Furring strips for siding are a practical solution for improving moisture management, venting behind siding, and creating a uniform surface for installation. This guide covers when to use furring strips, how to select materials and sizes, installation steps, and maintenance tips. Proper use helps prevent moisture damage, reduce warping, and extend the life of exterior siding systems.
What Are Furring Strips And Why They Matter
Furring strips are narrow boards or metal channels installed away from the wall to create a ventilation gap and a plumb, straight surface for siding. They elevate the siding to allow air flow behind it and provide a space for vapor diffusion. For some cladding systems, furring strips also help level irregular walls and accommodate insulation or weather barriers.
Key benefits include improved drainage, reduced moisture buildup, easier installation on uneven surfaces, and compatibility with rainscreen or ventilated siding designs. They are especially useful in retrofit projects where existing siding needs a new, stable substrate.
When To Use Furring Strips For Siding
Consider furring strips in these scenarios: exterior walls with moisture concerns, installations over existing siding or masonry where a vented cavity is beneficial, and projects requiring a level surface due to irregularities. They are also advantageous when adding insulation with a ventilated gap behind the siding or when upgrading to a rainscreen system for enhanced moisture management.
Before proceeding, verify local building codes and manufacturer guidelines for the chosen siding material to ensure compatibility and warranty considerations. In some cases, alternative methods like sheathing with a continuous air barrier or a full rainscreen may be more appropriate.
Materials And Sizing
Furring strips come in wood and metal options. Wood options include common softwoods like pine or fir, while metal options use aluminum or galvanized steel channels. Wood is generally easier to work with and cost-effective; metal provides greater durability and consistent straightness in large installations.
Common dimensions range from 1×2 inches to 1×3 inches for wood, with metal furring channels offered in similar depths. The thickness and spacing depend on siding type and climate: for example, siding with heavy insulation may require wider strips or closer spacing to maintain a stable surface. Typical spacing is 16 inches on center, but this can vary by product and climate zone.
Additional considerations include fastener type and corrosion resistance. For metal furring, use corrosion-resistant fasteners rated for exterior use. For wood, pressure-treated or naturally rot-resistant species reduce decay risk when in contact with the substrate.
Preparation And Tools
Prepare the surface by cleaning loose material and inspecting for structural damage. Determine the desired vented cavity width to meet moisture and insulation goals. Gather tools such as a chalk line, tape measure, level, saw (or miter saw), drill/driver with exterior bits, and corrosion-resistant fasteners. If using metal furring, have a snips tool for trimming and appropriate drilling bits for metal.
Protect adjacent materials from dust and debris. If a moisture barrier or weather-resistive barrier is present, plan how furring strips integrate with it to avoid creating moisture traps. Mark stud locations or solid backing to ensure secure anchoring.
Installation Step-By-Step
Begin by outlining the planned vertical or horizontal orientation of the furring strips based on the siding design. Install the first course as a level reference point using shims or spacers as needed. Secure strips with exterior-grade fasteners into studs or solid backing, verifying plumb with a level at multiple points.
Maintain the targeted air gap and ensure fasteners do not protrude beyond the panel surface. If using vapor barriers or a rainscreen, attach the barrier first and then fix the furring strips, keeping the barrier intact to preserve its function. Check alignment frequently and adjust as necessary before proceeding with additional strips.
Space considerations: typically 16 inches on center for siding, but follow product specs. For heavier cladding or thicker insulation, consult manufacturer guidelines to determine optimal strip width and spacing. Once the furring frame is complete, install the siding panels as per their installation instructions, ensuring ventilation openings remain unobstructed.
Ventilation, Moisture, And Siding Compatibility
A primary reason to use furring strips is to create a ventilated cavity behind siding. Adequate airflow helps dry any moisture that penetrates the outer shell and reduces the risk of mold and rot. Ensure that the design provides continuous drainage paths at the base and at penetrations such as windows or corners.
Compatibility matters: confirm that the chosen siding, be it vinyl, fiber cement, wood, or metal, works with a vented gap. Some products require a specific cavity width or mounting method to meet warranty conditions. Installers should also consider a continuous air barrier or rainscreen system if climate conditions warrant enhanced moisture control.
Finishing And Maintenance
After siding is installed, inspect all fasteners for tightness and check for any gaps where moisture could intrude. Periodic maintenance includes inspecting caulk joints at corners and around openings, re-sealing where necessary, and checking for wood decay or metal corrosion. In coastal or high-humidity areas, schedule more frequent inspections to catch early signs of moisture intrusion.
Clean the exterior surfaces as recommended by the siding manufacturer. If paint or stain is used on wood furring strips, maintain a regular repaint or re-stain cycle to protect against weathering. For metal furring, inspect for rust and treat promptly if noticed.
Cost And Sourcing
Costs vary by material, size, and project scale. Wood furring strips are typically more economical upfront but may require maintenance over time. Metal furring strips offer durability and precision, potentially reducing labor time on larger projects. Labor costs can be significant depending on wall complexity and the need for a ventilated cavity.
When sourcing, prefer exterior-grade materials and fasteners suitable for exposure to rain, sun, and temperature swings. Check warranties on both the furring system and the siding product to ensure compatibility and coverage for the assembly as installed.
Common Mistakes And Troubleshooting
Common issues include misaligned strips, insufficient ventilation, and improper fastening that can strip threads or damage the substrate. To avoid these problems, verify plumb and level frequently during installation, ensure the vent gap is continuous, and use correct fasteners for the substrate. If warping or bowing occurs in wood furring, re-trim or replace affected strips before continuing.
In retrofit scenarios, ensure the existing wall can support the additional load and that removing old materials won’t compromise structure. If moisture issues persist after installation, reassess the barrier, cavity, and drainage pathways to identify hidden moisture sources.
Frequently Asked Questions
- What gap should furring strips create behind siding? A typical ventilated cavity ranges from 3/8 inch to 1 inch, depending on siding type and climate.
- Can furring strips be installed over painted siding? Yes, but assess adhesion of existing coatings and ensure a clean surface for the new installation.
- Are metal strips better than wood? Metal offers durability and straightness; wood is easier to work with and often cheaper, but may require more maintenance.