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Unregistered
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| 04/01/2006 3:28 PM |
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I was told by a gentleman who knows basically everything you can know regarding radiant heat. He says that it is a waste of money insulating your concrete slab, That instead spend your money on better windows. Yes the insulation will help shorten the initial startup to bring the slab up to the required temperature but once it has reached this temperature it basically stays at it with insulation or not. I originally was going to look at Insultarp, they have documentation that their product provides a R10.
Any thoughts from people in the know?
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NRT.Rob
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Posts:359
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| 04/01/2006 4:43 PM |
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Insultarp is about an R1.65, not an R10. Ignore their sales lit. Two studies both put the kabosh on that claim, and also their basic claim is just ridiculous: you have NO radiant transfer from a slab to the ground. None. Period. You have conductive transfer, which their product is horrible at stopping. Radiant transfer only occurs through space, and any radiant barrier needs a good 1-3" of space to work.
Whether you need slab insulation or not depends. You most definitely need insulation on the vertical outside edges of your slab. That is a significant source of heat loss. You also need to insulate the outer 5' perimeter of the slab, where it is still seeing higher loads from the surrounding ground surface.
As for the center of the slab, if your ground is clay, rock, or wet, you definitely want to insulate fully. Those conditions can make for a heck of a heat sink. I saw a slab up here in maine (built on ledge, which is everywhere up here) that literally could not maintain temperature in the spring when the ground was wet. wicked all that heat right out.
If you have good natural drainage, no standing water, no high water table, and good loose or sandy soil, then you could get away with less or no insulation in the center of the slab. If you're in doubt though, you should insulate. That's not an easy mistake to fix later. You can replace windows.
Even in that case though, you do lose heat to the ground unless you are maintaining ground temperature or lower for a slab temp. Perhaps not enough to pay for the added insulation quickly.. but something, yes.
We generally go with a reduced center insulation or none only on very large slabs (where it's mostly center area), or in mild areas with the above noted soil conditions. In a normal residential slab, I don't think it's worth trying to "play the dice" there unless you are very sure of your soil conditions year-round and your water table. And even then, you're not going to save that much since the perimeter and edges still need to insulated, no matter who or where you are.
Hope that helps!
-=Northeast Radiant Technology, LLC=-
www.NRTradiant.com |
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-=Northeast Radiant Technology=-
NRTradiant.com |
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Unregistered
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Posts:2321
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| 04/01/2006 6:09 PM |
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I received documentation from Insultarp which was backed by an engineering firm analysis. I can send it to you if you would like. It confirms the R10. It does not sound plausable but its in black and white. I am all confused now.
BTW I have not poured my basement yet. I put down about 8" of bluestone crusher run. When the plumber dug down a couple of feet for a toilet he hit water. Does this mean I should definitely add insulation? I have ICF walls so would this cover me for verticle insulation?
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Unregistered
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Posts:2321
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| 04/01/2006 6:34 PM |
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Insul tarp is a total waste of money under the slab ! Conduction occurs through any material & that stuff is so leaky it should be reserved for applications where it can reflect heat passed through an air space NRT-Rob knows what he is talking about . My experience as Mech Eng says forget it
Invite your know it all gentleman here for an education - He obviously knows enough to get you in trouble.
Will the water stay down two feet or rise up (suck heat) & flow away?
Just thinking a decent test MIGHT be to add colouring to the water & see if it flows away. If it does you definitely need underslab insulation to prevent extreme heating cost .
My system (Legalett -- http://www.legalett.ca--- used in Sweden for years does full design for you & they know the right questions |
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Unregistered
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Posts:2321
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| 04/02/2006 12:28 PM |
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It is too late in the project to look at any thing else besides hydronic radiant heat. If 2" hard insulation was used what would keep it from getting all broken up by men trampling all over it during the poor? What would anyone thing of spraying a 1-2" layer of closed 1.7" foam. Would this serve both an insulator and vapor barrier? Thanks.
BTW I beleive he may be a regular contributor to this website regarding not insulating the basement slab (as long as its not a walk out basement)
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Unregistered
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Posts:2321
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| 04/03/2006 11:06 AM |
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Jimbeam, Regarding the 2 part sprayed foam, We use this in School construction on the west coast We use in on the roofs. I ALSO gets a waterproofing paint atop the foam. I had the guys spray 10" of the stuff into the bildge of my boat. Given enough time it will still take on and retain water. Just my 2 cents worth.
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NRT.Rob
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Posts:359
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| 04/03/2006 12:02 PM |
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This is what RIMA (the reflective insulation manufacturer association) has to say about their type of product under slabs, in a fairly recent study:
"In order to more fully understand the influence of reflective insulation materials in concrete floor systems, RIMA obtained the services of a consulting firm specializing in thermal performance (R & D Services, Inc.). Thermal efficiency calculations were used to generate an estimate for a typical case involving reduction in heat loss for a common concrete floor system. The calculation is based on steady-state thermal conditions with an isothermal plane at the heating pipes and a plane between the gravel and the ground. The ground temperature was 55 degrees Fahrenheit, while the temperature of the heating pipes was 125 degrees Fahrenheit. The calculation assumes two inches of concrete (R-0.10) below the heating pipes, and five inches of gravel (R-0.75). A reflective insulation material (R-1.10) is located between the concrete and the gravel (the total thickness of the concrete floor system is roughly nine inches). The system R-value of R-1.95 results in an energy savings or reduction in heat loss of 56% when compared to the same concrete floor system without insulation. It is important to note that the calculation used to generate the example described above does not include any additional thermal benefit resulting from the aluminum surface(s) of the reflective insulation material. In other words, the reflective insulation material is performing similar to a non-reflective insulation material [ASTM C 168, ASTM C 727, and ASTM C 1224 define a reflective insulation as a thermal insulation consisting of one or more surfaces having an emittance of 0.1 or less, which equates to a reflectance of 0.9 (90%)]."
It is an R2, IF you count the resistance of concrete, crushed stone, etc. Anyone claiming anything else is either lying, or giving you misleading information hoping that you will misinterpet it. A seperate study in canada recently also confirmed the low performance of these products. Beyond that... I'll word myself more carefully this time ;)... the basic thermodynamics involved are quite simple. Radiant transfer is heat transfer through space. You have no space here. Thus, radiant transfer is not present and cannot be effectively blocked by a radiant barrier. Conductive transfer is transfer between two objects that are touching. THAT is what you have under a slab, and the only thing that fights that is good old R-value. Not R-value "equivalence", not reflectivity, but simple R-value, resistance to conductive heat transfer. I'm not trying to jump on you, but this claim is old and totally false.
2" of rigid foam is the standard. It has its flaws, but ultimately it works. I don't know that I would try to be a pioneer. If your plumber hit water that easily, do NOT take chances. I hope that helps!
-=Northeast Radiant Technology, LLC=-
www.NRTradiant.com |
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-=Northeast Radiant Technology=-
NRTradiant.com |
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jipp
Registered Users
Posts:3
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| 11/02/2006 1:31 PM |
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That confirms my doubts for cetains applications( without air gap in front) of reflective insulations.
Thank you NRT.rob
and here is the link of the referenced text for the ones interested:
http://www.rima.net/pdf_files/TB101-UnderConcreteSlabs.pdf
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