Dry radiant floor in basement over Delta-FL?

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Baltic birch sleeper system is by far the best of all the "top" systems wood I have seen. It is an 11 layer, cabinet grade material. I suspect, if kept dry, it would be a very stable material.

I feel that thin aluminum material does very little to increase heat transfer. Way too thin! I consider the Subray to be a mini suspended tube application :)

Think I would look for a concrete anchor tool. Hitachi makes a pneumatic one that is less expensive than powder shots.

Most of the Climate Panel installers have a good method for this.

I like the insulation between, but it seems like a spongy layer?

hot rod

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Cliff Majersik

Dry radiant floor in basement over Delta-FL?

We’re converting our unfinished and un-heated basement into a playroom and bathroom. Right now its floor is just a bear un-insulated slab. The ceiling is already lower than we'd like so we don't want to raise the floor much. We’re thinking of using dry radiant floor heating under a floating laminate flooring -- i.e. without a plywood subfloor. The laminate would sit directly on aluminum conduction roll sitting on Watts PEX and birch sleepers (Watts Subray www.wattsradiant.com/lit/PDF/brochure/SubRayBrochure.pdf).

I’d like to put a thin air gap over the slab to reduce the risk of mold. I'm considering creating a 1/4" air gap using Delta-FL, which is a 5/16" thick dimpled polyethylene membrane that comes in 65'x5' rolls www.deltams.com/deltafl/index.html. (I think products like this have been used in Germany for 15 years.)

I’d also like to put a thin layer of insulation between the slab and the radiant pipes to improve response time. I'm thinking of using Solargaurd -- 1/4" of fiberglass sandwiched between two perforated layers of foil www.silvercote.com/reflective.asp. I'd lay the Delta-FL directly on the slab, lay Solargaurd on top of the Delta FL, lay the PEX/sleepers on top of the Solargaurd, roll out aluminum conduction roll and then lay the glueless floating laminate on the aluminum. The Solargaurd would compress to almost nothing under the sleepers and puff up to 1/4"-thick max between them. The Delta-FL would serve as a partial vapor barrier (only partial because we'd be drilling through it). We'll screw down the Subray head ends through the pre-screwed holes. I want to minimize the risk of screw heads working their way through the laminate. Has any one tried not screwing down their sleepers?

We're planning to use wet radiant under tile in the bathroom. We'll put the PEX in 3/4" of thinset on top of thin boards of rigid foam.

We'll use a Honeywell tempering valve to keep the water running through the PEX at 110F.

Our three kids (ages 1-5) will mostly use the basement playroom afternoons and weekends. So, we'll use a programmable stat to set back the temp at night to save energy. (We don't plan to put a separate stat in the bathroom.) We'll put area rugs over most of the laminate.

Background: 1910 row house in Washington DC with original hot-water radiators and a Munchkin 80k BTU gas-fired boiler controlled by a Vision One controller and outdoor temperature reset. We also have a 35-gal Superstore indirect water heater.

Does anyone have any tips, cautions or alternate suggestions?

Many thanks!

Mike T., Swampeast MO

You've definitely done your homework and your proposal seems to be made of good choices given the situation.

Only thing about the installation that bothers me is the floating floor installed over unsecured natural wood sleepers. Have never done or seen, but that certainly doesn't make it wrong. My concern is that the sleepers will twist, warp and otherwise move. Common modern lumber is nearly impossible to re-size without extreme movement. I've actually watched modern lumber curve when just attempting to straighten on a jointer!

As an alternate, I'd suggest an "unnatural" product. Perhaps composite "lumber" used for decks.

The only other flag I see is your thermostat strategy. Basements generally have little heat loss and the radiant floor doesn't need to be very warm to achieve comfort. Since this is a "play" room for children, they'll probably be reasonably active when using. You may well find it more comfortable and economical to keep a rather low but constant temperature. With that in mind, if you expect the bath will be used for regular showering/bathing, I'd suggest an intentional relative increase in it's heating ability. If mainly for toilet use but a shower/bath is available consider an IR heat lamp in the ceiling.

harvey

radiant ceiling

Why not a radiant ceiling? Hot rod had a post of this a few months ago. There are a number of ways to do it.

Unknown

in this situation (basement, uninsulated slab especially), you'd also want to carpet the floor though if you used ceiling.

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Unknown

2 birds - one stone

Cliff,

All the products you mention are wonderful. I prefer the Watts Sub Ray because of the 12 layer baltic birch. It is some tough stuff.

I believe that both SubRay and Clima Panel require another plywood layer below them prior to installation. I assume to insulate and secure to.

In your application why not use the Roth Radiant Flooring System. It has an R-3 built in and will only raise your floor 3/4". Glue the Roth panels down and float your floor on top.

www.roth-usa.com

Larry_10

Thanks to all! Thinset vs. cement board subfloor?

Thanks to all for the feedback and tips!

I don't think the Solargaurd insulation will cause sponginess because it will compress to just a millimeter or two under the weight of the Subray. You can easily compress it between your fingers.

Does anyone have an opinion about the best and thinnest subfloor under tile for our basement bathroom?

Option 1) Delta-FL, Solargaurd, Subray/PEX, Durock cement board, tile.
Will a 1/2" or 5/8"-thick Durock board without a plywood subfloor be rigid enough to prevent tile cracking?

Option 2) PEX in thinset concrete under tile.
How thin can we pour the thinset without causing tile cracking?

Should we reinforce the thinset with something like chicken wire?

Is there a 1/4"-thick insulation (maybe a very rigid foam) that we could put under the PEX in thinset that won't compress and cause tile cracking?

Thanks again!

Cliff