Hydronic radiant heat in a 10 \" slab.

It is important...

w/ that thick a slab to keep it in the middle part of the slab. This is done by using Chairs. Chairs are bent rebar that when installed will keep the steel mesh in the upper part of the pour...kpc

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Over the top

What is speced out for the slab reinforcment cindy?

An over the slab type system may be more efficient,for the pouring of the slab(pumped I believe your discription), and over all radiant system response/efficiency.

There are a few products out there for over the slab applications. You just have to plan them into the design.

Raupanel, Roth panel, Warmboard, sleeper system Gordy

Some Thoughts

Can you move?

Sounds like a serious project. Where is it -and can I guess? The climate is key. If Northern CA or the Pacific NW you have a steadier climate -better considering the mass you will have- than our eastern roller coaster of late.

The Radiant Panel Association is one source of information.

http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=471

John Siegenthaler and Robert Bean are both authors and sources not to mention resources in affilliation with the RPA. The work of both should be sought.


Setting the depth is done using chairs or stand-offs supported from the substrate or from the welded wire mesh. Might slab that thick may have two layers of mesh allowing the upper one to support the tubing matrix? Ask your structural engineer. I am assuming that this has to be monolithic for structural reasons. That said, might you consider a topping slab over the structural base? Will change your detailing but will keep the structural pour intact and give you a choice of floor finishes.

From a controllability standpoint, you understand I am sure that you will be warming up all of that concrete eventually. Part of me says, the deeper you are the more even the surface temperature and that is a good thing. If I had to punt I would say the middle of the slab but will leave this to more hands-on practitioners than I. The other part says, once warm you will not be able to shut it off right away. How much solar gain the space has will be a huge factor.

The reason I am waffling on the depth is, if the tubing is in the upper few inches of the slab, the slab beneath the tubing has to be warmed too, eventually anyway. You will get heat to your space faster but the boiler will run longer until the full mass heats up. Thus the center gets the nod to my thinking.

I would put it before the group, others with far more experience than I, what they would do.

Spend money on good anticipatory (PID) controls. Monitoring the slab warming/cooling rate over time relative to room temperature is critical. Little sips of tepid water over time. What you pump into your slab on Monday may not show up until Wednesday...your slab will weigh 117 lbs. per SF.

From a constructability standpoint my initial concern is the curing temperature of all that concrete. Not sure how hot it gets with that deep a pour compared to what PEX can withstand (180F and up). I personally would use PEX-AL-PEX (aluminum cored pex) for the higher pressure and temperature ratings. Also should the O2 barrier be abraded by the concrete, the aluminum is the barrier ultimately.

Anyway, sorry to ramble. I think I identified more problems than solutions... alas, it is late.

insulation

Don't forget the insulation! (under the slab)

are you building on a fault line?

Sell the property and move while you are still above ground.

Find another engineer.

bag the cement guy while you are at it.

really, you seem to have the worst of all possible help, until you showed up here:)

find someone who knows what they are doing to find you some incompetents to do the work.:) then you can blame him for everything that goes wrong.. and feel Good about it , knowing you weren't the person who hired them in the first place. That is so important in this day and age....having some one to whom to, firmly affix the blame...:)

It would not do you any good to direct the work from an arm chair...let me say though that the Japanese have had many a chance to rethink building so have the Alaskans..i have experienced plenty of earthquakes and a 2000 sq ft structure to an earhquake, is something, were it made of solid metal, that would likely fair no better as to its condition or its whereabouts thereafter...just a thought ....though not very uplifting.

i have poured some cement in my days, i happen to like slab on grade as a building practise. our most recent building has 3 foot wide Footing 16" deep with 16"X12"deep footings on the five transverse walls. the size is slightly 9X's the dimension of your slab. the depth of the slab is 4" over 2" of foam board.we drove some heavy equipment in to keeep it warm in 40 below...trust me on what i am saying....get some better help.

Structurally

(and I admit this is not my primary area of expertise), the slab may have to be cast in one monolithic pour for structural reasons. Bonding and dowelling of the layers may be an issue and the diaphragm and "beam depth" inegrity may not be assurable.
Otherwise, I agree, pour in lifts as you said, for shear constructability reasons.

Naturally, Cindy's structural engineer can better advise her.

My concern about temperature is the endothermic properties vary by thickness, sort of compounding. As Gordy points out, 100 degrees is not uncommon but that I associate with a 4" slab.

When pouring a proton therapy facility, the three, four and sometimes six and eight foot thick slabs of hematite-embedded concrete took months to cool.....

Brad

You are correct about the endothermic properties that is why I stated when PROPERLY CURED. I come from a more stringent spec. oriented enviroment. I have seen what commercial, and residential concrete can be subject to in the pour/ cure process.
Heavy, and Highway construction standards on the other hand..... the testers, and RE's are always there to make sure things are properly done. While some think of them as a monkey on ones back they are there to insure a top quality product.


Cindy is I'm sure up against a GC who has his own concrete contractor he uses all the time. Who wants to get in, get out, get paid with as little job related hassle as possible. Not sticking up for them merrily painting the picture.

As far as the tubing in that particular slab yes its doable as everyone has suggested...but is it the best option? I'm thinking, and only guessing her climate maybe tempid being in a earthquake zone. So is all that mass plus added controls to keep the fly wheel effect at bay the best option for her, and everyone involved.

Another option is ceiling radiant very delightful I must say.

Gordy

A decision has been made.

Well, always a little slow on the information highway here! Apparently the slab is a new type called a "tensioned" slab that uses some kind of cables and a million pounds of tension to engineer the slab and that has something to do with why they can't put the tubing in the slab. The structural engineer demeed a 2" over-pour is the way to go. Warmboards were considered, but were cost prohibitive, even though they are manufactured across the street from the development! Thanks for eveeryones input. Cindy

Had a feeling

that was to be one special slab... Seems like that slab will still be there, warm and toasty, after a 9.0... how comforting is that?

Ironic the proximity to the Warmboard factory!

Now your challenge, Cindy, is the insulation. As stated, edges are critical but so is the downward mass. If that structual slab is at least edge insulated, I suspect an R-5 may be OK below your topping slab but will still add an inch. I would do R-10 given an ideal situation but then you have a 4" total topping depth. Even the additional 1" of an R-5 may be an issue for you.

Good for you for going radiant. Keep in touch, send progress photos if you can.

Best heating system for your climate

The best heating system for your climate would be a good envelope with a bit of passive solar, and some really good windows. With 20F outdoor winter design, and an HRV, you should be able to heat the house with a few lights and body heat if the envelope is done right. In fact, using low temperature panel radiators with a little modulating condensing boiler would be as efficient as the big radiant slab. If you are absolutely in lust with the warm feet feeling, consider using capillary tubes in thin-set mortar beds under the few hard tiled floor zones (bathrooms), or electric heating mats (NuHeat), and see if the Governator will give you some grant $$ for a couple PV Panels and solar water heating panels while you're at it!