What Size Furring Strips For Metal Roof: Ultimate Guide To Choosing The Best Furring Strip Dimensions For Metal Roofing Installation

Choosing the right size furring strips for a metal roof is a critical decision that affects roof performance, durability, and longevity. Whether you are re-roofing over shingles, installing new construction, or optimizing ventilation and support, understanding furring strip sizes ensures effective installation and prevents costly mistakes. This detailed guide explores recommended dimensions, materials, installation techniques, and industry standards for American homes and buildings.

Key Factors To Consider When Choosing Furring Strip Size

Furring strips are narrow wooden or metal strips used to create a level surface for attaching metal roofing panels. Selecting the ideal size involves evaluating several factors:

• Load-Bearing Capacity: Ensures the strips support the metal panels without sagging or bowing.
• Spacing Requirements: Impacts ventilation, insulation performance, and roof structure.
• Substrate Conditions: Influences whether additional thickness or width is needed to compensate for irregular surfaces or overlays.
• Regional Building Codes: Dictate minimum sizes and attachment methods.
• Roof Slope and Panel Type: Affects stress distributions and anchoring needs.

Standard Furring Strip Sizes For Metal Roof Installation

The most common furring strip sizes for metal roofing in the United States are 1×3 inches and 1×4 inches. Actual finished dimensions (after milling) are slightly smaller, typically 0.75 inches thick by 2.5 or 3.5 inches wide.

Nominal Size	Finished Size	Typical Use
1×2	0.75″ x 1.5″	Light-duty, soffit or small structures
1×3	0.75″ x 2.5″	Standard roof overlays, moderate snow load
1×4	0.75″ x 3.5″	Heavy roof overlays, higher snow/wind regions
2×4	1.5″ x 3.5″	Commercial/heavy-duty residential

When To Use 1×3 Vs. 1×4 Furring Strips

1×3 furring strips are appropriate for most residential applications, especially when installing metal roofs over existing shingles or decking in areas with moderate wind and snow loads. They provide sufficient support and are easy to handle and fasten.

1×4 furring strips offer enhanced structural support for regions with heavy snow, severe wind, or when longer panel spans are required. The added width distributes weight and fastener stress more evenly across broader surfaces.

Minimum Thickness And Width Recommendations

For optimal fastening and performance, the minimum recommended thickness for furring strips is 0.75 inches (nominal 1-inch). Width should be no less than 2.5 inches (nominal 3-inch) to ensure sufficient anchoring area for metal roofing screws and prevent splitting or cracking of the wood.

Do not use strips thinner than 0.75 inches or narrower than 1.5 inches, as these may not provide adequate holding power or resistance to weather effects.

Material Choices: Wood Vs. Metal Furring Strips

Most installations in the U.S. utilize pressure-treated wooden furring strips such as Southern Yellow Pine or Spruce-Pine-Fir. Pressure treatment protects against rot and insect damage, especially important in roof applications exposed to condensation or moisture.

Metal furring channels (usually 25-gauge galvanized steel) are used for commercial, fire-resistant, or high-moisture environments, providing extra longevity and stability. However, they require specialized fasteners and are often more expensive.

Spacing Furring Strips For Metal Roof Panels

Spacing depends on the structural requirements, weight of the panels, manufacturer recommendations, and the anticipated roof load. The most common furring strip spacing is 24 inches on center (OC), but 16-inch spacing is often used for heavier panels or areas with high winds.

• 16-inch OC: Superior strength for heavy panels or severe climate zones
• 24-inch OC: Acceptable for most lightweight roofing systems and moderate conditions
• Greater than 24-inch OC: Not recommended except for engineered systems or commercial buildings

Furring Strip Placement: Vertical Or Horizontal

Orientation is driven by the direction of the roofing panels:

• Vertical Placement: Used when installing horizontal ribbed panels, improving water drainage and roof ventilation.
• Horizontal Placement: Common for vertical panel systems, acting as direct supports for the panels.

Many experts recommend a vertical “batten and counter-batten” configuration, where vertical strips sit atop each truss/rafter and shorter horizontal strips are fastened across them, to maximize airflow underneath the metal panels.

Installation Tips For Furring Strips On Metal Roofs

• Fastening: Secure strips directly into the rafters or trusses with exterior-rated wood screws or ring-shank nails.
• Moisture Protection: Always use pressure-treated lumber or a moisture-resistant barrier between untreated wood and roof deck.
• End Joints: Stagger all end joints and avoid creating seams at the same location along the span.
• Pre-Drill Holes: Prevent splitting of the wood, especially at cut ends.
• Level Surface: Use a string line or laser level to ensure strips are flat and uniform before attaching the metal panels.

