How To Insulate An Existing Metal Building

By the Bull Buildings team · Updated October 2026

Learning how to insulate an existing metal building is one of the most cost-effective ways to improve performance without replacing the structure itself. Many older metal buildings were built with little to no insulation, or with materials that have deteriorated over time. Torn facing, compressed blankets, and exposed steel can lead to condensation problems, temperature swings, and wasted energy.

Yes. You can insulate a metal building after it is built. Retrofits usually use facing-covered fiberglass blankets installed between the wall girts and roof purlins. Spray foam and rigid foam board are alternatives where you want a thinner or sealed layer. The best fit depends on climate, framing, building size and use.

At Bull Buildings, we help customers evaluate retrofit insulation options by shopping across suppliers and matching the right materials to the building’s size, layout, and use. Retrofitting insulation does not just improve comfort, it protects equipment, reduces moisture issues, and extends the life of the structure.

Why Retrofitting Insulation Matters

More than half of all metal building insulation projects today are retrofit applications. That number continues to grow as owners look for ways to improve existing buildings instead of starting from scratch.

Metal buildings can transfer heat and cold quickly, which affects comfort inside. Warm air escapes in cold weather, and heat pours in during summer months. This temperature imbalance causes condensation when warm air contacts cool steel surfaces, leading to dripping moisture, corrosion, and long-term damage.

Adding new insulation helps seal air leaks, increases overall R-value, and improves energy efficiency. In many cases, retrofitting insulation also qualifies as a tax-saving improvement, making it a smart financial move in addition to a practical one.

Common Signs Your Metal Building Needs Insulation

Existing metal buildings often show clear warning signs that insulation needs attention. Persistent condensation on walls or ceilings is one of the most obvious indicators. Rust forming on interior steel components is another red flag.

Other signs include large temperature swings, excessive noise inside the building, rising energy costs, or insulation that appears sagging, torn, or missing entirely. Addressing these issues early prevents more expensive repairs down the road.

How Retrofit Insulation Works in Metal Buildings

Retrofitting insulation typically involves installing new insulation blankets between wall girts and roof purlins. These blankets are factory pre-cut to match the building’s dimensions, which helps ensure proper coverage and consistent performance.

Facing materials are applied to the insulation to act as a vapor retarder. This facing not only helps control moisture but also improves interior appearance by giving walls and ceilings a clean, finished look.

Because metal buildings vary in framing layout, retrofit insulation systems are designed to adapt to different girt spacing, purlin depth, and bay widths.

Retrofit Insulation Steps at a Glance

1. Inspect the building. Note condensation, interior rust, and any sagging, torn or missing insulation. Fix leaks first.
2. Pick the method. Compare blanket, spray foam and board for your climate, framing and use (see the table below).
3. Measure the framing. Check girt and purlin spacing so blankets are pre-cut to fit, with the first girt about seven feet up the wall being a common layout.
4. Install with vapor control. Place the faced insulation so the facing works as the vapor retarder, with a base angle along the floor to secure the facing at the bottom edge.
5. Secure it. Use stick pins and washers, InsulHold coils or steel banding so the insulation does not sag.
6. Seal and finish. Close seams and edges, trim exposed pin tips, and check for gaps that could let warm air reach cold steel.

The details for each of these steps are covered in the sections that follow.

Wall Insulation Installation in Existing Buildings

Wall insulation installation depends largely on girt spacing. In many metal buildings, the first girt is located approximately seven feet above the floor, with upper girts spaced six feet apart or less.

When this configuration is present, insulation below the first girt is typically installed vertically, while insulation above is installed horizontally. A base angle is installed along the floor perimeter to secure the insulation facing and help create a moisture barrier at the bottom edge.

In buildings where all girts are spaced six feet or less, insulation is installed horizontally throughout. Pre-cut insulation rolls are labeled to ensure correct placement, which helps speed up installation and reduce errors.

Methods Used to Secure Retrofit Insulation

Several attachment methods are used when retrofitting insulation in metal buildings, depending on wall condition and design goals.

Stick pins are commonly glued to clean steel surfaces and used to hang insulation blankets. Once the insulation is placed over the pin, a friction washer holds it in position. The exposed pin tips are trimmed after installation, creating a quilted appearance.

InsulHold coils are another popular option, especially for retrofit projects. These coils grip the fiberglass insulation and prevent sagging over time. In some cases, additional support systems such as steel banding or liner panels may be used for added durability.

Roof Insulation Installation for Existing Metal Buildings

Roof insulation retrofits follow a similar principle but use different support systems. Metal building purlins are often spaced five feet apart, which aligns with standard fiberglass blanket widths. When spacing differs, insulation is factory cut to match the existing layout.

