Upgrading Historic Missoula Roofs Through the Decades: What 1950s and 1970s Homes Need to Meet Today's Standards
Missoula's historic neighborhoods, such as the University District, Rose Park, and Lewis & Clark, are defined by their unique architectural character and enduring charm.
However, owners of these classic homes often face unexpected challenges during reroofing projects, as original roof designs frequently predate modern structural and energy-efficiency standards. Navigating these requirements involves understanding how past construction methods, such as skip decking or limited attic ventilation, interact with contemporary roofing materials like architectural asphalt shingles.
Whether you are wondering if asphalt shingles can be installed over existing skip decking, seeking solutions for converting traditional cedar shake roofs, or trying to prevent persistent ice dams during harsh Montana winters, these concerns highlight the complexity of updating older homes. Successfully modernizing an older roof requires more than a simple replacement; it necessitates a comprehensive assessment of the roof’s underlying structure and ventilation system to ensure long-term performance, safety, and compliance with current building codes.
Many homes built in the 1950s and 1970s require structural upgrades before a modern roofing system can be installed. Older roof decks, outdated ventilation, and changing building codes all play a role in ensuring a replacement roof performs safely and efficiently during Missoula's snowy winters.
This guide explains the differences between mid-century roofing systems, why reroofing older homes often involves more than replacing shingles, and how Rhino Roofing helps homeowners update historic roofs to today's standards.
How Roofing Changed Between 1950s and 1970s Missoula Homes
Not all older homes were built the same.
Construction methods changed significantly between the 1950s and the 1970s, which means roofing projects often vary depending on the home's age.
1950s Homes: The Cedar Shake Era
Many homes built throughout Missoula during the 1950s originally featured wood shingles or cedar shake roofs.
Unlike today's roofing systems, cedar shakes required continuous airflow beneath the roofing material to help moisture escape and extend the roof's lifespan.
To accomplish this, builders commonly installed skip decking, sometimes called spaced sheathing.
Instead of using solid plywood, the roof consisted of horizontal 1x4 or 1x6 boards installed with gaps between them.
This open design allowed cedar shakes to breathe naturally while supporting the roofing material.
At the time, it was considered standard construction.
1970s Homes: The Early Plywood Transition
By the 1970s, many new homes were being built with solid plywood or early OSB roof decking.
Although this represented an improvement in structural support, these homes were constructed before many of today's energy-efficiency requirements.
Common issues include:
Limited attic ventilation
Small soffit intake vents
Shallow rafter cavities
Insufficient insulation by today's standards
While these roofs often have solid decking, many still benefit from ventilation upgrades during reroofing projects.
Why Skip Decking Creates Challenges During Roof Replacement
One of the biggest surprises homeowners encounter is discovering skip decking beneath an aging cedar shake roof.
Although skip decking worked well for wood roofing materials, it isn't designed for modern asphalt shingles.
Architectural shingles require a continuous, solid roof deck that allows every roofing nail to be properly supported.
Current residential building standards recognize the importance of a structurally sound roof deck before installing modern roofing materials. Guidance published by the International Code Council (ICC), which develops widely adopted building codes, emphasizes proper roof sheathing as part of a complete roofing assembly.
Attempting to install asphalt shingles directly over spaced decking can lead to poor fastener holding strength, reduced wind resistance, and roofing systems that fail to meet current construction requirements.
How Rhino Roofing Brings Older Roofs Up to Modern Standards
When reroofing older Missoula homes, simply removing the old shingles is often only the beginning.
If Rhino Roofing discovers skip decking beneath the existing roof, the team first evaluates the structural condition of the framing and decking before installing new roofing materials.
To create a proper foundation for architectural shingles, crews typically install a new layer of structural CDX plywood or OSB sheathing over the existing spaced boards. This process creates the continuous nailing surface required for today's roofing systems.
The APA – The Engineered Wood Association provides technical guidance on structural roof sheathing and the proper use of plywood and OSB in residential construction, helping ensure roofing systems perform as intended.
Once the new sheathing is installed, the roofing system can be built using modern underlayment, flashing, ice protection, and architectural shingles.
Why Older Homes Are More Likely to Develop Ice Dams
Many homeowners assume ice dams happen because of heavy snowfall alone. In reality, attic ventilation is often the bigger issue.