Building Code And Industry Standards For Furring Strip Size

The International Residential Code (IRC) Section R905.10 and manufacturers’ installation manuals set necessary requirements for size, spacing, and materials in metal roof installations. Always consult your local building department, as snow load, wind uplift, and seismic risk may require adjustments to furring strip dimensions or placement.

Code Requirement	Standard
Minimum Thickness	0.75″ (nominal 1″)
Minimum Width	2.5″ (nominal 3″)
Spacing	16″–24″ OC
Fastening	Screws or ring-shank nails, min. 1.5″ penetration

Installers should also verify that the furring system aligns with the roofing manufacturer’s warranty conditions.

Special Considerations For Insulated And Ventilated Metal Roofs

If installing above rigid foam insulation, a minimum 1×4 (0.75″ x 3.5″) furring strip is often recommended to allow for adequate fastening length and prevent compression of insulation below. For ventilated roofs, spacing and strip height must accommodate airflow as specified by ventilation standards—often ¾ inch minimum air gap over insulation.

Furring Strip Size For Overlaying Metal Roof On Asphalt Shingles

When retrofitting a metal roof over an existing asphalt shingle roof, 1×4 furring strips are typically advised. The increased width and thickness help span uneven shingle surfaces and provide a more forgiving substrate for attaching the new panels.

Lumber Grades For Furring Strips

Use #2 grade or better pressure-treated boards for residential roofing to ensure fewer knots, splits, and weak points. The wood should be straight, dry, and free of significant defects to create a secure underlayment for metal roofing.

Cost Comparison: 1×3 Vs. 1×4 Furring Strips

Size	Average Price (8′ Length, 2025)	Best Use Case
1×3 PT	$2.30–$3.75	Standard residential overlays
1×4 PT	$3.10–$4.80	Heavy snow/wind, uneven surfaces

Choose the size that balances structural needs with overall project costs, factoring in current lumber prices and local availability.

Fastener Selection For Furring Strips Under Metal Roofs

• Exterior-grade screws (galvanized, coated, or stainless steel): 2.5 to 3 inches for 1×3/1×4 strips into framing members
• Ring-shank nails: Minimum 2.25 inches to secure solidly through strip and into substrate

Using the correct fasteners is crucial for avoiding roof movement and long-term loosening due to temperature or moisture changes.

Common Mistakes When Sizing Furring Strips For Metal Roofs

Do not undersize furring strips in an effort to save money, as inadequate support compromises the lifespan and performance of your metal roof. Other common errors include spacing strips too far apart, using untreated or low-grade lumber, failing to use an approved moisture barrier, and ignoring code requirements for the specific wind or snow load zone.

Using Metal Furring Channels: When And Why

In situations with extremely high humidity, fire risk, or commercial applications, metal furring channels may be used. Typical sizes are 7/8-inch by 2.5-inch galvanized steel channels, installed either vertically or horizontally. They provide exceptional stability, do not rot or warp, and are compatible with steel panel installations using self-drilling screws or clips.

Adapting Furring Strip Size For Unique Roof Designs

Complex roof geometries, such as intersecting valleys, dormers, or curved sections, may necessitate custom furring strip sizing. In these cases, select wider or thicker strips for curved surfaces, maintain continuous support at valleys and ridges, and ensure the layout does not impede water drainage or panel locking mechanisms.

Frequently Asked Questions About Furring Strip Size For Metal Roofs

• Q: Can I use 2×2 or 1×2 for metal roof furring?
  A: Not recommended for primary roof support; minimum 1×3 is best for longevity and strength.
• Q: Do I need to treat wood furring strips?
  A: Yes, always use pressure-treated lumber or apply a protective sealant.
• Q: What if my roof deck is not level?
  A: Use wider furring strips and shim as needed to create a flat plane before panel attachment.
• Q: How often should screws be placed through the metal panels into the furring strips?
  A: Follow manufacturer specs, often each rib or seam, typically 12–24 inches apart depending on panel and wind load.

Summary Table: Choosing The Right Furring Strip Size For Metal Roofs

Roof Type	Strip Size	Spacing OC	Material
New Metal Roof, Moderate Loads	1×3	24″	PT Wood
High Wind/Snow, Retrofit	1×4	16–24″	PT Wood
Over Insulation	1×4	16–24″	PT Wood
Commercial/Fire-Rated	7/8″ x 2.5″ channel	16–24″	Metal

Final Thoughts: Matching Strip Size To Metal Roofing System

Ultimately, the best furring strip size for your metal roof installation will depend on your location’s climate, roof structure, metal panel specifications, and building codes. Always prioritize adequate width, thickness, and spacing—and when in doubt, consult with building professionals and reference manufacturer guidelines to ensure a secure, long-lasting result.