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What is the most cost-effective insulation under a heated slab? Pink board? Would a rdiant (foil) barrier help? My materials disributor is pushing a radiant barrier only 5/16 or 5/8″ thick by TVM that he claims is R10!! Anyone know anything about this? Hard to believe the R value. Under a slab, what is more important, rdiant barrier or thermal resistance? My code requires R15 24″ from perimiter; should I continue that for whole floor, or is R10 rigid (or R5) enough on inner portions? Climate-NW pacific.
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I used 2" pink board under the entire slab of my radiant heated floors with good results. From a practical standpoint, a thinner material will not hold up very well to the construction process (I have seen 1" insulation that ended up with broken sections from the concrete pourers walking on it during construction).
One could argue that perimeter insulation is all you really need to prevent heat loss but I think there is an advantage to full floor insulation in terms of more rapid responce. One of the few problems with radiant heat is the slower responce times and good subfloor insulation helps this considerably. I can get my room temps up to the thermostat levels within 1-2 hours over my slab (I bet it would be much slower without interior insulation).
*Jim is right about the response times - especially in a slab, much less so with gycrete on a framed floor or staple-up. But there is also a continuing loss down into the ground. The highest rate occurs at the start, but it does continue.R10 in 5/16" or 5/8"? Maybe an aerogel but those aren't even being used in refrigerators yet, much less construction. Ask to see the manufacturer's literature. I used 2" blueboard under my radiant slab, the whole area plus vertical perimeter.Foil surfaces only do any good if there is an air gap next to them. Since the soil will be tight on one side and the concrete on the other, the foil will serve no purpose. Get the sand base very flat (and of course well compacted). Then you will have less problems with breaking insulation during the pour.Make a diagram of where all the tubes go. Just use 1/4" graph paper and make 1/4" = the 6" grid of #10 WWF. Takes 30-40 minutes but can be really helpful later.Think about what rooms you want to warmest (bathroom, changing room) versus coolest (bedrooms, workshop) and run the tubing from one to the other. Because the hottest water is at the beginning of each loop. Consider running 150-foot loops instead of using the whole 300' box in one loop. It makes for a slightly larger manifold but provides sightly faster response and more uniform heating.If someone argues for uniform loop length, ignore them. It is more important to have each zone heated and controlled independently. You don't want one zone to be hot enough but some tubes from another zone still heating it.Make sure the thermostat are specifically for radiant slabs. Regular thermostats have much too wide a differential and don't track the rate of change of the room temperature. Also the tempering valve for the radiant water ideally adjusts based on the outside temperature (cold weather gives hotter water in the tubing). -David
*eps is the most cost effective insulation under a slab... look for 1.5 or 2 lb/cf density...we always used to use blue board and pink board... but the studies now prove that eps is much more cost effective .. so IF you have the space...(dig deeper )go with eps...
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What is the most cost-effective insulation under a heated slab? Pink board? Would a rdiant (foil) barrier help? My materials disributor is pushing a radiant barrier only 5/16 or 5/8" thick by TVM that he claims is R10!! Anyone know anything about this? Hard to believe the R value. Under a slab, what is more important, rdiant barrier or thermal resistance? My code requires R15 24" from perimiter; should I continue that for whole floor, or is R10 rigid (or R5) enough on inner portions? Climate-NW pacific.