There is so much imcorrect negative information about radiant barriers. If they did not work, NASA would not use them. You would not bake a potato in foil. Your can would not have it over the catalytic converter. Etc, Etc. Etc.
From BVileBound: "Unfortunately, 'radiant barrier insulation' is Snake Oil for most projects."
It's real. Check NASA, check Cal Tech, check ASTM, check dozens of others. Check California's department of energy. Ask them why some areas allow only radiant barrier as building insulation. Ask ANY physicist.
My own home's heating and cooling invoices before and after prove it, too. You should have witnessed the temperature drop in one room as I was installing it in the attic above. We also did extensive testing in one of the labs at work. It works to minimize heat gain and heat loss. It works as a reflector (97%) and a low emitter (3%).
In just one part of an NFL stadium in Michigan, the heating invoice dropped by 71.5% after adjusting for heating-degree hours. (The area was 6-sides concrete, 3 exposed walls, exposed roof and cantilevered floor.)
From BVilleBound: (2) The maximum insulation that 'reflective barrier' can provide inside a wall is R6 -
I don't want to pick a fight, but have no peaceful way of saying: When people speak of R value and radiant barriers, they are not fully educated about radiant barriers and certainly not about what R-value is measuring.
R-Value measures resistance to conducted heat flow from one area to another. Radiant barriers prevent radiated heat flow from one area to another. If a seller talks about r-value, run away. They are either scamming you or uneducated.
Quote From BVilleBound: (3) Note that the air gap MUST be sealed. So if you install a perforated reflective barrier, that sharply reduces the maximum R-6 value.
DO NOT PUT SOLID if a moisture barrier exists. You will trap moisture. Again- It isn't R-Value we care about.
(Quote From BVilleBound: 4) Reflective insulation is NOT effective in winter, because cold cannot be 'reflected'
Air is mass. The radiant barrier does not care at all about air. It cares about radiant energy. Radiant barriers are wonderfully effective in winter.
The room's objects (mass) radiate energy to the ceiling material. It conducts through the plaster and mass insulation to the foil that is laying in attic. The foil is a low emitter because there is a 19 mm or larger gap on the attic side, so the energy can not be emitted to the attic. After the mass insulation is saturated, the rest of the heat stays in the room. (Except for the 3% emission). When the room wants more heat, that which is trapped in the mass radiates into the rood. (Walk past a brick wall in winter just after the sun set. It's radiating the energy it absorbed during the day.)
It the foil were on the ceiling in the room, only 3% would go to the mass insulation.
Remember the difference between Conducted, Convected and Radiated energy and the concept of a radiant barrier will become clear.
Quote From BVilleBound: (5) You can also fasten a reflective barrier to the bottom of the rafters - to create a sealed air channel between the soffit and ridge vent.
Leave the bottom and top open so air can freely flow from the eave vents to the ridge vent. If you have pot vents instead of a ridge vent, build channels to vent all bays to the pot vents. This will take creativity.
Radiant barrier doesn't have to be sealed to work, but areas with gaps obviously won't reflect. The only time one should care about sealing it is if you are using it as a moisture barrier.
Regarding dust that BVilleBound mentioned, perhaps look at it like one more home maintenance project to vacuum the floor once in a while (like in 5 - 10 years). In one attic, I put the foil down and installed 3/4" sleepers on the joists, then the attic floor. Instant dust shield and the 19mm (3/4") gap were created.
I chose to go with the physicists and try radiant barrier. We also did testing at work with scale model buildings. I also have it at home. But, others are just as steadfast that it is hype.
This could argue forever. I just want Jsundmint (the original poster) to be aware of radiant; barrier's benefits so he or she can pick whichever insulation he or she feels is best for the project.
Paul