Rigid Foam Plastic Insulation

One of the joys of what I do is I get to learn new things every day. I’ve often thought to myself, the day I stop learning, is the day I am dead.

In today’s lesson….one of our clients has taken his engineer sealed plans to his Building Department to obtain a building permit. The building is designed with interior steel liner panels (not my personal favorite choice – but a topic for a future blog). The panels are to cover fiberglass insulation.

Sounds pretty straight forward so far, at least to me…..

Until our client told the Plans Examiner he is going to insulate the building using rigid foam plastic insulation.

What is rigid foam plastic insulation? An example would be Rmax’s R-Matte Plus-3, which is a rigid foam plastic thermal insulation board composed of environmentally sound, closed cell, polyisocyanurate foam bonded to a durable white-matte (non-glare) aluminum facer and a reflective reinforced aluminum facer. Basically – any polyisocyanurate sheathing.

The plans examiner came up with the following, “…foam plastic shall be separated from the interior of a building by an approved thermal barrier of 0.5-inch gypsum wallboard or equivalent thermal barrier material that will limit the average temperature rise of the unexposed surface to not more than 250 degrees F after 15 minutes of fire exposure, complying with the standard time-temperature curve of ASTM E 119…”

In layman’s terms, if your idea is to insulate your new pole building using polyisocyanurate insulation boards, plan upon having to place ½” drywall on the inside wall. This may result in costs which were not budgeted for, not just for the drywall, but to have the framing and weight capacity of the building designed to be able to support it.

My recommendation? Compare total costs between this and other options, such as fiberglass, before making a commitment to rigid foam plastic insulation.  It’s not that it is a bad choice – not at all.  It’s just that your building needs to be designed to support it.  And of course, your buildings need to meet the code for it so your plans examiner is in happy-land.

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