Metal building insulation

A guide to building insulation options with pros and cons for each

Last updated: 23 May 2024
Metal Building Insulation (MIP)


Insulation serves several important purposes in metal buildings. Besides providing resistance to cooling in winter and overheating in summer, it also minimizes the buildup of condensation and reduces the level of outside noise. If you plan on heating and cooling a structure, a little extra expenditure on insulation will yield significant savings in long-run energy costs.


Insulation IS NOT included in the metal building kit package, and you (or your contractor) should obtain this separately.

What Are the Benefits of Insulating Your Metal Building?

Reducing Condensation

Steel walls and roofs of metal frame buildings conduct heat very well, and condensation is a serious problem. In winter, the warm interior surfaces of uninsulated walls and roofs meet the cold air outside, and the interior air cools down near those surfaces. Because warm air contains more moisture than cold air, the excess moisture is released as condensation on cold interior surfaces of metal roofing and siding.

Some areas of buildings, such as kitchens, bathrooms, and laundries, are additional sources of moisture. Moisture could be emitted by concrete slabs and foundations that aren't fully cured.

Depending on the amount of condensation, it could drip down – and sometimes be mistaken for roof leaks! A common result of condensation is rusting of metal surfaces and fasteners. Condensation can also lead to mold and dampness in building finishes, which is both unpleasant and may be a health hazard, especially for those suffering from respiratory conditions.

While insulation – particularly the common fiberglass insulation – reduces heat transfer between warm and cold surfaces, it does little to prevent the movement of moisture-laden warm air through it. As a result, even a thick layer of porous insulation does not prevent condensation. Insulation must be coupled with an effective vapor retarder to slow down the movement of air through it.

Visualize an impervious layer of some plastic-type sheeting material – that’s what a vapor retarder might look like. The retarder can be laminated to the insulation or provided as a separate sheet. Properly designed and installed insulation, combined with a quality vapor retarder, helps protect the structure from condensation and its side effects.

Temperature Control

Choosing the right insulation for your metal building helps reduce energy consumption and, in some states, allows those constructing the building to claim tax incentives for saving energy.

Steel panels alone have little insulating value, meaning they offer no real protection from heat and cold. Adding the right type and amount of insulation helps control the interior temperature so that the building stays cooler in warmer months and warmer once the temperature drops.

spray foam metal building insulation

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Insulation Efficiency

Understand Local Code Requirements

As with the rest of your project, you must know and understand your local area’s code requirements for insulation from foundation to roofing. Over the years, code provisions have become more strict, and separate energy codes have been adopted in many states. Meanwhile, insulation technology has improved. Research is ongoing, including a focus on air leakage in metal buildings.

Your local code will specify the minimum amount of insulation needed for your project, and your contractor will help you choose the best insulation system for your particular project and given local weather conditions.

R-Values and U-Values for Metal Building Insulation

It’s important to understand what R-values and U-values are. Simply put, an R-value measures the insulation’s thermal efficiency – it quantifies the power of insulation to prevent heat transfer. An R-value refers to the thermal performance of a particular insulation product. The more effective a layer of insulation is, the higher its R-value. By contrast, a U value measures the thermal performance of a particular assembly.

The table below shows the respective R values for different thicknesses of fiberglass blankets and other common types of insulation.

However, it’s important to note that fiberglass blanket insulation is not the most efficient choice in a metal building. Various insulation material options are available, and new technologies are being developed as thermal resistance and energy savings become more of a concern in green building design. Below, from the Insulation Fact Sheet (DOE, 2002) are the R values for some common insulation materials expressed in R-value per inch of thickness.

Thickness Fiberglass Foam Board Insulated Panels Spray Foam
2" R-7 R-12 R-16 R-12
3" R-11 R-15 R-25 R-18
4" R-13 R-18 R-33 R-24
5" R-16 R-21 R-41 R-30
6" R-19 R-24 R-49 R-36
Cost Rating $ $$ $$$ $$$$

What are the Most Common Metal Building Insulation Options?

Fiberglass Blanket Insulation (a.k.a. batt insulation)

The most common type of insulation used in metal buildings because of its low cost and ease of installation, fiberglass blanket insulation has the added benefits of being both fire and sound resistant.
The insulation is outfitted with a vapor retarder and tested for fire safety, as well as odor, mold, and moisture resistance. The vapor retarder doubles as a finish on most building ceilings, and because of that, the outward-facing side is typically white in color for better light reflectivity.

Advantages: easy to install, low installation cost, approved air barrier.

Disadvantages: heat conduction at each purlin and girt reduces the overall R-value. Special rigid insulation spacers can be used to reduce this “thermal bridging."

Fiberglass Blanket Insulation

Fiberglass Blanket Insulation

Spray Foam Insulation

Spray-on foam insulation is made by mixing liquid components that react once mixed together.

Advantages: When properly applied, it fills the air gaps to reduce any air leaks, creating a tight building envelope for improved energy efficiency.

Disadvantages: More expensive than fiberglass. It requires a professional installer. Lacks vapor retardance and will absorb moisture or oily residue, precipitating corrosion of metal surfaces.

Metal building insulation - spray foam on walls and roof

Spray Foam Insulation
Credit: Spray On Foam & Coatings

Insulated Metal Panels (IMPs)

IMPs are available in various colors, sizes, and finishes, giving you almost any look for offices, banks, warehouses, industrial facilities, hospitality, healthcare, and more. IMPs can add a distinctive look to your building.

Advantages: Insulating quality is outstanding. Panels are lightweight and easy; one-step installation saves field-assembly time and cost.

Disadvantages: Relatively high cost; expertise is needed for installation.

Insulated Metal Panels (IMPs)

Installed Insulated Metal Panels (IMPs)

Foam Board Insulation

Foam-board insulation is rigid insulation that traps air in the foam's individual cells. Some local building authorities will require additional flame retardant facing, such as gypsum board.

