Has anyone placed their water supply lines under the basement slab instead of within the framed walls? The house I'm having built is passive solar and earth-sheltered, basically a walk-out basement with a roof on that basement (no floors above). The contractor says it will be easier for him to install the cold and hot water supply pipes (PEX) in the concrete slab rather than within the framed walls. This isn't for radiant heating, simply supply lines to faucets etc. Is this a good idea?

One concern I have is not being able to access the pipes should changes be needed (such as an additional run). I'm not worried about damage to PEX within concrete, I know that's safe for 50-100 years+.

A second concern is heat loss from the hot water supply into the concrete. This isn't an issue during the winter -- the flooring is ceramic tile on the slab so it would be like radiant heating, in that the tap water would take longer to heat up but that heat would be warming up the floor. However in summer I'm afraid the concrete would wick away the heat from the pipe and make the floor warmer when I want it cooler. I could avoid this by placing the PEX in standard foam pipe insulation and then within the concrete -- is that a good idea?

Note that I have 5" of HD Plastispan EPS (R20) under the concrete, so I don't think I should worry about the pipes freezing, despite my eastern-Ontario location (think Minnesota). But are there some disadvantages I've missed? Should I go ahead with this?

If I do, should I insulate both the hot and cold supply lines before putting them in the concrete? Or would it be better to sleeve them in a larger pipe to make them accessible for maintenance? (I'm told I can't put pipe-wrap on them and then sleeve them -- too thick, and too much friction.)

Thanks for you help. I've been thrown this surprise twist with an answer 'needed' tonite as he wants to pour the slab on Thursday!
...Terry