One of the most common roof retrofit methods is the banding system. Steel bands are fastened to the underside of the purlins at regular intervals, creating a grid that supports the insulation blankets. The pre-cut insulation is fed above the bands and secured in place.

This system prevents sagging and maintains consistent insulation coverage across the roof, helping reduce heat loss and condensation.

Refacing Old Insulation for Better Performance

In some cases, existing insulation is still structurally intact but has damaged or outdated facing. Refacing insulation allows building owners to improve moisture control and interior appearance without removing the original insulation layer.

This process involves covering the old facing with new facing materials or adding a new insulation layer with updated facing attached. Refacing increases overall R-value and gives the building interior a brighter, cleaner look, which can improve lighting efficiency as well.

Benefits of Retrofitting Insulation in an Existing Metal Building

Adding insulation to an existing metal building delivers multiple benefits beyond temperature control. Sealing air leaks improves energy efficiency and lowers operating costs. Increased R-value helps stabilize interior conditions year-round.

Improved condensation control protects stored vehicles, equipment, and materials from moisture damage. Reflective facing materials can enhance interior brightness, reducing the need for additional lighting.

From a value perspective, insulated metal buildings are more functional and appealing, which can positively impact resale potential.

Retrofit Insulation Options Compared

Here is how the common retrofit materials compare on R-value per inch and on how they handle moisture. R-value is the resistance to heat flow, so higher means more insulation for the same thickness.

Method	Typical R-value per inch	Vapor retarder (typical)	Retrofit notes
Fiberglass blanket or board	2.5 to 4	Depends on the facing	The usual choice between girts and purlins. Faced rolls double as the vapor retarder. Banding or coils keep it from sagging.
Mineral wool rigid board	3 to 4	Depends on the facing	Board form, so it needs a way to be fastened and sealed at the seams.
Expanded polystyrene (EPS) foam board	3.8 to 4.4	Typically Class III	Cut and fastened as board. Seal joints.
Extruded polystyrene (XPS) foam board	About 5	Typically Class II	A thinner layer for the same R-value as blanket.
Polyisocyanurate (polyiso) foam board	About 6	Depends on the facing, typically Class I	Highest R-value per inch of the boards listed.
Spray polyurethane foam (high density)	About 6	Typically Class II	Applied to the steel as a sealed layer. Installed by a professional crew.
Reflective barrier	Not listed in this table	Ask the supplier	Mainly reduces radiant heat. Ask the manufacturer for tested values for your building.

Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), “Typical R-values and Vapor Retarder Classifications for Common Insulation Materials,” last updated December 23, 2021. Checked October 2026.

Vapor retarder classes: Class I is 0.1 perm or less, Class II is above 0.1 and under 1.0 perm, and Class III is above 1.0 and under 10 perm. Thicker layers add R-value, so check the total R-value you need for your climate. For retrofit pricing, see our guide to how much it costs to insulate a metal building. If you are comparing options for a new building instead, read top 3 insulation options for your metal building.

Choosing the Right Retrofit Insulation Strategy

There is no universal solution for every building. Climate, building size, framing layout, and usage all influence the best insulation approach. Over-insulating can be unnecessary, while under-insulating leaves performance gaps.

Bull Buildings helps customers evaluate retrofit insulation options by comparing suppliers, materials, and configurations. Because we shop the market for you, we focus on practical solutions that deliver real performance without unnecessary expense.

Next Steps for Your Retrofit

Understanding how to insulate an existing metal building gives owners a powerful tool to improve performance without replacing their structure. Retrofit insulation addresses condensation, reduces energy loss, and enhances long-term durability.

With proper planning and the right materials, insulating an existing metal building can deliver immediate and long-term benefits. Bull Buildings is here to help guide that decision by finding the right solution at the right price.

Frequently Asked Questions

Can you insulate a metal building after it is built?

Yes. Retrofit insulation is usually installed between the wall girts and roof purlins, and can also be added as foam board or spray foam. Existing insulation with a damaged facing can often be refaced rather than removed.

What is the best way to insulate an existing metal building?

There is no single best method. Climate, building size, framing layout and how you use the space decide it. Faced fiberglass blanket is the most common retrofit, and the comparison table above shows how foam options differ on R-value per inch.

Do I need a vapor barrier when retrofitting insulation?

Metal buildings are prone to condensation when warm air meets cool steel, so retrofit insulation needs a vapor retarder. Faced blankets include one, and foam products have their own vapor retarder class (see the table). The right class depends on your climate and the building use, so confirm it with your insulation supplier or local building department.

How much does it cost to retrofit insulation per square foot?

It depends on the method, the R-value, the building size and whether you hire an installer. We do not quote a single per-square-foot figure here because it varies too much. Read our insulation cost guide and ask us for quotes from several suppliers.