I'm building the Global Earthship design in a high radon risk and very cold climate part of CO. See the drawings at www.gunnisonearthship.com. I'd like to go ahead and mitigate any chance of high radon counts by installing a 4" sub-slab depressurized gravel/perf pipe to a manifold up our warmest wall through the roof. Since our home is only heated by passive solar on our 6" adobe floors, I'm worried that the depressurization may conduct/wick the heat out of our slab mass and out the roof vent. Does anyone know if this is a significant convection heat loss in this kind of radon mitigation design? Our 6 ft. thick rammed walls have a thermal/vapor wrap of 4" of rigid insulation/12mm poly, but our floors do not. I'm wondering if the solar charge of our slab floors would not create the heat sink necessary for a stable radiance during cloudy days if it had a thermal break of insulation to protect it form the radon depressurization. Our living space slabs have a 13' greenhouse zone separating it from the outside soil/frost lines to the south, 25' of garage zone buffering to the west and 20+ of rammed earth and berm buffering to the north and east. I'll have 2" rigid on both the greenhouse tire wall and structural wall footings. I may want to scrap a sub-slab mitigation with all of the chances that it may not create enough depressurization and, instead, mount low-watt heat recovery ventilators on my ventilation tubes for each bedroom. Anyone have experience with mitigating radon with HRV's? What cfm is needed per room sf? I'm planning to start this phase in June. Thanks, Eric

Your going to be better off radon wise if you install a floor vapor barrier. How many CFM are needed (for the room or underslab) depends completely on the specifics of your building/site.

Once you know the CFM, you can calculate the heat loss - or use an HRV on the underslab air.

Hi, Eric. I asked a similar question a few months ago and got some good replies, concluding that it should be fine so I'm going ahead with it. You can read the thread at http://www.greenbuildingtalk.com/Fo...aspx#57486 .

I love the Crocus design of your house. I've had to ungreen some planned features of my house because the costs were getting too high, so I'm very jealous of you!

Good luck,
...Terry

I'm not sure if you covered this. Why don't you insulate the slab? If you poured the slab on foam board it would insulate it and you could put your radon mitigation under the foam.

In 2009 we had a passive solor slab home built near Divide Colorado, the solor slab was a waste of money. Inovative Structures, Matt Freidell built the home and fan he put in is noisy and annoying. We built in a high radon area and he did not advise us of this. The slab is poured on concrete blocks, which were poorly sealed from radon. The space below the slab acts as negitive air space and sucks the radon to levels of more than 40. I had to seal all ventilation from the slab, and draw the air from the slab to the outside to get the radon levels under 4. For us it was a waste of money, this is possibly due to an incompetant contractor, Inovative Structures.

Do not use Inovative Structures, Matt Freidell, he did a poor job sealing with a vapor barrier and the space in the slab area created a negitive air space which sucked radon from the ground in our home. We had to seal the system and vent air from the space outside to get our radon levels to be acceptable. His system was a complete waste of money.

Divide Colorado