It can be applied inside and outside your structure and can be finished with various treatments to fit your desired appearance.

Advantages: Thermally efficient, vapor-retardant, and dimensionally stable. Easy to trim and works well for flat roofs.

Disadvantages: Rigid insulation is more expensive to manufacture and install than fiberglass blanket insulation and will lose some insulating value over time.
Additionally, rigid insulation lacks the sound resistance of fiberglass blanket insulation.

2 Rigid Foam Board Insulation

2" Rigid Foam Board Insulation

Loose Fill Insulation

This type of insulation consists of loose fibers or fiber pellets. These fibers are blown into cavities with special equipment. Loose-fill insulation can be more expensive but fills corners better, reduces air leakage, and provides a better sound barrier. It’s generally used in walls, attics, and floors where it is applied by a moist-spray technique or a dry-pack process. Rock wool or fiberglass provides better coverage for steel structures. It is applied using a Blow-in-Blanket system that blows the insulation into open stud cavities. Loose-fill insulation has an R-3 to R-4 value per inch.

Advantages: Fills cavity well and reduces air leakage. Excellent sound barrier.

Disadvantages: It can be more expensive than some others; it might settle in vertical cavities.

Loose Fill Insulation

Loose Fill Insulation

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Metal Roof Insulation

The kinds of insulation described above can be used for walls or roofs, but there are some additional considerations.

Traditionally, a single layer of fiberglass blanket insulation draped over the purlins has been used. The insulation had a vapor-retarder facing at the bottom. This low-cost design no longer meets the energy codes because the blankets are squished over the purlins by metal roofing, and their insulating properties are greatly degraded. Essentially, a poorly insulated “thermal bridge” is present along each purlin line.

One method of increasing the R-value is to add another layer of fiberglass blanket insulation in the so-called “Sag and Bag” system. The second layer of unfaced material is installed over the first layer between each purlin. This design offers a low cost but provides relatively poor performance because of the heat-conducting thermal bridge along the purlins. And again, this method does not meet most areas’ energy codes.

Several roof insulation systems provide better performance in pre-engineered buildings, such as the two listed below:

  • Long tab and banded two-layer system.
  • Fabric liner/multilayer systems.

Long tab and banded two-layer system

The first layer of faced insulation is installed between the purlins and on the metal support banding. The second layer of unfaced insulation is then installed over the first layer.

Advantages: Relatively low cost for a high R-value system.

Disadvantages: Interferes with vital purlin bracing.

Fabric liner/multilayer systems

This approach has become very popular. The fabric liner is installed below the roof purlins, supported by metal banding. Then the first layer of unfaced fiberglass is installed between the purlins and over the liner system. The second layer of unfaced fiberglass is installed over the purlins and the first layer.

Advantages: Better thermal performance. Excellent air/vapor barrier. Excellent choice for retrofit projects.

Disadvantages: Difficult to install the first time. Other trades do not have easy access to the bottom flange of the purlins.

There are other metal building insulation options, some of which provide excellent performance but command premium prices.

Other Insulation Considerations


The part of the insulation that faces the inside of the building is known as the facing. Facing material must be carefully selected if it is going to be left exposed. In this case, the facing doubles as the inner finish of the wall or roof, so it typically needs to be reinforced with a layer of scrim (fiberglass or nylon mesh). This will increase its durability, protecting it from punctures and scratches. Because of its more vulnerable location, the durability of the wall facing might be even more important than that of the roof facing. “Birdproof” varieties are available for agricultural buildings.

It’s worth noting that the color of the exposed facing will contribute to the interior light level. With white or reflective foil facing, fewer sources might be required to illuminate the interior. Conversely, dark or black colors might be preferred for an intimate ambiance.
Facing Permeability

In fiberglass batt insulation, the facing acts as a vapor retarder. To minimize condensation, a vapor retarder with a low perm rating must be chosen. While plain vinyl has been popular in the past, it has very high permeability (its perm rating is 1.0) and thus does not provide protection against condensation. Vapor retarders with a perm rating of less than 0.1 will provide better protection against condensation for most applications. The best vapor retarders have even lower perm ratings, such as 0.02.

Liner Panels

Liner panels, available from some manufacturers, protect the insulation and provide a finished look to the interior of the building. The insulation is covered and protected with liner panels, which increases its durability. Liner panels can also provide lateral bracing for purlins and girts, which optimizes their structural performance.


Certain types of insulation cannot be shipped or installed in cold weather during winter. It is a good idea to ask the manufacturer about the material’s workability if a building is being erected in a cold climate.

Metal building insulation and liner panels

Metal building insulation and liner panels
Credit: Metal Construction News

Insulation FAQs

  • What is the best metal building insulation?

    It’s fair to say there is no ultimate “best”; the most appropriate insulation type depends on your building style, purpose, budget, and the level of insulation (R-value) required for your location.

    The best insulation for metal buildings is typically a material with a high R-value, such as spray foam or fiberglass blanket. Spray foam insulation is particularly effective for metal buildings because it forms a seamless barrier that prevents air leaks and provides good thermal resistance.

    Insulated metal panels (IMPs) provide the best insulation for commercial applications such as cold storage facilities. Be aware that there is low-quality insulation out there. Again, the guidance of a trusted construction professional may be the best way to go.

  • How much does metal building insulation cost?

    The insulation cost for your steel building will depend mainly on the type of insulation you choose and its R-value. Here are some rough cost estimates for the most common types of insulation used for steel buildings:

    • Fiberglass batts or rolls: $0.5 - $1.5 per square foot
    • Spray foam insulation: $1.5 - $2.5 per square foot
    • Insulated metal panels: $5 - $10 per square foot

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