Hi, any pointers on this would be very helpfull. I have a 16' x 21' sunroom open to our home and will be getting a 2.5-3" slab poured on top of the existing slab ( to encase pex radiant ). I intend to add a few inches of insulation over the existing slab and fix pex to wire mesh. I have windows on 3 sides that start 19" above the floor and go to 8' high so I will also place radiant in the 19" high perimeter walls. Should I put small 1/2" cement squares to raise the mesh and do I need a vapour barrier as well, If so, should it run up the walls? 6 mil poly? Thanks in advance for your info, I hope I've explained myself properly. GC. *info* The room works very well right now but the heat loss from the windows is too great. 11" step down into room & vaulted ceiling at house connection ( height reduction is not an issue ) Full below frost foundation but unsure if insulated below slab. permitter walls are 2 layer of brick with 2" of spray foam insulation? SORRY, I can't figure out how to carriage return

They make insulated panel designed to be placed on uninsulated slabs that holds the PEX. I think you can even only do a 1.5" pour over it. In any event I think I would just staple the PEX to the insulation and just put the mesh or rebar above the PEX.

i usually install the wire mesh and tie it all together with rebar ties. I then flip the mesh over and install the pex again with rebar ties (it is quicker and holds better then zip ties and is cheaper). Then I flip it back, seems hard but it is not. the pex is best at the bottom of the slab for even heating and this will put the mesh a half inch off the insulation where it should be for strength. You should do 2 loops so can do this procedure in two sections.

What flooring are you installing? If it is tile I would skip the radiant in the walls, or just skip it period. My current house is very well insulated at ICF R30 and R60 ceiling and the floors aren't very warm because the house doesn't use much heat. My old house is R19 stud and uses a lot more heat and the floors are toasty warm trying to keep the house warm.

I believe code for window is if it is closer then 18 inches to the floor the glass has to be tempered. You are at 19 now and safe but if you add a few inches you are going to have to change all the windows to tempered glass if they are not now.

Put some plastic down for the vapor barrier is the best.

The carriage return problem is caused by your browser. If you are using EI switch to Chrome or the other way around. The Quick Reply box at the bottom always works for me and it is only a problem when you start a new message.

Don't use the insulated panel icfbound suggested. They are expensive and don't save time.

Where are you located? If you don’t have insulation under the existing slab, you might need more insulation than you are currently planning. Yes, window areas need more heat gain than non-window areas. You can accomplish that as part of the HR floor heating system design, augment with HR wall panels or also do mini splits, an especially nice option (or a total solution) if you also need AC in the Summer. Comfort level is largely a function of the MRT (Mean Radiated Temperature) of your surrounding area. You need to have a good room by room heat loss analysis to properly design a HR floor heating system.

To elaborate on the above info; what is the orientation of the room and how are you going to heat the water?

We used plastic "chairs" to raise the mesh up. In your case just having the tubes on top of the wire would work fine.

You could make the tube spacing closer together around the perimeter near the windows.

Thanks to you all,

icfbound:
to maximize storage mass I prefer not to use the pex-holding insulation and will be using flat insulation although the pucks would hold the wire mesh above the bottom.

newboston:
I have the rebar fixing wire but cannot imagine how I’ll flip over 340 square ft. even separated in 4 sections, I intend to run 4 lines, closely spaced to boost output to combat the massive heat loss. I intend to leave the floor at polished concrete. I will defiantly look into the window height issue, it never occurred to me. I agree with setting the pex a bit lower for even heat but I also see an issue with putting the it directly at the bottom, wouldn’t the radius of the pex cause larger breaks than mesh at the bottom of the slab and it wouldn’t be fully encased in cement


sailawayrb:
I’m in Montreal, when I get the install date from the cement contractor I’ll drill through the slab to hopefully find insulation but if I don’t, I doubt I’ll be able to change plans that late. Presently, We throw a carpet down in the winter and the floor is bearable.
What I forgot to mention was that this room structure foundation ( and thus floor ) are exposed 18” above grade so cold wind whipping around really freezes the floor ( the opposite of a sauna rock I guess)

I do need Ac in summer, massively, but intend to install sun shading elements on the outside of the home. That also equates to winter heat gain that I’m not taking advantage of by covering my concrete/tile floors with carpet

The room faces West with windows on North and South as well.
It will be tied into an existing system of closed loop Solar Evacuated Tubes ( heat pipe) with electric backup. floors run off of heat exchangers in 2x120 gal off grid storage tanks

Heat loss calcs come in between 53 and 60 BTU/ft that I’ll never achieve but the room has a 34,000BTU epa wood stove for the colder times

ChrrisJ: How close did you place the chairs? did it give the cement guys a headache? I can see them walking around rebar but wouldn’t it it be a pain with wire mesh?
I ask only because I would like to have the mesh a bit higher than bottom.

If your floor is exposed to outdoor conditions in Montreal, you really should have something like 2-4" of EPS insulation under the floor and along the floor perimeter sides. A HR floor is typically 5-20F higher in temperature than the indoor temperature, depending on how well insulated and sealed the building is. So you will have an enormous floor heat loss and a very inefficient heating system if you don't properly address this.

It did give at least one of the 3 guys a headache. He stomped around like a jerk, Wish I would have said something to his boss(Father). Later on he hit one of the pex-Al-pex tubes with the fan blade type machines.

