Cedar shingles have long been prized as an exterior cladding for their natural beauty and durability. However, even the finest cedar can fail prematurely if moisture gets trapped behind it. That is where a properly designed rainscreen ventilation system makes all the difference. By creating an air space between the shingles and the wall sheathing, you allow the back side of the cedar to dry as effectively as the front. This article covers the complete process of installing cedar shingles over a rainscreen with an integrated air intake system, from materials selection through final installation.
Understanding Rainscreen Technology for Cedar Shingles
What Is a Rainscreen and Why It Matters
A rainscreen is a ventilated drainage plane behind exterior cladding. It consists of a small air gap, typically 1/4 to 1 inch wide, separating the siding from the weather-resistant barrier. This gap serves two critical functions: it allows moisture that penetrates the siding to drain downward by gravity rather than soaking into the wall assembly, and it enables airflow behind the cladding to promote drying through evaporation. For cedar shingles, which are naturally porous and absorb moisture from rain and humidity, this back-ventilation is essential for preventing rot, cupping, and fungal growth.
Research shows that wall assemblies with a ventilated rainscreen outperform those with siding applied directly to sheathing. Air movement behind the cladding reduces wood moisture content by 20 to 30 percent compared to unventilated assemblies, dramatically extending siding service life. Combined with proper flashing at the base and top of the wall, a rainscreen creates a durable enclosure lasting decades.
How Cedar Shingles Benefit from Back-Venting
Cedar shingles present a unique case for rainscreen design. Shingles are installed with overlapping courses that create many small ledges where water can be held by surface tension. In a direct-application scenario, moisture that works between overlapping shingles has no escape path except the front face or migration into the sheathing. A rainscreen changes this.
The air space behind the shingles allows moisture that soaks into the front to dry to the back side as well. This two-sided drying is crucial in climates with frequent rain, high humidity, or freeze-thaw cycles. Cedar shingles over a rainscreen can last 40 to 60 years, while those applied directly against housewrap often need replacement after 20 to 30 years due to hidden rot at the exposure line and nail heads.
Materials and Components for a Vented Cedar Shingle Wall
Choosing the Right Rainscreen Mat
The most common method for creating a rainscreen gap behind cedar shingles is a three-dimensional plastic mesh mat. Products like Benjamin Obdyke Home Slicker use a matrix of entangled polymer filaments that create an approximately 1/4-inch drainage and ventilation space. The mat is lightweight, easy to handle, and rolls out horizontally or vertically across the sheathing. It is held temporarily with cap nails, and the eventual nailing of the shingles secures it permanently.
In regions with heavy rainfall, a thicker mat providing a 1/2-inch or 3/4-inch gap may be preferable for increased drainage. Some products incorporate a built-in housewrap layer, combining drainage and weather protection. Whichever product you choose, verify it is compatible with cedar shingles and approved for vertical wall applications.
Air Intake Systems at the Wall Base
The air intake at the bottom of the wall is the most critical detail in a vented rainscreen assembly. Without a properly sized and protected intake, the ventilation cavity cannot function. An effective solution is a corrugated plastic vent strip such as DCI Products CedarVent Plus. These strips have a non-woven mesh screen along one edge that keeps insects out while letting air flow freely into the cavity behind the shingles.
Vent strips come in depths from 1/2 to 1 inch, matching the rainscreen gap. The strip installs at the base behind the skirt board with the mesh screen oriented downward. Combined with pressure-treated lumber spacers that support the skirt board off the wall, the intake system creates a continuous air pathway from the exterior into the rainscreen cavity. Spacers should be set at 24 inches on center over wall studs, with tops cut at a 15-degree angle to support the drip cap flashing.
Cap Flashing and Top Outlet Details
Just as air must enter at the bottom, it must exit at the top. Properly designed cap flashing sheds water from the wall while creating an opening for warm, moist air to escape. The flashing wall leg should be spaced off the wall so air flows freely between intake and outlet. A thin strip of vent material behind the flashing wall leg prevents it from bending inward and closing off the vent space, while supporting the top course of shingles.
Behind the frieze board at the top of the wall, an air outlet is created by terminating the rainscreen mesh below the flashing. The outlet should be protected with bug screen and sized to match or exceed the net free area of the intake. A system with both intake and outlet creates a natural convection loop: sunlight heats the siding, air inside the cavity warms and rises, drawing cooler air in at the bottom and flushing moisture-laden air out the top.
Step-by-Step Installation Process
Preparing the Wall and Installing the Skirt Board
Begin by ensuring the wall sheathing is clean and dry. Install the weather-resistant barrier according to manufacturer instructions, lapping all seams and integrating with window and door flashings. Mark stud locations so skirt board spacers align with them.
The skirt board, made from durable material like Boral or pressure-treated lumber, serves as the starting point for shingle installation. Cut 7/8-inch rips of pressure-treated lumber as spacers, attaching them vertically at each stud location. Each spacer extends slightly above the skirt board top with a 15-degree angle cut to match the drip cap flashing slope. Install the skirt board against the spacers, level and aligned with building corners, then install the drip cap flashing.
