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Top FAQs for Metal Building Insulation

Here are some of the most important issues for keeping fiberglass insulation working at its maximum.

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March 16, 2015 |
Jim Place

Fiberglass is an excellent, cost-effective insulator. However, if it is mishandled or installed improperly, its performance can be seriously degraded. These top FAQ’s in metal building insulation, originally published on the Star Buildings Insight Warehouse blog, highlight some of the most important issues for keeping fiberglass insulation working at its maximum.

My fiberglass insulation got wet during installation. Is it ruined?

Testing has shown that fiberglass insulation that has gotten wet from rain or snow during installation may recover its full R-value if :

The wet insulation is able to dry completely

It recovers its original thickness

It is determined no contaminants that would support mold or mildew have gotten into the fiberglass.

It is, however, difficult to ascertain whether or not the insulation has dried completely or if it has fully recovered its original thickness if it has gotten wet enough to compact.

It is crucial that there are no contaminants in the water that will contribute to mold or mildew growth. Fiberglass insulation that has gotten wet from storm or floodwater should be removed and replaced, as these sources have a high probability of containing contaminants that support the growth of mold or mildew. 

Can I paint my facing?

While most manufacturers do not recommend painting facing, it can be done in a few common cases. It is important to remember that, when facing is painted, its UL fire rating is no longer valid and the paint may potentially flake and fall off the facing over time. For more detailed information, including a guide on how to paint the exposed side of a vapor retarder, visit Lamtec’s website.

What causes condensation in my metal building?

Condensation that forms on a metal surface inside the building or on the interior side of the facing on the insulation is caused by the moisture that is dissolved in the air (water vapor) coming in contact with a surface whose temperature is at or below the condensation (dew) point. (The condensation point is dependent on relative humidity.) The vapor condenses at the place of contact and is seen as liquid water.

Condensation on the interior surface of a vapor retarder is evidence that the vapor retarder is relatively effective: the water has not gotten through the retarder and into the fiberglass insulation (which would ultimately reduce the effectiveness of the insulation).

When condensation forms on the interior surface of a roof or wall panel, behind the insulation, then water vapor has either gotten through or around the vapor retardant facing. It can get through a vapor retarder if the vapor pressure between the interior and the exterior of a building is too great or if a vapor retarder with an insufficient perm rating has been used. Water vapor can get around a vapor retardant facing wherever there are holes in the facing, where insulation splices have not been properly made, or where the facing has not been adequately sealed around necessary penetrations such as plumbing and/or electrical fixtures.

What are the longest, widest and thickest rolls of fiberglass metal building insulation I can purchase?


A more relevant question would be, “what is the most realistic maximum length of faced insulation roll that I can purchase?” We have learned that we are capable of producing rolls much too large and heavy to be handled on a job site. We have had instances where people have stated that the long roll lengths they had asked for were too cumbersome to be practical in the field. Therefore, as a guide, consider that the most realistic maximum roll lengths would be for 2” thick, 300 linear feet (282 pounds); 3” thick, 270 linear feet (368 pounds); 4” thick, 240 linear feet (414 pounds); 5” thick, 225 linear feet (455 pounds); 6” thick, 210 linear feet (497 pounds); 8” thick, 140 linear feet (435 pounds); and 9” thick, 100 linear feet (425 pounds).


Standard roll widths of metal building insulation are 36”, 48”, 60”, and 72”.
72” is the widest insulation we laminate.


Standard metal building thicknesses are 2”, (R-7), 3.4” (R-10), 3.7” (R-11), 4.3” (R-13), 5.3” (R-16), 6.3” (R-19), 8.0” (R-25), and 9.25” (R-30). 9.25” (R-30) is the thickest metal building insulation that can be purchased. While Utility Blanket is available only in the 2” thickness, both Certified R and MBI Plus are available in the thicknesses mentioned above, with the exception of 2”.

What is the density of fiberglass metal building insulation?

Read More on the Star Buildings blog, Insight Warehouse.

Jim Place | Metal Building Trends

Jim has spent over 35 years in the metal building industry, more than 20 of them as District Manager for Therm-All, Inc. Jim is Therm-All’s Elaminator System manager and he also heads up a committee within Therm-All tasked with development of new systems to more efficiently install High-R insulation systems. Jim is also a board member of the Mid-Atlantic Chapter of MBCEA and serves as treasurer of that chapter.

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