The installation of furring strips under siding is a practical strategy to create a level surface, improve ventilation, and accommodate insulation upgrades. This guide explains when to use furring strips, how to choose materials, and step-by-step installation tips to help homeowners and professionals achieve a durable, energy-efficient siding system. It covers moisture management, ventilation considerations, and common pitfalls to avoid, with actionable guidance for various siding types used in the United States.
Benefits Of Furring Strips Under Siding
Furring strips provide a stable, plumb mounting surface when existing wall sheathing is uneven or damaged. They create an air gap that enhances ventilation, reducing moisture buildup and prolonging siding life. The technology also allows for improved insulation coverage by providing space to add or retrofit insulation behind the siding. Additionally, furring strips help with attaching heavier or unusual siding profiles by distributing fastener loads more evenly.
- Improved ventilation reduces mold risk and rot by allowing air to circulate behind the siding.
- Level mounting surface accommodates warped or misaligned walls without extensive repair.
- Moisture control with a continuous drainage plane behind the siding lowers the chance of capillary-driven moisture reaching the sheathing.
When To Use Furring Strips
Furring strips are beneficial in several scenarios: uneven wall surfaces due to settling or rot, retrofits where additional insulation is desired without removing existing siding, and projects requiring a vented rain screen system. They are commonly used with fiber cement, wood, vinyl, and metal siding systems, especially when the exterior wall lacks a continuous, stable plane. In colder climates, furring strips paired with breathability-friendly barrier films can improve thermal performance. Always verify local building codes and manufacturer instructions before starting a project.
Materials For Furring Strips
Choice of material affects durability, cost, and compatibility with siding. Common options include:
- Wood strips such as pine or poplar offer easy handling and a familiar install process but require treatment against decay in moist environments.
- Pressure-treated lumber provides enhanced rot resistance for exterior use but may warp if not properly acclimated.
- Metal furring (stainless or aluminum) delivers high dimensional stability and corrosion resistance for challenging climates but can require specialized fasteners.
- Composite or PVC strips resist moisture and insects, though they can be more expensive and may require specific fasteners.
Spacing between strips is typically 16 inches on center in standard wall assemblies, but higher loads or thicker insulation may call for closer spacing. A continuous moisture barrier or drainage plane behind the strips is recommended to manage water intrusion. Ensure compatibility with siding type and fasteners to prevent damage or warranty voids.
Installation Steps
The following steps outline a practical approach to installing furring strips under siding. Adapt the sequence to local conditions and manufacturer guidelines.
- Assess and prepare the wall — Inspect for rot, mold, or structural damage. Repair sheathing and replace damaged sections before mounting furring strips. Clear debris and ensure the wall surface is clean and dry.
- Choose height and layout — Determine the start height to align with door and window openings and ensure the top of the furring lines up with the desired siding plane. Mark stud lines or attachment points.
- Install a drainage or moisture barrier — Apply a breathable barrier or rain screen material over the sheathing to promote drainage and airflow behind the siding. Ensure overlaps and fastener access points comply with manufacturer specs.
- Cut and acclimate strips — Cut strips to length with a square cut and allow for acclimation in the installation environment to minimize warping.
- Attach furring strips — Secure strips to the wall framing using corrosion-resistant fasteners appropriate for the substrate. Maintain consistent spacing and plumbness using a level. Fasten through sheathing into studs at recommended intervals.
- Check alignment and level — Verify the first run is level, then consistently align subsequent strips to prevent ripple in the siding plane. Adjust as needed before final fastening.
- Install insulation (if applicable) — If adding insulation behind the siding, place insulation between furring strips or in the cavity while ensuring ventilation paths are not blocked. Seal edges to minimize drafts.
- Install siding over the furring — Follow the siding manufacturer’s recommendations for fastener type, spacing, and edge clearance. Ensure a continuous air gap and venting path behind the siding for moisture management.
Common Mistakes And Troubleshooting
Avoid common missteps that can compromise performance. Poorly spaced strips can create visible bumps or bowing in the siding, while improper moisture management may lead to rot or mildew behind the panels. Use corrosion-resistant fasteners compatible with both the furring material and the siding. Ensure door and window rough openings remain square to prevent gaps at transitions. If warping occurs, replace affected strips and re-check the acclimation period before reinstalling.
- Inadequate ventilation blocks airflow; consider additional drainage gaps or vented screens.
- Inconsistent alignment causes an uneven siding surface; use a laser level or long straightedge for accuracy.
- Wrong fasteners reduce holding power or cause staining; match fastener type to substrate and climate.
- Moisture trapping behind non-breathable barriers; always use breathable or drainage-enabled assemblies.
Maintenance And Longevity
Regular inspection helps extend the life of a siding system with furring strips. Check for signs of moisture intrusion, rot, or insect damage at least once a year, with additional checks after heavy rainfall or storms. Replace any damaged strips promptly and reseal edges where necessary. If insulation is added, confirm there are no gaps and that ventilation remains open. Keep fasteners tight and confirm that siding panels still align correctly to prevent moisture intrusion.
Practical Quick Reference
- Key purpose — create a stable, ventilated plane for siding installation.
- Best suits — uneven walls, retrofit insulation, vented rain-screen assemblies.
- Materials — wood, pressure-treated wood, metal, or composite/fiber materials; choose based on climate and siding type.
- Installation focus — image-level alignment, proper moisture barriers, and compatible fasteners.
With careful planning, material selection, and precise installation, furring strips under siding can improve installation quality, energy performance, and long-term durability. This approach aligns with common US construction practices and supports a wide range of siding materials, ensuring a robust exterior that handles moisture and temperature fluctuations effectively.