1×4 or 2×4 for Metal Roof? Choosing the Right Lumber

The decision between 1×4 and 2×4 can significantly impact the structural stability, load-bearing capacity, and cost-effectiveness of your roofing project.

Whether to opt for the cost-effective and versatile 1×4 lumber or the robust and reliable 2×4 lumber can take time and effort.

With your roof’s integrity at stake, making the wrong choice could lead to structural issues and potentially costly repairs down the line.

The primary difference between a 1×4 and a 2×4 lumber is a 1×4 lumber actually measures 3/4 inch thick by 3.5 inches wide, while a 2×4 lumber is 1.5 inches thick by 3.5 inches wide.

In this guide, I will help you determine whether to use 1×4 or 2×4 for metal roof that suits your specific needs and requirements.

1×4 or 2×4 for Metal Roof – Which One You Need?

Understanding the difference between 1×4 and 2×4 lumbers is important to determine which one you need for your metal roofing project.

In this section, we will delve into the comprehensive differences between using 1×4 and 2×4 lumbers for metals roof.

Factors1×4 Lumber2×4 Lumber
Load-Bearing CapacityAdequate for smaller roofs and low-slope applicationsGreater load-bearing capacity for larger roofs and snow loads
Structural StabilitySuitable for lighter weight requirementsProvides enhanced structural stability
Spacing of Rafters/Purlins16-24 inches on the center24-48 inches on the center
Roof Design ComplexitySuitable for simpler roof designsPreferred for complex roof designs
BudgetMore affordable option compared to 2×4 lumberSlightly more expensive
Availability and SourcingWidely available and sourced without difficultyGenerally readily accessible
Long-Term DurabilityMay have limitations for long-term durabilityProvides better long-term durability
Maintenance and RepairsMay require more frequent maintenance or repairsOffers greater structural integrity for maintenance

When Should You Go for 1×4 Lumber?

Smaller Metal Roofs

For smaller metal roofs, such as sheds, garages, or residential structures with limited footprints, 1×4 lumber can be a viable option.

The lighter load requirements of smaller roofs can be adequately supported by 1×4 lumber, making it a cost-effective choice without compromising the roof’s structural integrity.

Low-Slope Roofs

Metal roofs with low slopes typically have less weight-bearing demands compared to steeper roofs.

In such cases, 1×4 lumber can provide sufficient support and stability, especially when combined with the appropriate spacing of rafters or purlins.

The lower cost and ease of handling and installation make 1×4 lumber a practical choice for low-slope metal roofs.

Milder Weather Conditions

In regions with milder weather conditions, where heavy snow loads or extreme wind forces are not major concerns, 1×4 lumber can offer adequate strength for the metal roof.

As long as the local building codes and regulations permit the use of 1×4 lumber, it can be a suitable option for these weather conditions.

Closer Rafter or Purlin Spacing

If you prefer closer spacing between rafters or purlins in your metal roof assembly, 1×4 lumber is a practical choice.

Due to its smaller dimensions, 1×4 lumber can provide the required structural support with narrower spacing.

This can be advantageous when you desire more precise control over the placement and attachment of the metal roofing panels.

Budget Constraints

Cost considerations play a significant role in any construction project. If you are working within a tight budget, 1×4 lumber offers a more affordable alternative to 2×4 lumber.

The reduced cost of 1×4 lumber can make a substantial difference, especially for larger roof areas, allowing you to allocate your resources more efficiently without compromising the roof’s functionality.

When Should You Go for 2×4 Lumber?

Larger Metal Roofs

For larger metal roofs, such as commercial buildings, warehouses, or expansive residential structures, 2×4 lumber is often the preferred choice.

These roofs tend to have more significant weight-bearing requirements due to their size and design.

The increased load-bearing capacity of 2×4 lumber provides the necessary strength to support the weight of the metal roofing system and any additional loads, such as snow or equipment.

Regions with Heavy Snow Loads

Choosing 2×4 lumber for the metal roof is highly advisable in areas prone to heavy snowfall. Snow accumulation can exert significant downward pressure on the roof structure, requiring robust support to prevent damage or collapse.

The larger cross-sectional area of 2×4 lumber provides enhanced strength, ensuring the roof can withstand the added weight of snow loads and maintain its structural integrity.

High-Wind Areas

For regions with frequent high-wind events, such as coastal or hurricane-prone areas, the use of 2×4 lumber is crucial. Metal roofs in these locations must withstand powerful gusts and wind uplift forces.

The larger dimensions of 2×4 lumber offer increased rigidity and resistance against wind-induced stresses, reducing the risk of roof failure or damage.

Wide Rafter or Purlin Spacing

If you prefer wider spacing between rafters or purlins in your metal roof assembly, 2×4 lumber is recommended.

The greater stiffness and load-carrying capacity of 2×4 lumber allow for longer spans between supports without compromising structural stability.

This flexibility in spacing can facilitate faster installation and potentially reduce overall construction costs.