Setting Up the Air Intake
With the skirt board and flashing in place, cut vent strips to fit between the spacers. Use 1-inch-depth strips so the skirt board presses tight against them. Press each strip into place with the mesh screen oriented downward, corrugated channels running vertically for unobstructed airflow into the cavity above.
Install a 3/16-inch strip of vent material behind the flashing wall leg. This prevents the flashing from bending in and closing off the vent space while providing a stable bearing surface for the bottom shingle course. The combination creates a robust intake assembly that remains functional for the building’s life.
Installing the Rainscreen Mat and Cedar Shingles
Roll out the rainscreen mat horizontally across the wall, starting at the bottom. Tack it temporarily with cap nails near the top edge, overlapping horizontal seams by at least 2 inches. Tuck the bottom edge behind the drip cap flashing.
Begin installing cedar shingles from the bottom course, extending below the skirt board for a proper drip edge. Follow these fastening best practices:
- Use hot-dipped galvanized or stainless steel ring-shank nails to prevent corrosion and pull-out.
- Drive nails flush with the shingle surface without overdriving, which can split the cedar.
- Maintain consistent exposure: 4 to 6 inches for 16-inch shingles, 5 to 7 inches for 18-inch shingles.
- Stagger butt joints so no two adjacent courses share a joint within 1.5 inches.
- Leave a 1/8-inch gap between adjacent shingles for expansion during wet weather.
- Each shingle gets two nails, 3/4 inch from edges and 1 to 2 inches above the butt line.
As each shingle is nailed, the fastener passes through the rainscreen mat and presses it firmly against the wall. After several courses, the hundreds of nails securing the shingles also hold the mat permanently. Continue installing courses up the wall, checking alignment regularly.
Installation Sequence Summary
| Step | Task | Key Detail |
|---|---|---|
| 1 | Install WRB and flashings | Lap seams, integrate with windows and doors |
| 2 | Mount skirt board spacers | 7/8 in. PT lumber at 24 in. oc, angled tops |
| 3 | Install skirt board and drip cap | Level and flush, sloped flashing on spacers |
| 4 | Place vent strips between spacers | Mesh screen facing down, 1 in. depth |
| 5 | Install thin vent strip behind flashing | 3/16 in., supports flashing and shingles |
| 6 | Roll out rainscreen mat | Tack temporarily, overlap seams 2 in. |
| 7 | Install first shingle course | Extend below skirt board, align carefully |
| 8 | Continue shingling up the wall | Stagger joints, maintain exposure, check alignment |
| 9 | Install top outlet at frieze board | Leave open cavity, protect with bug screen |
Best Practices and Common Mistakes
Ensuring Proper Airflow Through the Cavity
The effectiveness of any rainscreen depends on maintaining an unobstructed airflow path from intake to outlet. One common mistake is failing to provide adequate intake area. The vent strip must be sized to match the cavity volume, and the mesh screen must be kept clean during construction. Cover the intake with temporary protection during ongoing work to prevent sawdust and debris from clogging the mesh.
Another frequent error is allowing the rainscreen mat to sag or compress at the wall base, restricting airflow. Use spacers slightly thicker than the mat to maintain positive pressure against the skirt board. At the top, ensure the frieze board does not block the outlet. For specialized applications, see our gable end rainscreen details guide.
Fastening Techniques for Cedar Shingles
Nails must pass through the shingle, rainscreen mat, and housewrap, penetrating at least 1 inch into framing or 3/4 inch into plywood. For shingles over a 1/4-inch mat, 1-1/2-inch nails are usually sufficient. Measure total assembly thickness on site before selecting nail lengths.
The blind nailing technique for cedar siding hides fasteners from view. Position the nail just above the overlap line of the next course so it is concealed. Do not nail through the overlap zone of the course above, which can cause splitting. Drive nails flush with the surface but avoid overdriving, which crushes wood fibers and creates a moisture intrusion path.
Maintenance and Long-Term Performance
A cedar shingle rainscreen requires minimal maintenance but periodic inspection. Check intake vents at the wall base annually and clear any debris, insect nests, or vegetation. Ensure landscaping and soil grades remain at least 6 inches below the skirt board to prevent moisture wicking and maintain clear airflow.
Inspect shingles for cupping, splitting, or fungal growth, especially on north-facing elevations. If the rainscreen functions correctly, shingles should show even weathering with no premature decay. For a broader overview of exterior cladding systems, refer to our comprehensive siding installation guide covering multiple siding types and materials.
In freeze-thaw regions, pay special attention to base flashing. Ice dams can form at the skirt board if the intake is blocked or the drip edge is inadequate. The combination of a well-designed rainscreen, quality cedar shingles, and meticulous installation produces an exterior cladding system that performs beautifully for half a century or more.