Ideas for installing a thermal break joint in an existing concrete slab???

[jm0309]

Hi everyone,

New member and first post here. We have a Client who has a freezer room next to an office (separated by an interior partition wall) and they are experiencing condensation on the interior wall and along floor between the two rooms because of the temperature and relative humidity differential between the two spaces. I was informed that this phenomenon is known as "thermal bridging".

One of the solutions that our building engineer is recommending is to provide a joint in the concrete floor slab filled with insulation foam (directly underneath the interior partition wall that separates the two spaces) in order to provide a thermal break between the two spaces. Right now, it appears that one of the contributors to the condensation on the wall and floor is the travel of the cool air from the freezer room to the warm side of the office via the concrete floor slab. The concrete slab construction is currently unknown. It is possibly between 6 to 12 inches thick. It is either reinforced concrete slab on grade or a post-tension concrete slab.

My question to everyone is - what are your ideas on how to go about installing this new insulated joint in the concrete slab to provide a thermal break? Presumably the slab will need to be cut through its entire thickness in order for the thermal break to be effective. I have concerns about cutting through the rebar if it is a concrete slab on grade and I have even bigger concerns about cutting through the post-tension cables if it is a PT concrete slab.

Any ideas would be appreciated!

 

[KootK]

This is a slab on grade for sure though, right? Cutting the joint into a mildly reinforced slab on grade is probably not a big deal. As you've anticipated, it might be a pretty big deal for a post-tensioned slab on grade. If it makes sense for economics and headroom, you could place a topping slab and insulation over top of the existing slab on grade to get it done?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jm0309]

@KootK, we are not sure if it is a slab on grade at this point, so I am sure some concrete investigation will be required in the future before we do this work. We are having a meeting tomorrow to discuss our options (I was just informed of this project this afternoon, lol). We were already informed by the Client that building up the existing slab (like via a topping slab per your suggestion) is not preferred.

My concern about cutting a concrete slab on grade is that the joint may have to be cut all the way through the slab thickness for the thermal break to be effective, as opposed to just cutting a shallow sawcut joint and filling with insulation material.

 

[KootK]

Surely you know if this is a suspended slab or not? We must be suffering from terminology differences or something. Does the slab sit on top of the ground or is it suspended in the air on columns and/or beams?

For a ground supported, mildly reinforced slab, the full depth cut probably won't pose a problem unless you're dealing with serious racking loads etc.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jm0309]

hi @KootK, sorry for the confusion. No, this is not a suspended slab. It is on the ground floor of the building. I am not sure if it is mildly reinforced or if it is post-tension. The Client is trying to find some record drawings to find out. Otherwise, we may do some GPR scanning to determine the reinforcing. If we are making a full depth cut of the slab (let's assume it's mildly reinforced), would it be an issue to cut through all the rebar? I would imagine that we need to install some dowels in order to keep the slab acting as one continuous slab? Like I said, one room is a freezer room, and the other room is an office, so I assume the floor slab loading is quite different, even if they are not racking loads.

My apologies for the jumbled (or lack thereof) information. I only learned of this issue today and am trying to get some brainstorming going before my meeting tomorrow.

 

[KootK]

No sweat. Yeah, if it's just mildly reinforced slab on grade, I'd think that the worst case might be that you have to cut back the slab a bit to install thickenings either side of the joint. And even that may not be necessary.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Compositepro]

Another option is to glue a low powered heater strip to the floor right next to the refrigerator. Most commercial refrigerators have strip heaters around the doors (on the insulated side) to prevent condensation. The sheet metal around the door is a relatively good conductor of heat. Adding insulation will only move the location where the metal drops below dew point and sweats.
Ventilating the wet area can also be a solution. Ventilation can heat the area enough to not sweat.

 

[Once20036]

The only other caution that I'd add is that if this is a PEMB, a full depth cut through the slab on grade could compromise tie reinforcing between columns.
Like others have said, if it's not a PEMB or PT, I'd cut it.

 

[dik]

If there is the possiblilty it is post-tensioned, you might start with a low energy chipping hammer to expose whatever reinforcing. If normal rebar, then out with the saw...

If putting the joint in the concrete, you might want to align the joint with the outside edge of the partition (cold side). Some (any permanent freezing cold storage has heating loops under the slab to prevent frost from going down into the soil. Careful for the heating loops.

Dik