How to Install a Metal Roof? DIY Guide

Installing a metal roof requires careful planning, precise measurements, and attention to detail.

In this step-by-step guide, I will walk you through the process of installing a metal roof, ensuring a durable and weather-resistant roofing system for your building.

Step 1: Prepare the Roof

  • Remove any debris, leaves, or loose materials from the roof surface. Use a broom or a blower to clean the area thoroughly.
  • Pay attention to valleys, gutters, and areas around roof penetrations to ensure they are clear and free from obstructions.
  • Carefully examine the roof deck for any signs of damage, such as rot, decay, or weakened areas.
  • Replace or repair any compromised sections to ensure a solid and stable base for the metal roof.
  • Cut out and remove any damaged or decayed wood and replace it with new, structurally sound material.
  • Secure the new wood to the roof deck using appropriate nails or screws, ensuring a secure and stable surface for the metal roof installation.

Required Tools

  • Broom or blower
  • Hammer or screwdriver
  • Nails or screws

Step 2: Take Measurements and Order Materials

  • Use a tape measure to measure the roof’s dimensions accurately.
  • Measure the length and width of each roof section separately, including any dormers, extensions, or additional structures.
  • Consider any unique features, such as valleys or skylight domes, that may require special attention during installation.
  • Order the necessary metal roofing panels, shingles, purlins, lumbers, ridge caps, flashing, screws, closures, and any additional accessories required for your specific project.

Required Tools

  • Tape measure

Step 3: Install the Purlin System

  • Use a chalk line or a straight edge to mark the positions of the purlins on the roof deck.
  • Start at the eaves and work your way up, ensuring consistent spacing and alignment throughout the roof surface.
  • Cut the 1×4 or 2×4 lumber to the appropriate lengths for each purlin, considering the marked positions and layout.
  • Position the first purlin at the roof’s eaves, aligning it with the marked position.
  • Securely attach the purlin to the roof deck using appropriate fasteners, such as screws or nails.
  • Continue installing the remaining purlins, placing them every 24 to 36 inches.
  • Install additional bracing or bridging between the purlins to enhance the structural stability of the system.
  • Use a level or a string line to ensure consistent alignment throughout the roof surface.
  • Check for any loose fasteners and tighten them as necessary to maintain structural integrity.

Required Tools

  • Chalk line or straight edge
  • Saw
  • Drill or hammer
  • Screws or nails
  • Level or string line

Step 4: Install the Underlayment

  • Choose an asphalt-saturated felt or synthetic underlayment material based on the specific requirements of your metal roofing system and local building codes.
  • Unroll the underlayment material and cut it into manageable lengths if needed.
  • Ensure you have enough underlayment to cover the entire roof surface.
  • Begin at one corner of the roof, typically the eaves, and position the first row of underlayment parallel to the edge.
  • Allow for a slight overhang at the eaves to ensure proper water drainage.
  • Lay subsequent rows of underlayment, working your way up the roof parallel to the eaves.
  • Overlap each row of underlayment by a few inches.
  • This overlapping method helps ensure proper water shedding and prevents water infiltration.
  • Use roofing nails or staples to secure the underlayment to the roof deck and purlin system.
  • Place the fasteners at recommended intervals along the edges and field of the underlayment.
  • Apply consistent tension to the underlayment as you install it, ensuring a smooth and wrinkle-free surface.
  • Cut openings in the underlayment to accommodate roof penetrations such as chimneys, vents, or skylights.
  • Install appropriate flashing or sealant around these penetrations to ensure a watertight seal.
  • Verify that there are no gaps, tears, or areas where the underlayment is improperly installed.

Required Tools

  • Asphalt-saturated felt or synthetic underlayment material
  • Utility knife or scissors
  • Roofing nails or staples

Step 5: Install the Metal Panels

  • Position the first metal panel at the starting edge of the roof, typically the eaves.
  • Ensure the panel aligns properly with the roof’s edge and overlaps the underlayment.
  • Use self-tapping screws or rivets specifically designed for metal roofing to secure the panel to the purlins.
  • Place fasteners at predetermined intervals along the panel’s ridges or seams.
  • Ensure the fasteners penetrate both the metal panel and the purlins, creating a secure connection.
  • Install the next panel, aligning it with the first panel and overlapping the panels as required.
  • Typically, metal panels have specific overlap requirements, such as 6 to 12 inches, to ensure proper water shedding and structural integrity.
  • Secure the second panel to the purlins using the same method as the first panel, maintaining the spacing for fasteners.
  • Repeat the process of positioning, fastening, and overlapping the panels, moving horizontally along the roof surface.
  • Ensure each panel is securely attached to the purlins and properly aligned with the previous panel.
  • Trim panels as necessary to fit around roof penetrations or edges using tin snips.
  • Complete the metal panel installation by installing ridge caps along the roof peak.

