Radiant suspended wood floor

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it sounds like those joists are way over spaned! Ideally you would have additional spot footings under the posts you plan on adding. You may not need more posts if you can pick up some of the over span with walls below.

Maybe get an engineer to give you some options?

As for the floor I would consider a plate installation from below as you re-configure the support. Or one of the on top methods. You could get a much beefier insulation package in the joist bays below, instead of a 1" foamboard method you are considering.

The more systems I install, the more I have become impressed with low mass, quick performing dry systems.

It also takes the tile cracking issues away and eliminates expensive cleavage membranes and funky tile to gyp challanges.

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John Hall_2

radiant suspended wood floor.

I need professional advise. I want to do in floor radiant on the first floor. Existing floor is 3/4 plywood over 2by 8 joists on 16" centers with a span of 13 ft. from the outside block wall to the steel beam in the center of the house, and then another 13 ft span to the other outside block wall. The beam is 40 ft long with two steel support posts. This floor is springy and barely strong enough as it is. The desired finished floor would be ceramic tile due to wear and tear from two overly active German Shepherds.
Ceiling height is not an issue. During remodeling I allowed 3 " of thickness for a new floor. The options I see are 2by4 sleepers with 3/4"to 1" foam board, sand and tubing in between covered by 3/4 plywood and tile. Or 1 1/2" gypcrete and tubing over 1" foam board covered with tile. Or the same thing but with lightweight concrete.
I plan to beef up the existing floor joists by building a new 2 by 4 wall in the basement at the midway point on each of the 13 ft spans with a concrete footing under it. Also addind three more steel posts under the steel beam. This should take the extra weight of any of these options. I know that heat transfer would be better with gypcrete/concrete options. There is an existing heat pump in case the radiant output is not high enough, but that would tend to defeat the purpose. My question concerns the need for control joints and potential cracking of the tile. I know very little about concrete, but it seems to me that control joints would be needed and that would probably lead to cracks in the tile over the joints. Also, would a concrete slab compress the foam board over time and cause cracks? Any thoughts on this? I would greatly appreciate your comments.