How to best insulate a concrete ceiling in an old warehouse

Question

We're renovating a three-story, 100-year-old brick warehouse with 14" thick concrete floors/ceilings that are heavily reinforced with rebar. The building is COLD and we would like to insulate the ceilings, but aren't sure what would work best.

We plan to cover whatever insulation we use with sheets of corrugated metal, to keep with the old warehouse look. We're worried about condensation, since we've heard that can be an issue with brick/concrete. We would greatly appreciate any suggestions (especially what NOT to use).

Answer 1

Condensation is an issue for any cold surface in contact with warm, moist air. The typical strategy is a vapor barrier to prevent the moist air from reaching the cold surface on the other side of insulation. Foam board insulation panels with taped joints provide a vapor barrier. Alternatively for air permeable insulation you would use plastic sheeting or an outer layer of foam board insulation with taped joints.

Corrugated weathering steel is designed to rust, where you might like its aesthetics for your old warehouse motif. Inside it might never rust, though, without some encouragement from something like a vinegar/bleach solution.

Answer 2

In my youth I did some work to help insulate an office building. The ground floor was a drive-in carpark, with offices above that.

We "drywalled" the ceiling by fitted large panels of polystychrene about 60mm thick. They were secured under the concrete with plastic "nails" that had large heads to spread the load.

The hardest part was drilling upward into concrete overhead, followed by sealing every gap with a manual cartridge gun. I don't recall the product used.

This was a carpark so looks weren't important. The white material did make it noticeably brighter, but over time car exhaust darkened it all. Sadly there are no photos.

In your case, another option is a drop-ceiling with fibreglass batts on top.

You'll also need to insulate the floor above too, with some kind of thermal barrier. This could be a good time to spread that space-blanket thermal reflector out of sight too.

Sadly most "concrete factories" are not made for sedendary activities. Workers would have been moving and keeping warm that way. You have a big task ahead of you, good luck !