If anyone can help...I'm wanting to build an icf walled, metal skinned sip roof with galvalume metal roofing, etc. The question I have is that I am wanting to use a radiant stem walled slab in north Florida and have been told contradictory advice on using foam isulation under the slab. I've got the land, plans, builder, etc. and one shot to get this right. Any advice would be appreciated. Larry

Assuming the stem wall is ICF, I can't imagine an insulated slab would be the right way to go on N. FL, where the cooling season earth-coupling of an uninsulatated slab would have greater benefit than the miniscule heating-season savings. Insulating the stem wall is the right thing always.

I'm not sure that a full-radiant slab makes a lot of sense here either, since the typical heating loads are so low the slab temp won't ever reach the cushy cruisin' in yer socks appeal. Assuming its hydronic, using spot-radiant- concentrate the radiant in places where you're likely to be standing/sitting walking and run somewhat higher water temps to get the necessary BTU output gives you the cush-factro better than a monolithic evenly-space full slab approach running at lower temps. The difference in efficiency between 100F water and 85F water isn't huge (whether heat pump or condensing boiler), but the feel under foot is. The efficiency difference using electric radiant will be near-zero. But whether hydronic or electric, if you go with the higher-temp spot-radiant approach and the radiant is less than 40% of the total slab area, it may make sense to put R5 under the radiant portions of the slab.

I agree that a radiant slab may be overkill for Florida. However, if you are going to put a hydronic heating system in your concrete slab. I would advise to put insulation below the slab. This makes sense for the simple reason that it will increase the efficiency of the radiant heat. With insulation below the slab the heat will be forced to move up into the concrete floor and less heat will escape into mother earth. I still don't understand why you would need In-Floor heating in Florida, but to each there own.

I figured that I would receive some inquiries into why I would use radiant floors in north Florida. I just assumed that since I use my central heat unit during the winter, why not use radiant floors with a possible solar integration. It can get quite cold here in the winter and we are planning on stained concrete for the flooring with area rugs. thank you for any advice or tips you may have. Larry

one word:  Slippers.

Seriously? Slippers? Wait a second, for my heating; one word: "coat". Windows? "transparent". Thanks for the advice.

FE: Slippers; Sorry, couldn't resist.

I'm from a cold climate, heating dominant so we do our infloor a little differently than you would. But I would mention that you could do a certain amount of cooling with your radiant slab also, as long as you have humidity control and keep the temp above the dewpoint. In general I quite agree with Dana1 has said. Infloor can be a pricey way to go, and cost may outweigh the benefits.

A resource site I've found useful in the past is: www.healthyheating.com Again, tends to be aimed towards heating dominant climates, but they have the best info I've found anywhere.