Older cedar shake roofs naturally allowed heat and moisture to escape through gaps in the skip decking.
Problems arise when homeowners replace those roofs with modern materials but don't upgrade the attic ventilation.
Without adequate airflow:
Warm air becomes trapped inside the attic.
Snow melts unevenly across the roof.
Meltwater flows toward colder eaves.
Water refreezes along the roof edge.
Ice dams begin to form.
These ice dams can force water beneath shingles and into ceilings, walls, and insulation.
Neighborhoods with mature homes, such as Rose Park, often experience these problems because many original ventilation systems no longer meet modern roofing standards.
Modern Ventilation Makes a Significant Difference
Today's roofing systems are designed to maintain balanced attic ventilation.
Rather than allowing heat to build up, fresh air enters through soffit or intake vents while warmer air exits through a continuous ridge vent installed at the roof peak.
Building codes commonly use ventilation ratios to determine the amount of attic airflow needed based on the home's design.
By creating a continuous flow of air through the attic, modern ventilation systems help:
Reduce attic temperatures during summer
Minimize moisture buildup
Lower the risk of ice dams
Improve insulation performance
Extend roof lifespan
Proper ventilation doesn't just protect the roof; it also helps improve the home's overall energy efficiency.
Understanding Missoula County Reroof Requirements
Replacing a roof involves more than selecting materials.
Many reroof projects require permits and inspections to verify that construction meets current standards.
The Missoula County Building Inspection Division provides guidance on residential building permits and inspection requirements. Depending on the scope of work, inspectors may review elements such as the roof deck, underlayment, flashing, drip edge installation, and ice barrier placement before the roofing system is completed. For homes located in areas susceptible to ice dams, modern roofing assemblies often include an ice and water barrier that extends beyond the exterior wall line to provide additional moisture protection.
Homeowners should always verify current permit requirements and applicable fees with the local building department before beginning a reroof project, as regulations may change over time.
Modern Fastener Requirements
Roofing installation practices have also changed over the years.
Many older roofs were installed using staples, but modern roofing systems typically require approved roofing nails installed according to the manufacturer's specifications and applicable building codes.
Using the correct fasteners helps improve wind resistance, secure shingles more effectively, and support warranty requirements for many roofing products.
Professional roofing contractors stay current with manufacturer installation guidelines to help ensure the finished roof complies with modern standards.
How Rhino Roofing Restores Older Missoula Homes
Every historic home has its own construction history.
Before beginning a reroof project, Rhino Roofing carefully evaluates the existing roof structure, decking, ventilation, insulation, and overall condition to identify any upgrades needed before installing new materials.
Whether replacing an aging cedar shake roof, upgrading skip decking to solid sheathing, or improving attic ventilation, the goal is to create a roofing system that performs reliably through Missoula's snow, wind, and changing seasons while meeting today's construction standards.
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A Balanced Perspective
Not every older roof requires complete structural upgrades.
Some 1970s homes already have solid roof decking and only need ventilation improvements or minor repairs before a new roofing system is installed.
However, homes with original cedar shake roofs or skip decking often require additional work to meet modern installation standards. Although these upgrades increase the initial project cost, they help improve durability, energy efficiency, and long-term roof performance.
Frequently Asked Questions
Can asphalt shingles be installed over skip decking?
Generally, no. Modern architectural shingles require a continuous, solid roof deck such as plywood or OSB to provide proper fastener support and meet current installation standards.
What is skip decking?
Skip decking, also called spaced sheathing, is a roof deck made from wood boards installed with gaps between them. It was commonly used beneath cedar shake roofs in homes built during the mid-1900s.
Why do older Missoula homes develop ice dams?
Many older homes have inadequate attic ventilation and insulation. Warm attic air melts roof snow, which refreezes at the eaves and creates ice dams.
Does every older home need new roof sheathing?
Not always. Homes with existing solid plywood or OSB decking may not require re-sheathing if the deck remains structurally sound. A professional roof inspection can determine what's needed.
Why is proper attic ventilation important during a reroof?
Balanced ventilation helps regulate attic temperature, reduce moisture buildup, improve energy efficiency, and minimize the risk of ice dams during Missoula winters.
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