How to Insulate a Metal Building

A Complete Guide to Insulation Types, Placement, and Planning

Aaron Williams

December 1, 2025

If you're planning to build a metal structure—whether it's a workshop, barn, storage building, or even a barndominium—insulation should be high on your list of considerations. Without proper insulation, a metal building can feel like an oven in summer and a freezer in winter. The good news is that insulating a metal building is straightforward when you understand your options and plan ahead.

This guide walks you through everything you need to know: why metal buildings need insulation, the types available, where to install it, and how to plan your project from the start.

Why Metal Buildings Need Proper Insulation

Steel conducts heat about 400 times faster than wood. That's great for structural strength, but it means your building's interior temperature will closely track whatever's happening outside—unless you add a thermal barrier.

Beyond temperature control, insulation addresses another critical issue: condensation. When warm, humid interior air meets cold metal surfaces, moisture forms. Over time, this can lead to rust, mold, and damage to anything stored inside. Proper insulation with an appropriate vapor barrier prevents this problem before it starts.

The benefits add up quickly. A well-insulated metal building stays comfortable year-round, costs less to heat and cool, protects your equipment and materials from moisture damage, and even reduces noise from rain and hail on the roof.

Types of Insulation for Metal Buildings

Several insulation types work well in metal buildings, each with distinct advantages. Your choice depends on your budget, how you'll use the building, and whether you're insulating during construction or retrofitting an existing structure.

Fiberglass Insulation (Blanket and Batts)

Fiberglass remains the most popular choice for metal building insulation, and for good reason. It's affordable, widely available, and effective. You'll find it in two main forms: blanket rolls designed specifically for metal buildings and standard batts similar to what's used in residential construction.

Metal building blankets typically come with a vinyl or foil facing that serves as both a vapor barrier and a finished interior surface. They're designed to drape over purlins and girts, making installation relatively straightforward. Standard 2" fiberglass insulation provides roughly R-8 to R-11 depending on the product, while thicker options (4" or 6") offer higher R-values for buildings that need more thermal protection.

One customer in Choctaw, OK building a 40x60 workshop chose faced fiberglass blankets for the walls and roof. The project came in well under budget compared to spray foam alternatives, and the building maintains comfortable working temperatures through both summer heat and winter cold.

Spray Foam Insulation

Spray foam has gained popularity for metal buildings because it excels at air sealing—filling every gap, crack, and penetration as it expands. This makes it particularly effective at preventing condensation and maximizing energy efficiency.

You'll encounter two types: open-cell and closed-cell. Open-cell foam is less expensive and provides good thermal performance (around R-3.7 per inch) but requires a separate vapor barrier. Closed-cell foam costs more but delivers higher R-values (R-6 to R-7 per inch), acts as its own vapor barrier, and adds structural rigidity to the building.

The tradeoff is cost. Spray foam typically runs two to three times the price of fiberglass, and it requires professional installation. For buildings that will be climate-controlled—like a barndominium, office space, or temperature-sensitive storage—the investment often pays off through lower energy bills and superior comfort.

Rigid Foam Board Insulation

Rigid foam boards (polystyrene or polyisocyanurate) offer high R-values in a thin profile. They work well for specific applications in metal buildings: insulating under concrete slab floors, adding continuous insulation over girts to eliminate thermal bridging, or creating insulated interior walls.

While rigid foam typically costs more than fiberglass per square foot, it can be the right choice when space is limited or when you need insulation that won't compress or sag over time.

Reflective and Bubble Insulation

Reflective insulation (including "double bubble" products) works differently than mass insulation like fiberglass or foam. Instead of slowing heat conduction, it reflects radiant heat—making it particularly effective at reducing solar heat gain through the roof in summer.

These products are thin and easy to install, often used as a supplemental layer alongside other insulation. On their own, they provide limited R-value, so they're typically not sufficient as primary insulation in climates with significant heating needs. But as part of a system—especially for reducing summer cooling loads—they can be quite effective.

Insulated Metal Panels

Insulated metal panels (IMPs) are premium products that combine exterior metal skin, foam insulation core, and interior finish into a single panel. They install quickly, look clean, and perform exceptionally well.

The cost is significantly higher than other options, which makes them most common in commercial and industrial applications. For a high-end project where appearance and performance are both priorities, they're worth considering.

Insulation Comparison at a Glance

Type	R-Value per Inch	Relative Cost	DIY Friendly?	Vapor Barrier	Best For
Fiberglass Blanket/Batt	R-3.0 to R-3.8	$	Yes	Faced products include it	Budget projects, workshops, storage
Spray Foam (Open-Cell)	R-3.5 to R-3.7	$$	No (professional)	Requires separate barrier	Air sealing, irregular spaces
Spray Foam (Closed-Cell)	R-6.0 to R-7.0	$$$	No (professional)	Built-in	Climate-controlled spaces, barndominiums
Rigid Foam Board	R-4.0 to R-6.5	$$	Yes	Some products include it	Slab floors, thermal bridging
Reflective/Bubble	R-1 to R-2 (+ radiant)	$	Yes	Acts as radiant barrier	Supplemental, summer heat reduction
Insulated Metal Panels	R-6.0 to R-8.0	$$$$	Professional recommended	Built-in	Commercial, premium projects

Where to Insulate Your Metal Building

A complete insulation job addresses three main areas: the roof, the walls, and any openings or penetrations. Each has its own considerations.

