We're in the process of having a healthy home built (low or no VOC products as we have severe chemical sensitivities).  

The house is AAC (autoclaved aerated concrete) walls. 

Questions about radiant:

- The walk out basement has a 4 inch concrete slab and the radiant tubing will go in there (contractor recommends tying to steel grid). 

- With the main floor, though, we're going to have radiant.  The flooring will be EcoTimber engineered hardwood over (this is what we're trying to decide) either
gypcrete
lightweight concrete (1.5 inches)
staple up

I'm worried that gypcrete has stuff in it that will be problematic for chemical sensitivities. 
With either crete system, I was told that we will need vapor barriers over the plywood subfloor, and am unsure what barriers would be the best for VOCs and also to protect against trapping moisture (mold is another sensitivity).

Staple up won't have the thermal mass we're going for, although reading online, I see that the gypcrete and lightweight concrete might not actually have as much as I thought.

I was also told that we'll need to have insulation in the floor to prevent the heat from going down.  Makes sense, but we picked AAC block walls to avoid insulation (again due to sensitivities).  I don't do well with the spray foams (e.g. Icynene, etc), and was going to use the Johns Manville Formaldehyde Free in the attic insulation, but with a vapor barrier to block the fumes from entering the living space.  Now we're wondering how to insulate the floor in the least VOC manner possible.  Considering sheep wool, but it's expensive.  Considering the jeans, but wonder where they've been! (e.g. fragrance/mold toxins, whatever else on old, used jeans).

On the concrete subject, we're looking to stain the basement floor and are seeking suggestions for no voc low maintenance concrete stain.

Thanks for any advice
Jill

are blown cellulose insulation products a problem (basically newspaper)? Soy foams?

you only need thermal mass if you are designing for passive solar gain. That said gyp or concrete will probably outperform any staple up. without knowing your heat loads it's hard to say if that's a problem though, it might not be.

mold between the floors shouldn't be a problem if you are heating the basement and the 1st floor. it's the transition from heated to non-heated space that typically has moisture/mold issues. you would only need an isolation membrane under 'crete (not a vapor barrier) between heated floors. the staple up option wouldn't need that.

There are many other methods: warmboard, and various other over-the-subfloor panels, but I don't know what their various VOC profiles are. Most are made out of some kind of plywood or MDF.

Why not go with regular concrete. Our floor is regular concrete (1.5") on a plywood sub floor. We just beefed up the joists for the load. The extra thermal mass is nice for the fall and spring when temps swing more. It buffers the temps. changes.

actually, mass *envelopes* buffer temp changes. mass *heat emitters* cause temp swings when the emitter cannot change output to meet a changing load profile.

Unless you're lucky, or controlled well, of course.

Actually, the floor is a mass "buffer" in the fall and spring because it is not an emitter at that time. With proper envelope insulation the heat does not come on at this time of year and the floor buffers the temp swings.

only if it's designed for passive solar absorption and you aren't running the heat at all. Sounds like you might be there... awesome!... but most people can't say that.

Not too many homes can say their heat doesn't come on in the fall and spring, and for most homes, mass emitters make those "shoulder seasons" problematic because you have to charge up a big mass to get just a little heat.

solvable, but not always simply. especially not in very tight homes where the heat charge in an emitter can cause a swing quickly.

Over-the-subfloor systems such as WarmBoard (tm) etc. are fast-responding & low-temp- (lower temp than staple up, anyway) and work fine with engineered hardwood flooring.  They have the added benefit of avoiding the rock-hard zero-flex of concrete/gypcrete solutions.

For the sub-floor insulation, if you can tolerate newspaper ink cellulose has no other outgassing potential and it's inorganic borate fire retardents (usually boric acid) are also mold-inhibitors.  TDry blown cellulose may contain aluminum sulfate fire retardent, which corrodes metals when wet, and is more likely to be an issue for hyper-senstive people than boric acid.  Specify "sulfate free" or "borate only" material and you'll be fine (there are several manufacturers out there.) Cellulose also has some thermal mass- far more than most other insulation materials.  R20 of medium density cellulose has about the same thermal mass as a half-inch of gypsum on a per-square foot basis- enough to make a measurable difference (but nothing like an all-concrete house.)

If cellulose won't work for you, blown rock wool is completely inert, with ZERO outgassing potential.  It's spun slag, a byproduct of steel-making.  Any outgassing it was ever going to do happened at high temperature back in the steel mill.

Sheep wool has all sorts of outgassing issues, as does cotton (if you get a reaction to either you'd probably have noticed by now though), and both would need fire retardents added for use as insulation- read the specs carefully. (Most cotton insulation uses the same borates that are used with cellulose insulation.)

What you're looking for to isolate potential outgassers are not vapor barriers, but AIR-barriers.  Volatile organic molecules are typically several times the size of diatomic nitrogen or diatomic oxygen- anything that blocks air will block them, for the most part.  But water vapor is half the size of N₂ & O₂, and will diffuse through many materials that other components of air do not. Randomly inserting true VAPOR retarders in assembly is a recipe for disaster, but air-barriers can (and should) be applied liberally.  If you can tolerate polyolefin, many housewraps can be impressed into duty as air-barriers in other types of assemblies than just exterior walls, without creating moisture traps.  You may still need vapor barriers/vapor retarders in other assemblies, depending on climate & construction.  The most common true vapor barrier material is polyethylene, but if that's a problem for you there are metal foils & aluminized polyester sheeting (the polyester is completely encapsulated in the aluminum) sold as "radiant barrier" that can serve the high-vapor-retardency function.

