Do You Need Furring Strips for a Metal Roof

Metal roof owners and installers often ask whether furring strips are necessary. This article explains what furring strips do, when they are recommended for metal roofing, installation methods, alternatives, and cost considerations to help make an informed decision. Furring strips can improve ventilation, drainage, and attachment options, but they are not always required.

Situation	Furring Strip Recommended?	Key Benefit
Installing Over Solid Sheathing	Usually Yes	Creates air gap and drainage for condensation control
Direct To Open Purlins	No	Panels can be screwed directly to structure
Retrofit Over Existing Roofing	Often Yes	Provides level surface and thermal break

What Are Furring Strips And Why They Matter

Furring strips are thin, narrow boards or metal channels fastened across roof sheathing or purlins to create a level, raised surface for attaching roofing panels. They form an air space beneath the metal panels that aids ventilation and moisture management.

Furring strips vary in material—wood, treated lumber, or metal—and in thickness from 1/2 inch to over 1 inch depending on the application and local codes. Choosing the right material and spacing affects roof performance and longevity.

Benefits Of Using Furring Strips With Metal Roofing

Improved Ventilation: The air gap created by furring strips promotes airflow under panels, reducing condensation risk on cool nights or in humid climates.

Better Drainage And Moisture Control: Furring strips create a drainage plane for any trapped water or condensation, directing moisture away from the sheathing and insulation.

Thermal Isolation: By separating metal panels from the substrate, furring strips reduce heat transfer and thermal bridging, which can improve comfort and reduce energy loads.

Smoother Surface For Attachment: Uneven sheathing, old roofs, or retrofits benefit from furring strips that provide a uniform nailing surface and allow correct panel alignment.

When Furring Strips Are Recommended

Furring strips are recommended when metal roofing is installed over continuous sheathing such as plywood or OSB and the installer wants to create a ventilated roof assembly. They are also advised for retrofit projects where a thermal break or improved drainage is required.

In colder climates or mixed climates where condensation forms on metal panels, furring strips combined with proper ventilation significantly reduce moisture problems. Condensation control is a primary indicator for using furring strips.

When installing insulated metal panels or using high-R insulation directly under panels, furring strips may be necessary to maintain air space and prevent compression of the insulation. They preserve insulation performance and panel fastening integrity.

When Furring Strips May Not Be Necessary

If metal panels are installed over open purlins or a ventilated roof deck, furring strips are often unnecessary since the structural members already create airflow and attachment points. Direct fastening to purlins can be more cost-effective and simpler.

Some modern metal roofing systems include built-in thermal breaks or factory-designed underlayment that provide drainage and ventilation, reducing the need for separate furring. Always check manufacturer installation guidelines before skipping furring strips.

Types Of Furring Strips And Materials

Wood Furring Strips: Usually pressure-treated lumber for durability and rot resistance. Common sizes include 1×2 or 1×3. Wood is economical but can warp if not properly installed.

Metal Furring Channels: Galvanized steel or aluminum channels are dimensionally stable and resist moisture. They are used where fire resistance or long-term stability is desired. Metal channels offer consistent spacing and reduced maintenance.

Composite Or PVC Strips: Used in corrosive environments, composites resist rot and pests but cost more. They are ideal for coastal locations where salt air accelerates decay.

Installation Best Practices

Start by checking the metal roof manufacturer’s installation instructions and local building codes. Manufacturer requirements dictate fastener type, spacing, and whether furring strips can be used.

Place furring strips perpendicular to the metal panels and space them according to panel span ratings—commonly 16″ to 24″ on center for many panels. Proper spacing ensures panel support and prevents sagging.

Use corrosion-resistant fasteners sized to penetrate the structural members while avoiding overdriving. Flashing, underlayment, and vents must integrate with the furring plane to maintain weather tightness. Sealing transitions and fastener heads helps prevent water infiltration.

Ventilation And Condensation Control

Combining furring strips with intake and exhaust ventilation creates a continuous airflow path under the metal roof. Typical solutions include soffit intakes and ridge vents positioned to align with the furring-created cavity. Balanced ventilation is crucial to prevent stagnant moisture buildup.

In cases where venting alone is insufficient, a vapor retarder or breathable underlayment can help manage moisture movement while allowing drying to the exterior. Select materials compatible with the roofing system and climate.

Alternatives To Furring Strips

Direct-To-Purlin Installation: Metal panels fastened directly to purlins eliminate the need for furring but require properly spaced structural members and may change roof aesthetics.

Raised Seam Or Standing Seam Panels: Certain standing seam systems incorporate clips and thermal breaks that create airspace without separate furring strips. These systems rely on manufacturer-specific attachment hardware.

Adhesive or Spacer Pads: For small projects, spacer pads or adhesive strips can create minor separation but do not provide the same structural support or ventilation as full furring strips. They are best for low-risk, limited applications.

Cost Considerations And Budgeting

Material costs vary by type: wood is the least expensive, metal channels cost more, and composites are highest. Labor increases when adding furring strips because of the extra fastening and alignment work. On average, adding furring strips increases project cost by 5–15% depending on roof size and complexity.

Long-term savings may offset upfront costs by reducing condensation damage, preventing mold, and extending the roof system’s lifespan. An investment in proper ventilation and drainage often reduces maintenance and repair expenses.

Building Code And Warranty Implications

Local building codes may require ventilation or specify attachment methods for metal roofs. Inspectors often look for proper fastening, flashing, and fire resistance. Noncompliance can lead to failed inspections or insurance issues.

Roofing manufacturers typically include installation requirements in their warranties that may mandate or prohibit the use of furring strips. Failure to follow those guidelines can void warranty coverage. Always document compliance with manufacturer instructions.

Common Mistakes To Avoid

Overlooking Manufacturer Guidelines: Installing furring strips against explicit manufacturer advice risks warranty denial and performance problems.

Poor Fastener Selection: Using non-corrosion-resistant screws or incorrect lengths leads to leaks and fastener failure.

Insufficient Venting: Adding furring without proper intake and exhaust vents will not solve condensation issues and may trap moisture.

Frequently Asked Questions

Will Furring Strips Prevent All Condensation?

Furring strips improve drainage and ventilation but do not guarantee zero condensation. Combining them with proper ventilation, underlayment, and vapor management is necessary for best results.

Can Furring Strips Be Installed Over Existing Metal Roofs?

Retrofits are possible by adding furring strips over existing sheathing or insulation if the structure can support added layers. However, installers must assess load, attachment integrity, and flashing details before retrofitting.

How Thick Should Furring Strips Be?

Thickness depends on panel profile and ventilation needs; common thicknesses range from 1/2″ to 1-1/2″. Thicker strips create more airflow but may require longer fasteners and adjusted flashing details.

Key Takeaways For Decision Making

Furring strips are a recommended solution when ventilation, drainage, and a uniform attachment surface are needed for metal roofs. They are particularly valuable over solid sheathing, in retrofit scenarios, and where condensation has been a problem.

When panels are installed over open purlins or when manufacturer systems provide built-in ventilation or thermal breaks, furring strips may be unnecessary. Always follow manufacturer instructions and local codes to protect performance and warranty coverage.

Action	Recommendation
Installing Over OSB/Plywood	Use Furring Strips To Create Ventilated Airspace
Installing Over Purlins	Furring Often Not Required
Concerned About Condensation	Install Furring Strips With Balanced Ventilation