Roof and Ceiling Insulation

The roof is usually the highest priority. Heat rises, so in winter you lose warmth through an uninsulated roof. In summer, the sun beats down on that metal surface all day, turning your building into a solar oven.

For new construction, fiberglass blankets are commonly draped over purlins before the roof panels go on. The facing creates a vapor barrier and finished ceiling in one step. For retrofits or higher-performance needs, spray foam applied to the underside of the roof deck provides excellent results.

Whatever method you choose, proper vapor barrier placement is essential to prevent condensation problems. In most climates, the vapor barrier should be on the warm side of the insulation—typically the interior.

Wall Insulation

Wall insulation works similarly to roof insulation. Fiberglass blankets fit between wall girts, with the facing toward the interior. The key is ensuring continuous coverage without gaps that would create thermal bridges or condensation points.

For buildings with interior liner panels, insulation installs between the exterior metal skin and the liner. This creates a clean, finished interior while hiding the insulation from view.

We often advise customers to think through their wall insulation plan before ordering their building kit. Specifying the right girt depth upfront—to accommodate your chosen insulation thickness—is much easier than working around limitations later.

Doors, Windows, and Penetrations

The best wall and roof insulation won't help much if air leaks freely around doors and windows. These areas deserve careful attention:

• Weatherstripping around walk doors and overhead doors

• Proper flashing and sealing around windows

• Sealing around any plumbing, electrical, or HVAC penetrations

• Insulated overhead doors for climate-controlled buildings

Insulating During Construction vs. Retrofitting

The timing of your insulation project significantly affects your options and costs.

New Construction Advantages

Insulating during initial construction is almost always easier and less expensive. You have full access to the framing before exterior panels go on, making it simple to install blanket insulation and ensure complete coverage. You can specify framing depths that accommodate your desired insulation thickness. And labor costs are lower because there's no working around existing finishes or tight spaces.

If you're ordering a new building kit and know you'll want insulation, plan for it from the start. Talk with your building supplier about the insulation you intend to use so they can help ensure your kit is designed to accommodate it.

Retrofitting an Existing Building

Already have an uninsulated metal building? It's still very possible to add insulation—it just requires a different approach.

Spray foam often becomes the most practical choice for retrofits because it conforms to existing structures without requiring perfect access to framing cavities. It can be applied directly to the underside of roof panels and interior wall surfaces, providing both insulation and air sealing in a single application.

For batt installation in an existing building, you may need to add interior framing to create cavities for the insulation. This adds cost and complexity but can be worthwhile for larger buildings where spray foam would be prohibitively expensive.

If your existing building has condensation issues, address the source of moisture before insulating. Adding insulation over a moisture problem will only make things worse.

Choosing the Best Insulation for Your Project

With so many options, how do you decide? Consider these factors:

Budget: Fiberglass blankets offer the best value for most metal building projects. If you're working with a tight budget, a well-installed fiberglass system will serve you well. Spray foam costs more upfront but can reduce long-term energy costs significantly.

Building use: A storage building for lawn equipment has very different needs than a workshop where you'll spend hours, or a barndominium where you'll live. Storage-only buildings can get by with minimal insulation or none at all. Work spaces benefit from moderate insulation (R-13 to R-19). Living spaces typically warrant higher R-values and careful attention to air sealing.

Climate: Hot climates benefit from reflective barriers and adequate roof insulation. Cold climates need higher R-values throughout. Regions with high humidity require careful vapor barrier placement.

DIY vs. professional: Fiberglass blankets and batts are manageable for most DIYers with basic tools and some patience. Spray foam requires specialized equipment and expertise—plan on hiring a professional installer.

For a typical workshop or hobby building, faced fiberglass blankets in the R-13 to R-19 range usually hit the sweet spot of cost and performance. For barndominiums or other climate-controlled spaces, many builders opt for spray foam in the roof and walls, or a combination of fiberglass walls with spray foam at the roof for maximum condensation protection.

Planning Your Insulated Metal Building Project

The most important advice we can offer is this: think about insulation early. The decisions you make when ordering your building kit affect what insulation options work best and how easy they'll be to install.

Consider your intended use for the building. Will it need heating or cooling? Will you be spending extended time inside, or is it primarily for storage? Your answers shape everything from R-value requirements to whether a vapor barrier is critical.

Work with your building supplier to ensure your kit accommodates your insulation plan. Discuss framing depths, liner panel options, and any accessories like vents or skylights that affect insulation installation.

If you're not planning to install insulation yourself, get quotes from insulation contractors before finalizing your building order. They may have recommendations that influence your kit specifications.

Ready to Start Planning?

At Indaco Metals, we've helped thousands of customers plan and build metal structures—from simple storage buildings to fully finished barndominiums. Our sales team can walk you through every step of the process, including guidance on preparing your building for insulation. We're also happy to connect you with experienced contractors in your area who can handle insulation installation.

Use our 3D Builder tool to visualize your project, or contact our team to discuss your specific needs. You can also visit our showrooms in Shawnee or Sand Springs to see our materials firsthand and talk through your project with our local experts.

Shawnee: 3 American Way, Shawnee | (405) 273-9200

Sand Springs: 17427 W 9th St, Sand Springs | (918) 419-6053

With nearly 30 years of experience serving builders across the region, we're ready to help you create a metal building that will stand strong—and stay comfortable—for generations.