Required Tools

  • Metal roofing panels
  • Self-tapping screws or rivets
  • Screw gun or rivet gun
  • Tin snips

Step 6: Install the Flashing

  • Install edge flashing along the perimeter edges of the metal panels, such as the eaves and rakes, to provide a watertight seal.
  • Ensure the flashing extends beyond the edge of the metal panels and overlaps the underlayment or other roofing components as necessary.
  • Attach the edge flashing securely to the roof deck using appropriate fasteners.
  • Install flashing around roof penetrations, including chimneys, vents, skylights, and any other openings on the roof.
  • Cut the flashing material to the required size and shape to fit around the penetration.
  • Apply a suitable roofing sealant or adhesive to the backside of the flashing.
  • Position the flashing around the penetration, ensuring it covers the joint between the metal panel and the penetration.
  • Secure the flashing in place using appropriate fasteners or adhesives, ensuring a tight and secure fit.
  • Install step flashing or counter flashing around chimneys to prevent water infiltration at the chimney joints.
  • Attach step flashing pieces vertically between the metal panels and the chimney, interlocking them with each metal panel.
  • Install a continuous piece of counter flashing over the step flashing, securely sealing the joint between the chimney and the metal panels.
  • Install flashing around skylights and vents, following the specific instructions provided by the skylight or vent manufacturer.
  • Ensure the flashing is properly integrated with the metal panels and the skylight or vent, providing a watertight seal.

Required Tools

  • Edge flashing material
  • Roofing sealant or adhesive
  • Fasteners

Step 7: Conduct a Final Inspection

  • Inspect the installed metal roof, purlin system, underlayment, metal panels, and flashing for any visible defects, loose fasteners, or gaps.
  • Verify that all flashing, trim, and accessories are properly installed and securely in place.
  • Check for proper drainage, ensuring that water flows away from the roof as intended.

By following these step-by-step instructions, you can successfully install a metal roof with a purlin system, underlayment, metal panels, and flashing.

What is the Spacing of Furring Strips For Metal Roofs?

Furring strips, also known as battens, provide a supportive framework that helps distribute the weight of the metal panels and create a level surface. Furring strips are usually spaced somewhere between 12 inches to 24 inches apart.

For corrugated metal roofing, spacing the strips up to 24 inches apart is generally acceptable.

On the other hand, standing seam metal roofing typically requires strips to be spaced up to 18 inches apart.

While it may be tempting to reduce costs by using fewer furring strips or even omitting them altogether, this is generally not advisable.

Particularly if you have already installed shingles, using furring strips becomes even more critical.

Without them, your roof may experience moisture issues and appear uneven over time, as metal panels tend to conform to the shape of the underlying shingles.

The slope or pitch of your roof also influences the spacing of the furring strips. The steeper the slope, the further apart you can space the strips.

Before you begin the installation process, it’s crucial to determine your roof’s pitch. For low slopes with a pitch of 2/12 or less, spacing the strips up to 16 inches apart is recommended.

In contrast, for steep slopes with a pitch greater than 2/12, spacing the strips up to 24 inches apart is typically suitable.

While furring strips add to the cost of a metal roof, they are typically a worthwhile investment. Their presence helps prevent issues that can prematurely age your roof, ensuring its longevity and durability.

Bottom Line

Choosing the right lumber for your metal roof is a crucial decision that requires careful consideration of factors such as roof size, load-bearing requirements, budget constraints, and local building codes.

While 2×4 lumber offers greater strength and load-bearing capacity, there are situations where 1×4 lumber can be a practical and cost-effective choice.

By making an informed decision based on the factors discussed in this guide, you can select the most suitable lumber for your metal roof, ensuring a structurally sound, long-lasting, and cost-effective roofing solution.


What is the best wood to use under a metal roof?

When it comes to selecting the ideal wood for supporting a metal roof, it’s crucial to steer clear of pressure-treated wood due to its harmful interaction with metal.

The chemical reactions between the preservatives found in pressure-treated wood and dissimilar metals like copper can lead to rust formation, compromising the roof’s structural integrity.

To ensure a reliable and long-lasting installation, you should opt for untreated pine or spruce stringers as they securely attach the metal panels.

How thick should a steel roof be?

The most commonly used gauges for metal roofing are 29, 26, 24, and 22 gauge. For low-end agricultural projects, 26 gauge or even 29 gauge are sufficient.

However, for high-quality residential applications, such as a home with a standing seam roof, you should go for the thicker 24 gauge metal roofing.

What is the best thing to put under a metal roof?

Asphalt felt or tar paper stands out as the most common and widely used option for steeper-sloped metal roofs.

This versatile material provides several benefits that contribute to the overall performance and longevity of the roof.

Felt underlayment acts as a protective barrier, shielding the roof deck from moisture infiltration and helping to prevent leaks.

It also provides an additional layer of insulation, reducing heat transfer and enhancing energy efficiency.

The asphalt-soaked felt is easy to install and offers a cost-effective solution for metal roof installations.

Its flexibility and ability to conform to the roof’s contours make it an ideal choice for ensuring a secure and watertight seal.