already been inhabited for a year, so I'd be surprised if they were going to add insulation, but maybe that was the original plan and there's no real need to remove them.

Thanks!
posted by Cogito at 9:45 AM on September 27, 2013