Cellar Build Question

Looking to ping the minds of those much smarter than I at this…

I’m building a cellar (11x7) in my basement, when the home was built I had them put closed cell foam in the walls and ceiling. The basement is a walk-out, but the area the room is in is completely underground (10ft ceiling, so floor is probably 12-14ft underground). It will be actively cooled via a Cellarpro unit and the basement has HVAC.

I have pretty much everything worked out except what to do with the floor. My current plan is:

Spray concrete sealer to seal the floor:
https://www.amazon.com/Lithi-Tek-9500-Ultra-Concentrate-Waterproofer/dp/B00H6QR8D8

Subfloor with DRIcore+ (R value=3):

Then cork pre-man flooring on top

I figure with the DRIcore, any condensation will be able to contribute to the humidity in the room while keeping the floor dry, and given I’m decently below grade (in NC) I shouldn’t have a huge temp gradient to deposit a lot of moisture. There is also a sump-pump 5 feet into the next room to keep things dry.

What are your thoughts? Is this enough, or should I lay vapor barrier under the DRIcore?

Anyone have an opinion?

I am not smart enough to know which of your two options is best.

We have a cooled below grade cellar and used concrete sealer/stain, so have just the concrete for the floor and none of the stuff on top that you mention.

All my cellars have had simple concrete floors below ground. No problem. The only downside is looks. Painted one with epoxy which looked great.

Less insulation on the floor is better. It’s a heat sink that far below grade.

Love in MA with similar cellar in my basement. Just throw tile down over the concrete.

I am not an expert but FWIW was advised by one not to use cork (gets messy if mold gets under around I was told) - I used tile set in grout.

Awesome, thanks for the input!

feet or yards?

My cellar is completely underground … and it is concrete without anything on it …
works fine, humidity is 75-80 % - temp. (passive) is 12-13°c (53-55°F) in summer and 8° (46°F) in winter …
no need for anything else …

If you insulate the floor you probably will need more air condition - I suppose …

Why do anything to the floor? I had a concrete floor for many years, no problems. Similar situation to yours. It’s a closet after all.

If your floor is the temperature of bedrock, then you shouldn’t insulate it. If warmer, then you should.

What is your floor temp? If its 55ish, i see no reason to insulate the floor. I wouldnt even seal it. It will help keep the cellar humidity higher in winter, but you will need a good plan for draining excess condensation in summer.

If the floor temp is above 55°F you definitely need to insulate it. When I built my cellar in Atlanta I figured the heat load from the floor would be huge without insulation. Concrete has an R value of 0.5 so heat will flow thru it without resistance. I put down 2" thick pink styrofoam closed cell foam boards from Home Depot with stained 1/2" plywood on top.

Somehow you need to find out what that floor temp will be towards the end of summer when earth temp has risen to its highest point. If you are up in the mountains you may be OK but if not you might be better safe than sorry.

My initial response assumed you were in MI based on your avatar. Ground temp 12’ below grade there is well below 55 degrees. However, in NC that number is likely between 55 and 65 degrees. As others have said, if ground temp < cellar temp, don’t insulate the floor. If ground temp > cellar temp, insulate the floor.

Yea, I think I need to insulate, I’m in Charlotte. Looking at the ground temp charts floating around out there and nothing looks promising for me to be under 55 in mid-late summer.

It’s not a heat sink in NC - average deep ground temperatures there is in the 57-62 degree range (warmer towards coast), and that will fluctuate seasonally at 10 feet down by +/- 5 degrees. Plus, you have open space above it, not 10 feet of soil, so the slab temperature will tend towards the basement temperature.

In other words, insulation on the floor is a good idea.

Search for some of my posts on my cellar build - I did close to the same thing you’re planning - I used a dricore like product and it seems to work well. The idea is sound - it gives some room for a touch of airflow if there’s moisture (those channels between the squares) while creating insulation above. That helps with any condensation that could occur (both through insulation from above and with airflow). I also used manufactured cork flooring. It’s finished on top, so not worried about mold (and it hasn’t been a problem with humidity from 50-70%), and the softness is nice underfoot and may help reduce accidental breakage, esp. vs. cement. If you haven’t gotten a sample of the flooring, order one and see!

ETA: Sorry, David - didn’t see your followup before posting this (wasn’t picking on you, I swear!):

You guys rock, I knew I could count on ya’ll for some great info. Hopefully getting started in the next few weeks. I’ll be sure to post pics.

Hi Andrew

Sorry to weigh in late but I think the dri-core product you mentioned might be a problem since it has an osb backing. This backing could potentially fail in a humid/damp environment. Tile as some others suggested should work or if you want something “softer” vinyl laminate (the kind without particle board backing) should work and not be susceptible to water damage. I have used it in my beach condo with good results. Probably has very low insulation value however. I am sure there is some sort of insulation board that is not susceptible to water damage that you could lay underneath if you decide to insulate.

Andrew what have you decided on your door? For those with a cellar would you recommend with or without glass for the door? Do I need some sort of UV protection for the glass for possible diffused sunlight?