Insul-tarp or equivalent

wchevron

I have a church we are installing radiant heat in. Basement below is heated with baseboard. Basement ceiling is finished. The contractor pulled up the tile floor in the church. Plywood is underneath. They are laying another layer of 3/4" plywood down then want to only pour a 2" concrete slab.
We have always used 2" blue foam under any slab, or if it was a 1st floor like this one, insulate the joist bays beneath, but we don't have access to them in this scenario. The architect suggested Insul tarp but I don't have any experience with it. Did a search on here and it doesn't seem to be recommended. Can anyone recommend another product. Need something thin. What about bubble insulation?

RobG

I would just stick with baseboard or do panel rads. I wouldn't put my reputation on the line if it doesn't work. Those products are both junk.

Tinman

Something is better than nothing but there's a lot of smoke and mirrors associated with many of the thinner insulating products used for radiant.

If you are limited in terms of height, you may have no choice but to use one of the thinner products. Just know going in that the marketing for these products may be outdoing the actual performance.

Tinman

What about suggesting drilling and blowing insulation in the basement ceiling? Easy to patch.

Gordy

Fanfold insulation is better than that stuff, and it' is r 1...... Which is 100% better than R 0.

Not that I would use it for your application.

I hope the architect verified the loading for the 2" concrete over pour.

Tinman

1" of solid wood has an R-value of 1. If that's all you want, put another piece of plywood down. 1" of blown insulation has an R value of 3.21. Do the math based on the height of the ceiling joists.

Gordy

I like the blown in insulation Steve suggested.

hot_rod

concrete slab over a wood framed floor? Better have a structural engineer look that over, that should be your biggest concern.

SWEI

Do they actually have to have concrete, or was it just the simplest looking thing to do?

wchevron

I think the architect had his structural guy look at it. Not exactly sure on the concrete decision. I think they are either going with an architectural concrete finish or tile. I'm too low on the totem pole to know the answers.

hot_rod

Maybe let them know that a 2" thick slab will hairline crack like crazy, possibly over every tube. It may not be a wise investment to try and finish, color or stamp a thin slab like that. It will require a cleavage membrane if they want to tile over it.

Also, unless the framing is really beefy you will get some bounce which adds to potential cracking, which could transmission thru to a tile adhered to it.

For thin slabs you need to mix with a pea gravel aggregate, as you need 1-1/2 time the aggregate size over the tube to get a good consolidation.

years ago we tried to blend some lightweight concrete mixes with Perlite, that didn't work out so well. it still cracked and had terrible heat transfer

IF they really want a slab over framing consider one of the high PSI gyp blends. Some of them can be used as final wear surface now. They self level, flow around the tube better and don't craze and crack like a concrete mix. Still about the same weight per square foot for loading, however.

Tinman

Therma-Floor gyp by Maxxon? That's what I use.

Gordy

You can do some very creative finishes for concrete. If you want to spend the dollars. As HR says if that floor does not meet the live loading with out bounce could get ugly. Deflecto calc for tile. If tile that adds more weight still.

There is quite a difference from architect to designer to engineer in thought process.

kcopp

Why not just do a dry system like warmboard or Quik trak?

Zman

I understand that the OP had a specific question and this is a bit off script.
Why woulds you install a high mass radiant panel system in a church? Everything will work great until 200 church goers show up at 600 Btu's a piece. The room will overheat. How is the building ventilated? I hope they are not considering setbacks, although high mass aside, this might be a good application for setbacks as they only use it a few days a week.
Low mass, floor panels like Kcopp suggested or low profile radiators would be great.

If they insist on proceeding with the plan, you could blow in insulation by drilling holes in the floor that will be covered by the next layer of plywood. Insultarp is a hoax!

Tinman

What kcopp and Zman said and maybe consider Roth panels. Kill 2 birds with one stone.

Gordy

Understanding what's available in the realm of radiant floors, and how it fits into a design requirement parameter is key here. Does the architect understand options, and has Zman pointed out design requirement for the application.