Hello, I am remodeling a 1930s adobe and considering flooring/heating/insulating options. Already determined is that there will be in-floor radiant with brick as finish floor. What I can't decide is whether the tubing should be in a new slab poured throughout the house (right now the "floor" is just dirt), or whether I can put the tubing in sand and have brick as finished floor. I think it would be nice to avoid filling the house with concrete and it would save on labor in terms of how much I have to dig down inside the house to get the right grade; however there are areas where I worry about settlement/compaction issues over time, for instance under the bathtub, and in high traffic areas or areas with heavy furniture on top. I will compact beforehand, but face certain challenges. I can't use a gas-powered compactor inside, and I need to be sparing with how I apply water to the ground, given that the house is made of adobe and the footing of rubble with mud mortar. In either scenario I am trying to figure out how to insulate. This is climate zone 5. The building is all adobe with no insulation in the walls, and the footing is rubble, likewise uninsulated One thought I had was to first insulate the footing on the inside by going down 24-in with 2-in rigid. Then I was thinking of installing radiant pex panels throughout the house, like the Amvic product sold at home depot. In most areas I would add a sand bed to fill the grooves and cover the radiant, and lay brick on top of that. In areas that might be supporting heavy loads, like bathroom (where I also want to tile), I could pour concrete on top of the panels and then put down the finish floor. I was hoping another benefit of this would be increasing the response time of the system, as the climate in my area can fluctuate rapidly from day to day during certain seasons. Any thoughts? Do I still need to worry about an uneven floor, with the panels bowing or cracking under the weight above wherever there are inconsistencies in the ground itself? And do I need to buy that insulation product or could I improvise a similar situation?

Sand is fairly insulating (about R0.6 per inch) and not the best place to put the tubing. Embedding the tubing in a slab and using a thin brick flooring on a 4" slab can work.

Going down 2' with 2" EPS wouldn't quite cut it for zone 5. Ideally you'd want at least R10 slab-edge insulation down to 2' below grade even with slabs that aren't being used as the heating radiation. At 2" XPS is labeled R10, but as it's climate damaging HFC blowing agents diffuse out over a few decades it's performance drops to R8.4. At a minimum use 3" of Type-II (1.5lbs per cubic foot nominal density) EPS at both the slab edge and under the slab, which would be R12.6 now, and still R12.6 fifty years from now. It's probably going to cost rational to go with 4".

If there is a building materials reclaimer near you trading in used foam, Type VIII EPS (1.25lbs nominal density) is fine. At 3" it's still about R12.4 or more. Any used XPS should be derated to it's fully depleted R4.2/inch (about the same as Type-II EPS.) Reclaimed EPS is usually less than 1/3 the cost of virgin stock foam and WAY cheaper than Amvik panels. Most reclaimers have polyisocyanurate roofing foam in stock, which should NOT be used under slabs, since unlike XPS or EPS, it can become waterlogged and lose performance over time in wetter soil conditions.

Amvik's AMPEX 2015F is also Type-II EPS molded for ease of routing the tubing but that's not necessarily what you want for a DIY. It's considerably more expensive than straight-ahead plain sheet goods, which may have some pay-back if you're paying a contractor, but most will come in cheaper using XPS with the tubing stapled to the foam with plastic staples. Type-II or lighter EPS has lousy staple retention, but 3" of Type VIII EPS overlaid with an inch of XPS can be a good compromise.

When pouring a slab over foam it's good practice to put a sheet of 6 mil or heavier polyethylene on top of the foam. That avoids any pockets of liquid water from developing under the foam or in the seams between sheets that will take forever to dry, and can affect the finish floor. None of this may matter too much in well drained sandy soil in the desert southwest and using brick as a finish floor, but the a ground vapor retarder to limit soil gases (radon, anyone?) from entering the house is also important.

BTW: got a ZIP code?

Thanks for the detailed response. Zip code is 87501.

A few followup questions:

Overall, is the insulation suggestion to put 3" EPS + 1" XPS beneath the entire slab, and 3"EPS around perimeter going down 2' below grade?

A contractor will be installing a radon gas mat collection system around the perimeter of the house. My understanding is that there will be a 6 mil vapor barrier on top of the entire floor, then the insulation. Therefore I would want to skip the second vapor barrier if possible, but then would the concrete be poured directly on top of the foam? Or would it need an inch of sand or something to help with the moisture and curing?

Finally, Are there any ways to install radiant tubing beneath brick that would not involve concrete?

Thanks again!

Thanks for the detailed response. Zip code is 87501.

A few followup questions:

Overall, is the insulation suggestion to put 3" EPS + 1" XPS beneath the entire slab, and 3"EPS around perimeter going down 2' below grade?

A contractor will be installing a radon gas mat collection system around the perimeter of the house. My understanding is that there will be a 6 mil vapor barrier on top of the entire floor, then the insulation. Therefore I would want to skip the second vapor barrier if possible, but then would the concrete be poured directly on top of the foam? Or would it need an inch of sand or something to help with the moisture and curing?

Finally, Are there any ways to install radiant tubing beneath brick that would not involve concrete?

Thanks again!

Without the structural rigidity of the slab to support it a brick floor is going to move around a bit, and the foam insulation is going to develop compressions at the seams between sheets. Even a 2" rat slab does quite a bit for reducing that risk but the slab is pretty much guaranteed to crack if it's that thin, even with wire-mesh reinforcement. Cracks may not matter much if with hard brick bonded to it with thinset as the finish floor, but it would be a problem for tile.

Concrete can be poured directly on top of foam. The only real issue is moisture trapped under the foam. With brick or tile as a finish floor that's not really a big deal, but the slow drying of that moisture can mess with polished concrete floor finishes or engineered wood, carpeting, etc.. A layer of sand does nothing for containing/managing moisture during the pour, or at any point after.

BTW: The foam reclaimer Insulation Depot has a warehouse in Phoenix. They're currently advertising truckloads of polyiso (which you DON'T want to use) located in their Phoenix facility in the Albuquerque craigslist ( https://albuquerque.craigslist.org/mad/d/iso-rigid-foam-insulation/6547116555.html ), but they almost always have EPS as well. I believe they have a warehouse in Colorado too where the shipping might still be reasonable. (You really DON'T want to pay shipping from their Massachusetts warehouse. :-) )

When you figure out how much foam you're going to use it's worth getting a quote that includes shipping. Even with shipping it should be less than half the cost of virgin stock goods from a local building materials distributor. Be sure to buy 10-15% more than you need to cover any mangled sheets that turn out to not be usable. (They claim at least 90% will be usable, but pad that a bit. Read the conditions: http://www.insulationdepot.com/terms-conditions.cfm ) Either EPS or XPS is fine for your application, polyiso is not.

http://www.insulationdepot.com/

Great info, thanks so much Dana!

Have you talked to people who work with adobe? I'd want a second and third opinion before I started to dig around a rubble foundation. This guy should have some answers. http://www.quentinwilson.com If you want brick because you like the look, consider thin brick applied with thin set over a radiant concrete slab. https://brickit.com Again, you need local expertise to tell you how thick the slab should be. Or thin. Your house, built with little more than trowels and buckets, is mostly through its ninth decade.

Good point about not messing too much with the foundation! This isn't a concrete stemwall on a reinforced concrete foundation.

You might need to give the heated insulated slab a bit of clearance from the walls to allow room for thermal expansion/contraction, and not dig down to install deep slab edge insulation that might disturb the foundation.

Good thoughts, and good references, thanks!