You need to be careful with any "over subfloor' panel system. they are all some sort of plywood or the like and would need to have their offgassing potential verified before use. I believe you can buy no-VOC plywood these days but it's unlikely any prefab panel is likely to use it. Joist, 'crete, or perhaps site built panels from "clean" plywood products would be the best likely solutions I can see.

I would do some research on filtration systems (like activated carbon) and on using ozone just after construction to knock down voc levels.

I opened my windows for off-gassing and a heat recovery ventilator is a must in any new energy code compliant home.

You may consider steel panel radiators if sandwich systems and insulation are impractical. There is also RauPanel to consider.

High mass floors are of little use in a well insulated home as Rob points out. Sprayed cellulose is GREEN and toxin free and Dana says.

Soy foams have similar components to other spray foams (e.g. Icynene, Demilic) and those don't offgas enough for me.

Haven't actually tested newspaper because was concerned about petrochemicals (ink) and mold issues.

I was researching and found things like Radiant Barrier and similar products.  Has anyone used these successfully? It's supposed to be both a barrier and insulator.

Yes, I'd love Warmboard but it has too much crap in it (like OSB does) for my sensitivities. 

Thank you - good point on the air/vapor barrier distinction.   Are you suggesting that the barrier between the plywood subfloor and the lightweight concrete/gypcrete needs to be an air barrier, not vapor barrier? For the attic insulation barrier I mentioned, we were going to use Tu Tuff (polyethylene).  But I've been questioning whether we want to do any barrier there at all.  What is your opinion? There seems to be just as many people who say it's best to isolate the attic space from the living space as those who say "don't put a barrier there because of potentially trapping moisture."

I will look up the blown rock wool.  Haven't seen that locally...(Colorado).  I don't think I felt great around the denim insulation, but can't tell why yet.

I wish there were a no-voc warmboard.

Question for all -- what about sandwich radiant system (just read about that online) - lots of labor, but is it worth it? Still less than concrete?

1. For free: Research House for the Environmentally Hypersensitive, Canada Mortgage and Housing Corp.
   <http://www.cmhc-schl.gc.ca/en/inpr/bude/heho/upload/Research-House-for-the-Environmentally-Hypersensitive.pdf>
2. For free: The Medical Perspective on Environmental Sensitivities, Canada Human Rights Commission, M.E. Sears, M.Eng., Ph.D.
   <http://www.chrc-ccdp.ca/pdf/envsensitivity_en.pdf>
   
3. For fee handbook ($30) : Building Materials for the Environmentally Hypersensitive, Canada Mortgage and Housing Corp.
   <https://www03.cmhc-schl.gc.ca/catalog/productDetail.cfm?lang=en&cat=8&itm=25&sid=946d2787b50b4d0f832313c812c5cb83&fr=1284087844138>
4. For fee handbook ($20):  “Optimum Environments for Optimum Health & Creativity, Designing and Building a Healthy Home or Office", William J, Rea, M.D.
   <http://www.ehcd.com/books/home_building_designing.html>

All are excellent resources.
rb

Site built panels are what I'm looking at now.  We've been using exterior grade plywood which seems to offgas a lot less.  No, you're right, I absolutely couldn't tolerate something prefab like Warmboard.  Originally I was thinking staple up under the subfloor as the other option, but now I'm thinking of site built panel idea...

Please excuse my lack of proper terminology.  Learning as we go...contractor great but not familiar with radiant and radiant co, of course, just wants to pour Thermafloor.

Raupanel looks interesting, thank you.  Any idea on how it compares in terms of price?  Also need to ask them what materials contain (e.g. glues/formaldehyde). 

Insulation is such a tough one for people with MCS - hard to tolerate most of them.  Hard to do a real test that would mimic an entire house full of the product...a big decision...

Wow - thank you! 

Sorry for all the repetition and wows - thought I was replying individually.  Appreciate the opinions and open to more.  Appreciate the links to EI resources as well...

We've been following a great book called "Building a Healthy House" by Paula Baker Laporte...but not much about these issues/radiant in it.

Greetings all,
I have been following this thread for a while now, lots of good information.
A sandwich system is a good choice, offers low delevery water temp, fuel efficient.These are easly done by your site carpenter and plumber. We offer what I think is one of the least costly site built type system.
RHT Floor panel system. There are of course others out there. our system uses locally purchased 3/4 ply, we provide the pipe, turns and heat plates.
Good luck with your project,
Dan

we use site built panels regularly. they are good. Raupanel has better output, but it's more than twice the cost and we've seen some noise concerns with it.

There must be a no-VOC sheet good product out there. You don't have to use plywood, we usually do, but you could do "sleepers" of 1x or 2x material as well if that helps. Might be a little pricier but maybe easier to find "clean" products to use that way. just has to give you the height you need, hold a staple, and support your finish floor.

Radiant Barriers can help insulate but ARE NOT SUITABLE INSULATION BY THEMSELVES. they also require an airspace.

There was another interesting application done with our 12"x24"heat plates, 1x4 flat 12oc plates attached, pipe snaps in plate, finish floor nails to 1x4 12' pattern. no ply wood, pipe is on an 8 inch pattern and snaps in to plates, low temp system 100 degrees. hold the pipe on turns in place with several wide low profile romex electrical staples
Dan