In the following document and enclosed materials we have attempted to put together some tools to make your job easier in the selection and use of the proper roof insulation for your specific project. We know that given the basic roof design configuration changes, increases in R-value requirements (Conditioned Buildings) and a concern for potential problems in large shell structure, such as moisture entrapment, it has made it difficult for both the Architect and Builder to make sound decisions based on fact. Specifically, when it’s hard to determine fact from fiction.

Based on our almost 24 years of combined construction experience, we have attempted to separate these two for you as follows:

Fiction: An aluminum foil “capsheet" (two sided foil product) creates condensation in panel decks which may result in severe damage to wood members as well as purlin and sub-purlin hangers.
Fact: Unless the foil is perforated, or held back 1/2" from the ends of the sub-purlins, it is first a vapor retarder, with almost a zero perm rating. Like any vapor retarder, it will trap pre-existing moisture in the wood which can eventually result in damage. Any other vapor retarder, such as that on a fiberglass batt, would create the same problem. The cavity, which includes the deck, sub-purlins, and purlins should have a moisture content between 15 - 19% maximum at the time of installation.

Fiction: The moisture content must be 10% or less at time of installation.
Fact: You would never insulate most warehouses, other than in desert areas, if you needed 10% or less. Kiln dry lumber is only required to be 15% or less (see moisture paper).

Fiction: You can use a single sided foil facing as a capsheet and it would perform the same as a two sided foil product.
Fact: A single sided foil facing, with the foil facing downward, would be less than 40% the R-value of a double sided foil, in either a 2 x 4 or 2 x 6 assembly. The only R-value would be R 4.55 for cooling and R 1.32 for heating.

Fiction: A white capsheet with foil on the top and a white polypropylene or vinyl on the bottom (facing inside of building) performs as well as a double sided foil product.
Fact: With the white facing the cavity below (facing inside of building) you would lose R 4.55 down (cooling) and R 1.32 up (heating) from the total assembly value. That would prevent you from meeting the required calculation for heating and cooling in many buildings.

Fiction: A perforated capsheet (two sided foil product with a kraft or scrim core material) has the same flame spread as the capsheet without holes.
Fact: Once you perforate a product it normally will increase the flame spread. You are now exposing the core material to flame and that may, or may not, increase its flammability. However, if it was a 5 (flame spread rating) before the perforations, and a 15 after, it doesn’t make any difference. It’s still a class “A" product with a flame spread rating less than 25, which is excellent. When in doubt ask the manufacturer, or insulation contractor, to furnish a flame spread test on the perforated product.

Fiction: You can’t achieve an R19, for cooling, in a 2 x 4 roof without installing a multilayer foil or batt that hangs below the sub-purlins.
Fact: You can install a R15 high density, unfaced, fiberglass batt with any foil facing below and it will give you an installed R-value of R19.5 down and R16.32 up. That would normally be adequate in most southern California heating/cooling calculations (other than the desert or a building with lots of glazing).

Fiction: You can’t install an R30 fiberglass batt into a 2 x 4 panel deck and make it look good.
Fact: An R30 unfaced batt can be installed with almost any type of facing you desire without being crushed into place with wire. We do many retail stores such as PetsMart, Circuit City and many others with either a WMP-10, WMP-30 (White facing) or a WMP-10/Black (Black facing) installed around an R30 unfaced batt. This utilizes minimum compression and provides an excellent finished look.

I could continue with the fact or fiction remarks regarding facings, specifically reflective products, but that would make this letter too lengthy and boring. If you get the feeling there is a lot you didn’t know about these products, you are not alone. There has been a lot of misunderstanding and a lot of misinformation regarding insulation assemblies over these many years. It is our job to assist you in making your insulation decisions based on the buildings use, and its location.

Enclosed you will find a collection of the finest quality, UL tested and approved, insulation facings and stand alone capsheets available. Lamtec is the nations leading supplier of these products to the insulation marketplace and we are proud to be their western distributor. We at Advanced Foil Systems pride ourselves, not only on the Lamtec products, but also our ability to provide technical assistance to the Architect, Developer, Builder and Insulation Contractor. Please feel free to use our services whenever necessary.

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