Specials!

Moisture Warnings for Radiant Barriers

Florida Solar Energy Center Warning!

“Placing the material directly on top of insulation is not recommended. In this type of installation, dust will accumulate on the foil surface facing the roof. In time, the dust will negate the radiant barrier effect. An exception to this is the “chip” and multi layer products on the market. Their multiple layers give them resistance to the effects of dust build up, making them suitable for floor installations. In all installations beware; problems could develop with moisture condensation”.

 

US DEPARTMENT OF ENERGY WARNING!

“A radiant barrier installed on top of attic floor insulation is more susceptible to dust accumulation. This undesirable installation method may also trap moisture in fiber insulation during cold weather. A radiant barrier installed on the cold side of the insulation acts as a vapor barrier in the wrong location. When warm moisture carrying house air leaks into the attic in the winter, it may condense on the underside of the barrier. Even a perforated radiant barrier can trap moisture in cold climates since the water can freeze in the small holes and seal them.”

 

Moisture Vs the Radiant Barrier

 To prevent moisture build up look for a Permeance (perm) of greater than 10.  The higher the perm number the better. HeatBarrier XP has a perm rate of 60.

Solid radiant barrier sheets are called “Vapor Barriers”.  A vapor barrier basically stops moisture from moving from point A to point B.  To be considered a vapor barrier the permeance must be below 1.0. Another way to view this is that a vapor barrier will “TRAP” moisture.

A good way to understand permeance and vapor barriers is  to think about putting a wood block inside a plastic bag the wood would still be wet months from now.  If moisture in its vapor form cannot pass through or object won’t “dry” then the product IS a vapor barrier. The block of wood would rot over time if it could not dry out. This is how sheet radiant barriers work. They block moisture and should not be used on top of insulation.

Why is this important?Moldy attic due to moisture build up

Virtually all (over 70%) of home issues are due to mold, mildew, rot, decay, etc. And moisture is the common theme here.  DRY products don’t grow mold, rot or decay. The bottom line is that moisture in wall and ceiling assemblies is not a good thing.  You want DRY walls and ceilings.

In cooler weather, the moisture INSIDE the home is greater than OUTSIDE. This moisture is given off by cooking, showers and normal perspiration and respiration. Since moisture will naturally move from wet (inside) to dry (outside) it will pass through sheetrock, insulation and then into a typical attic.  The LAST thing we want to do is TRAP moisture here.  Moisture, attic insulation and wood do not go well together.  A perforated radiant barrier (perm 5-10) will allow moisture to pass on through into the attic until the attic gets below freezing. When the attic gets below freezing the perforations in perforated radiant barriers will freeze shut. This then makes a solid sheet and will trap moisture.

 Solid products are usually not perforated and are a recipe for disaster when installed inside an attic.  Solid radiant barriers are a great product when used correctly in applications like metal buildings.  Sheet radiant barriers are often MISUSED in residential attics. This is especially true when foil products are laid directly over the attic insulation.  Moisture will pass through the sheetrock and will get trapped in the insulation below the bubble foil insulation.  This moisture will accumulate until it either condensates (turns to water) or freezes (turns to ice). Mold will rapidly grow in your attic.

Sheet radiant barriers work effectively throughout the south to block heat from entering the attic when placed over the rafters. In these cases the heat loss Applying multiple layers over your insulation improves your R-value.from inside the home in the winter has not been addressed but ignored. In the winter when you need to conserve the heat and reflect it back into your home a radiant barrier flake such as HeatBarrier XP must be used over the insulation. The exceptionally high perm rate of 60 will allow the moisture to fully escape the attic thus prevent mold!