You absolutely must talk to your engineer and contractor about this issue.

I second holly springs.. If you cook even a reasonable amount, you will want a decent hood which will be a hulking thing hanging over the island and visually breakup your space. If you will have seating in the island then there is danger of hot pots with hands belonging to non-cooks.. 90% of the work is usually prep.. which can conceivably be a participatory thing for others using the island. IMHO prep area including prep sink in the island and cooking on the wall counter is a more pleasing and functional setup.

To run a gas line underneath, you have to get tile cutters to cut a channel in the slab that the gas line can go into and this area has to be filled-in, leveled before tiling. Tiling can happen after cabinetry unless you prefer to have the tiles under the cabinets as well. Definitely a contractor/ plumber discussion. You will likely run into code requirements as well. If you do want to have cooktop on the island, getting electricity there may be easier than getting gas.. so maybe an induction cooktop?

Lalitha

"To run a gas line underneath, you have to get tile cutters to cut a channel in the slab that the gas line can go..."

Good luck finding "tile cutters" willing to trench a post tension slab.

Unless you have a lot of money to burn move the cook-top to a wall.

No trade will touch a post tensioned slab without a structural engineer involved at every step. You just upped the cost of your kitchen remodel by several thousand depending on if what you want can be done at all.

It would be much cheaper and more functionally efficient to have a cooktop on a wall.

You'll need the floor xrayed before you can even consider whether or not you could even run the lines without hitting the tension devices.

-but-

A post- tensioned slab on grade is pretty rare - so maybe a bit more detail is needed. Is this some sort of Cali - earthquake design ???

At any rate - the people telling you it's $$$ just to get to a proposal are correct.

Better want it pretty bad.

If you insist on doing this, you're probably best off laying the gas line on top of the slab and rasing the floor the allow for the height of the gas line.
As for which material, black iron or the flexi-plastic stuff, the gas line should be made of, I couldn't say.
I fully agree with everyone else here.
You don't want to mess around with a post tensioned slab.

Idea: Use an LP Gas cooktop and have an island cabinet space for the 20-lb. LP Gas cylinder. Think about how long you can cook outdoors on your 6 burner patio grill before having to refill the cylinder. Actually many weekend cookouts worth of fuel. Check your local codes.

Old thread, I know.

LP gas cylinder INSIDE a house....?

Using a LP gas cylinder indoors is not only illegal, it is terribly unsafe.

And, to respond to other comments above, any gas line run in a concrete slab, or underneath needs to vented to the outside, you can't just notch the slab, run a pipe and cover it it up with thinset and tile.

Has anyone lowered gas pipe from the attic to the island?

gas line has to vent to the outside, just venting the pipe into an attic won't do it.

I am not talking about venting. I am asking about lowering supply gas pipe from the attic to the island. Already have gas furnace and gas water heater in the attic, but now want to replace electric cooktop with gas cooktop. The problem: it is located in the middle of the kitchen

I was in a house that blew up because of the propane tank inside. Propane connection broke and candles were being used at the time. Was woken up from dead sleep and in time to jump out a window right before the gas in the house ignited. And someone, NOT ME, had to go back into the house after it ignited to get the burning canister because the flames were then setting the roof on fire. Pains me as as I look at the electric range on my island.

"but now want to replace electric cooktop with gas cooktop"

@HouzzUser-60126775 - you should replace your old electric cooktop with an induction cooktop (powered by electricity) and save yourself grief, expense, and needing a master plumber to run a gas line and vent it properly. With an induction cooktop, you would be getting a faster more responsive easier to clean cooktop, and you'd be done.

Edited to add: just realized that @HouzzUser-60126775 posted a month ago, so is prob gone. I should not have been sucked in by @brettellis' post haha