In your special case, I wouldn't go so far as "ridiculous". If you account for some downward heat loss (into heated space), you could run with no insulation - and double bubble foil is a little better than that (mostly because of the bubbles). Or use Styrofoam.

radiant barriers are rarely very helpful in lower temp radiant applications, spray on or otherwise.

blueboard would be perfect except it offgasses. Did you rule out EPS foam already? You were speculating about it earlier, if that is ok for your sensitivities it would be a good choice for insulation.

timberframe homes often omit underfloor insulation on the 2nd floors. they have lower loads up there anyway, the downside is it lowers the output of the floor below and you have to make sure the zoning can respond on the lower floor appropriately. it's not ideal, but it might be ok.

Radiant barrier would be of marginal use at-best in a staple-up with the tubing & plates below the subfloor, and of even less use when the tubing is above the subfloor, with ~ R1 of subfloor between the tubing and space below.

What's wrong with rock wool (batts or blown)? It's inherently zero VOC. Unfaced R13 or R19 rock wool batts may be itchy while installing but don't leave fibers suspended in the air for long and they're about as non-toxic & inert a material as you'll find in the insulation biz. It doesn't outgas a thing even with a propane torch flame directly applied.

You might consider steel wall panels if the floor is too much trouble. I use them daily in my radiant heating designs.

You might also consider professional design, starting with a heat load analysis, radiant specification and insulation designed for the application.

Regarding the EPS - someone gave me something called "Barrier XT" which is basically EPS foam with foil on one side. It is very inert, and if this is something that might do the job, I'd consider it, but I don't know. Does anyone know?

With rock wool - I'd love a link to more information about that. For chemical sensitivities, by far the best insulation out there is AirKrete, but they don't have an installer in Colorado. I've also been looking into something called Eco Batt, by Knauf, but I don't like how they won't tell me what is in their resin. I'm waiting to test a sample.

It's hard to find any experts who understand both their area of specialty AND chemical sensitivities. You know how it is - if you're a hammer, everything is a nail. So I get wildly varying suggestions and just have to keep testing and hoping something will work both for me and for this system.

All this help is much appreciated.

I think that you need to find someone - anywhere - that has liability insurance and can give you "chemical sensitiviy" advice that is backed up by experience and insurance. You need to gut it up and spend a few thousand dollars and get some professional adivce, because mistakes here are very, very bad. Everything else can follow from that advice. Asking a bunch of us - people that have no experience with this and nothing to lose by offering you bad advice in this public, free-for-all forum - is just asking for trouble.

This is the wrong place to be asking this question because I think that you are asking the question in the wrong manner.

Jeff

Have to set the record straight  BARRIER XT  does not have foil on one side.  It is an under concrete/slab/crawlspace insulation.  It is EPS foam with state of the art polyethylene film lamitated to both sides of it.  We are a factory direct distributor of the product.

Chemical sensitivities are not rigorous Jeff: what some people are sensitive to others aren't, and there is a psychological component (if normal stuff starts bothering you, anxiety makes other stuff worse even if it is not physically reactive on its own, is the last theory I read). People suffering from this will never get solid definite clarity from any source without some trial and error, I think.

the AirKrete idea is a great one though, I will keep that in mind for future clients, thanks.

Believe me, if there were such a thing as a true "chemical sensitivities" expert, they would have all my money about now. Unfortunately, the experts in the field (Dr Martin Pall, Dr Grace Ziem) understand and can explain the scientific reasons why some people who suffered from toxic injury react to things, but they don't know building. And green building experts don't understand chemical sensitivity. The end all is that it's up to each sensitive person to both find out the best methods for building while also testing each product along the way.

In my situation, we have a mostly absentee contractor (he's literally in Disneyworld now for two weeks with his family while the crew is asking me to make decisions), and we've had such a horrible experience with our project that, honestly, we just need it done before we go broke. I'm simply doing my best to try to make it also work for me, as it would be nice to have a healthy place to live.

All that said - I have yet another question. The crew just called me to ask what kind of barrier I want to use under the 1 1/2 inches of concrete they are about to pour on the MAIN floor (over the plywood subfloor). What is the best building sciences material to use between the subfloor and the concrete so I can test that? I used Vaporlok under the slab in the basement, but that will be very buried whereas this is more in the living space since it's the main floor.

Thank you.

Also - I take it the Barrier XT (or anything similar with EPS foam and poly) can't be used under main floor radiant heat btwn joists then?

EPS can be used between joists. Dunno why you would want a poly layer though, with your issues you would probably just want plain EPS.

don't know about the thin pour isolation membrane, sorry.

The poly layer is for between the concrete and the wood subfloor as a few have suggested that is needed to prevent the wood (which is plain exterior grade plywood, not treated) from molding from all the moisture in the concrete. And also to help the concrete not crack I think?

Just a note about posting on this board -- I think it actually has been very helpful.  Green may not be always perfect for sensitive people, but it's a heck of a lot closer than conventional products would be.  At the very least, it's more cutting edge and people are more aware of options.

I'm curious - how do you determine if you are sensitive to something? Can you spend a day with it or rub it on your skin or something?

Honestly, it's not an accurate "science."  I do a sniff test first and if I don't react, I put it next to me for a while.  If I don't react, I sleep with it next to my head.  Sometimes I will heat it up in the car and then see how that is.  If I do react at some point, I still have to do the test again in case I was reacting to something else.  There's also muscle testing but I'm not great at that.

And even after all this, when it's a large amount in a home, it can be a problem even if a small amount tested ok, of course. 

I've learned a lot of what might work from other people who are sensitive.  Best book for this is "Prescriptions for a Healthy House" by Paula Baker Laporte.