I sort of blamed my self, we didn't put any pvc pipe over the tubes to protect them where they came up for the slab.

The chairs were an inch and a half, so with the tube on top of the mesh the tubes were in the middle of the 4" slab. Really didn't use very many chairs so the mesh sagged a lot.

Be sure to insulate the perimeter of the slab, we cut the top to a 45* angle.

I have used 10' x 6' sheets of wire mesh and flipped sections with well over three hundred square feet. Here is a picture of a very complex one we did. It is not that hard with two guys.

https://photos.app.goo.gl/VAP5cqo53cPQL1g56

Wow, that operation would make me very nervous...chute concrete and using wheelbarrows over mesh and PEX. We always pump concrete and use strongly chaired rebar so our guys can walk the rebar. The HR slab in these photos was done with 1/2" PEX placed in 4" thick EPS Nudura Hydrofoam, #4 rebar 12" OC and finished with a 5" thick 4000 psi pumped concrete slab that was stamped to look like heavy green slate stone.

Wow, well here are two examples that work....one that cost way to much and one that fits everyone's budget. Not sure if I should say your project is over engineered or overdone because of little engineering.....you definitely have money to waste but nice job.

I am not scared doing it this way one bit. The tubes are all pressurized for safety, it didn't look like yours are but could be wrong picture looks like it shows loose tubing.

The Borst job looks very well done to me. You can see the pressure gauge in second photo and that nurdura foam is the insulated panel stuff I suggested earlier. The Newbostonconst job looks like amateur hour to me...but whatever rocks your boat...

Sorry, I didn’t intend to offend. I was just surprised to see the manner in which you poured that HR slab. That approach has a much higher risk of PEX damage and failure, either during the pour or in subsequent years. Rebar and mesh have sharpies that can damage the PEX. That approach also requires about the twice the labor and associated cost. For $300/pour we get a pump truck and a person to pour the concrete.

This home was engineered for a 9.2 seismic event and the additional cost to achieve that was about 1.5% of the home cost. Additional rebar and strong concrete is readily and reasonably obtained where we construct. I would agree that if you are in a location where you don't need or want this increased structural capacity, it could be avoided.

The PEX in previous photos was largely held in place by the inherent design of the Nudura Hydrofoam and we also stapled it too. We always pressure test the system at 80 psi for 24 hours prior to the pour and maintain this pressure during the actual pour. Then we reduce the pressure to what it will be when the system becomes operational (typically about 20 psi) and then we maintain it at this pressure until the system actually becomes operational. As Icfbound indicated, you can see a pressure gage in the second previous photo and you can also see a pressure gage in this photo of the completed manifold station which is located in an office in a central location of this single level 2400 sf passive solar home. This was a seven zone, ten circuit HR system which uses a 4 kW NextGen HR appliance (about $1,500) for its heat source and HR control panel which is located in the mechanical closet of the home which also contains the central vacuum, HRV and tankless domestic water heater systems.

No offence taken....I just look at the cost of doing it that way and smile.

Wire mesh lends itself well to getting the one foot spacing needed for the tubing and puts the tubing and the mesh where I want them. This keeps everything low in the slab which guarantees the tubes wont get hit when the slab relief cuts are made and that the slab is heated evenly. This house is/has 7300 sqft which I am guessing saved at least $5000. We have 5 zones and 29 circuits.

We have zero requirement for rebar in slabs so you wouldn't use my method as I would never use yours.

I think I understand where you guys are coming from and the intended result with regard to your differing ways of proceeding with the pex and mesh.
A vapor barrier under it all would be a must also, right. or over the insul?

I'll ask another one regarding the install, given the differing views on the web I hope we can all agree . Polyiso seems to be a big NO across the board with regard to under slab because of it's water wicking and retention quality but does have the a higher R value than EXP and EPS.

This is all happening in a now conditioned area of a home that other than a cold room is avery livable and not exposed to ground humidity.
Can a properly installed ( all joints sealed ) layer of polyiso be used for it's greater isolation from the slab below?


thanks,

I don't think Polyios can support concrete. I would have plastic under the concrete but don't know your cross section of your floor.

i am guessing your cross section currently is:
ground
air
floor joist
osb
cement

You are proposing:
ground
air
floor joist
osb
cement
insulation
cement with pex

If this the case you could insulate from underneath and put cement on cement. There is a plus and minus to this.

The down side is the thicker the slab the slower it reacts. Like a 6 inch slab can take 6 plus hours to heat up. So most of use keep the thermostat at one temp.

The up side of the thick slab is it will absorb a lot of heat from the windows helping to keep the room cool and use that heat it stored to keep the room warm into the evening.

I'm all for the thicker slab even with longer heat up time, that's the effect I'm going for, but it would be impossible for me.

My cross section is not quite as you specify.

The room has a foundation that goes 3-4' below grade and sits on a footing.
The foundation protrudes about 2' above grade
It is backfilled with gravel then has a slab floor poured.

The city plans I was able to get show an insulation layer between the gravel and the pad but I cannot just assume that this was done as I don't see any in a corner I dug up a bit. I need to dig lower to be sure.

I was going to add

Vapour Barier
Insulation
Cement with pex

If I forego the insulation just to realize there's non placed below the pad, I'm gonna lose all the floor's radiant and passive heat

Did you say earlier you could drill a hole to see what insulation might be there.....?