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Plank Roof Decking: A Complete Guide for Homeowners
When it comes to roofing, one of the most important but often overlooked elements is the roof deck. This is the structural base that supports shingles, underlayment, and everything else that keeps your home protected. Among the different options available, plank roof decking is a traditional choice that has been used in homes for decades. Homeowners who are repairing, replacing, or upgrading their roofs may come across the term but may not fully understand what it means, how it works, or how it compares to other decking options.
This guide will explore everything you need to know about plank decking, from its history and construction to its benefits, drawbacks, and costs.
What Is Plank Roof Decking?
Plank decking refers to a roof deck made from individual wood planks, usually 1×6 or 1×8 boards, that are nailed side by side across the roof rafters. Before the widespread use of plywood and oriented strand board (OSB), planks were the standard material for roof decking.
Characteristics of Plank Decking:
- Material: Typically solid wood, often pine or fir.
- Thickness: Commonly ¾ inch for strength.
- Installation: Boards are laid perpendicular to the rafters.
- Spacing: In older homes, planks were sometimes spaced apart to allow for wood shingles to breathe. In modern applications, they are installed tightly together.
Plank decking forms the foundation for all roofing materials. Without a strong deck, shingles or other coverings cannot perform as intended.
A Brief History of Plank Decking
For much of the 19th and early 20th centuries, plank decking was the most common method of building a roof deck. Plywood did not become popular until the mid-20th century, and OSB rose in use during the late 20th century.
Older homes built before the 1970s often have plank decking, which means that during replacement, roofers may need to decide whether to repair, replace, or cover the existing planks.
Types of Plank Roof Decking
Not all plank decking is the same. There are different variations depending on the era of construction and the materials used.
1. Straight Plank Decking
- Planks laid side by side with no gaps.
- Provides solid support for asphalt or wood shingles.
2. Skip Sheathing (Spaced Plank Decking)
- Planks installed with gaps between them.
- Commonly used for wood shake or wood shingle roofs, which require airflow underneath.
- Not suitable for asphalt shingles without modifications.
3. Diagonal Plank Decking
- Installed at a 45-degree angle to the rafters.
- Provides extra rigidity and strength.
- Seen in many older homes with high structural requirements.
Advantages of Plank Decking
There are several reasons why plank decking has remained in use for so long:
- Durability – Solid wood planks are strong and can last for decades if maintained properly.
- Structural Integrity – Diagonal plank decking provides excellent resistance to lateral forces, making roofs more stable.
- Historic Authenticity – For older homes, keeping original plank decking preserves architectural integrity.
- Moisture Control (Skip Sheathing) – Spaced planks allow air circulation for wood roofing materials.
Disadvantages of Plank Decking
Despite its strengths, plank decking has some drawbacks compared to modern plywood or OSB.
- Cost of Replacement – Individual planks are more labor-intensive to install and replace.
- Uneven Surface – Old planks may warp or shrink, making it harder to install modern shingles.
- Gaps and Cracks – Wood movement can lead to gaps where underlayment may sag.
- Incompatibility with Asphalt Shingles – Spaced sheathing is not suitable for asphalt shingles unless an additional layer of plywood or OSB is installed on top.
- Availability of Material – Quality solid wood planks are less commonly used today, which can raise costs.
How to Inspect Plank Roof Decking
If you own a home built before the 1970s, chances are your roof has plank decking. When replacing shingles, contractors will inspect the deck for:
- Rot or water damage
- Warping or sagging boards
- Gaps between planks
- Signs of insect infestation
- Overall thickness and strength
If too many boards are compromised, roofers may recommend overlaying the planks with plywood or replacing them entirely.
Repairing vs. Replacing Plank Decking
When working with older homes, homeowners have three main options:
1. Repair Damaged Planks
- Suitable if only a few boards show rot or cracks.
- Involves cutting out damaged planks and replacing them with new boards.
2. Overlay with Plywood
- A cost-effective solution for spaced sheathing or uneven boards.
- Plywood sheets are nailed directly over the existing planks, creating a smooth surface for asphalt shingles.
- Adds strength and prevents sagging.
3. Full Replacement
- Best if a large portion of planks are damaged or rotted.
- More expensive due to higher labor and material costs.
- Ensures the deck meets modern building codes.
Cost of Plank Roof Decking
The cost depends on whether you’re repairing, overlaying, or replacing.
- Repairing individual planks: $200 – $500 (minor fixes).
- Overlay with plywood: $2 – $4 per square foot.
- Full replacement with new planks: $4 – $7 per square foot.
Compared to plywood or OSB, plank decking is more expensive due to labor and material availability.
Plank Decking vs. Plywood and OSB
| Feature | Plank Decking | Plywood | OSB |
|---|---|---|---|
| Strength | High (especially diagonal) | High | Moderate–High |
| Cost | Higher | Moderate | Lower |
| Lifespan | Long with maintenance | Long | Long but less moisture resistant |
| Installation Speed | Slower | Fast | Fast |
| Compatibility | May require overlay for asphalt | Excellent | Excellent |
Building Codes and Requirements
Modern building codes often require solid sheathing (plywood or OSB) for asphalt shingles. If your home has spaced plank decking, contractors may recommend overlaying it with plywood to meet code requirements.
Some municipalities allow repairs to existing plank decking as long as it remains structurally sound, but many will not approve new construction using planks alone.
Common Problems with Old Plank Decking
- Rot from Leaks – Water damage from past roof leaks can weaken planks.
- Warping – Boards may twist or bow over decades.
- Inconsistent Board Widths – Older construction used varying sizes, making replacement tricky.
- Nail Pops – Old fasteners may loosen, creating uneven surfaces.
Best Roofing Materials for Plank Decking
- Wood Shingles/Shakes – Ideal for spaced sheathing.
- Asphalt Shingles – Require a smooth base (overlay with plywood).
- Metal Roofing – Works well if planks are solid and smooth.
- Slate or Tile – Require reinforced decking due to weight.
Longevity of Plank Decking
Well-maintained plank decking can last 50 years or more. However, its actual lifespan depends on:
- Quality of original wood
- Exposure to moisture
- Maintenance of roofing materials above it
- Proper ventilation in the attic
Environmental Considerations
Plank decking made from solid wood is biodegradable and often sourced from renewable forests in earlier eras. However, replacing planks today may involve higher environmental costs compared to engineered wood products.
When to Upgrade from Plank Decking
Homeowners should consider upgrading if:
- More than 25% of planks show rot or damage.
- They want to install asphalt shingles on spaced decking.
- They are already investing in a major roof replacement.
- Their roof structure needs reinforcement for heavy materials.
Pros and Cons Summary
Pros of Plank Decking
- Strong and durable
- Traditional look for older homes
- Excellent support in diagonal installations
- Can last decades
Cons of Plank Decking
- Higher replacement cost
- Slower installation
- May not meet modern codes without overlay
- Susceptible to warping and rot
Conclusion
The choice of decking material plays a huge role in the strength and longevity of a roof. Plank roof decking remains a hallmark of older homes and can still provide excellent durability when maintained properly. While it comes with certain challenges compared to plywood or OSB, its structural integrity and historical value make it a worthwhile option in many cases.
For homeowners considering roof replacement or repair, understanding plank decking helps make informed decisions about whether to repair, overlay, or replace. With proper care, it can continue protecting a home for generations.440-235-3124
