Best Underlayment Options for Roofing
Selecting the right underlayment is a critical decision when planning any roofing project. Underlayment creates a secondary layer of weather protection, helps prevent leaks, and can enhance the durability of the roof itself. But with so many types of underlayments on the market, how do you determine what is the best product for your specific roofing needs?
This comprehensive guide will examine the most popular underlayment options, Key factors to consider when selecting underlayments, installation best practices, and tips for proper underlayment maintenance.
What is Roofing Underlayment?
Roofing underlayment is a layer of water-resistant or waterproof material installed directly on top of the roof deck, underneath the primary roof covering (shingles, metal roofing, etc.). It serves several vital functions:
- Forms a secondary barrier against rain, snow melt, and wind-driven moisture
- Helps prevent water damage inside the home if the main roofing layer is compromised
- Creates a slip-resistant surface for roofers to walk safely during installation
- Shields vulnerable areas like valleys and eaves from excess water
- Helps smooth out small imperfections or protrusions on the roof deck
Common Types of Underlayments
There are several major categories of underlayment material for residential and commercial roofing projects:
Asphalt-Saturated Felt
Asphalt-saturated felt, often referred to as tar paper, is the traditional underlayment used in roofing for decades. It is an organic felt material, reinforced with fiberglass strands, then saturated with asphalt to make it water resistant.
Asphalt felt is inexpensive, readily available, and easy to install using standard roofing nails. It provides decent water resistance, but lacks advanced moisture protection capabilities of modern synthetic underlayments. Over time, felt is also prone to cracking and deterioration.
Synthetic Felt Underlayments
Synthetic felt underlayments offer benefits over traditional organic asphalt felt. They are manufactured from recycled fibers, polymers, and woven scrim reinforcements to create a high-strength, tear resistant barrier.
Popular brands like Tyvek and Typar are lightweight with increased weathering properties. However, synthetics usually have a higher upfront cost than standard felt.
Self-Adhering Underlayments
Self-adhering underlayments feature a membrane laminated with a butyl or rubberized asphalt adhesive backing. This allows the material to stick directly to the roof deck without requiring fasteners.
Major advantages of peel-and-stick underlayment are their waterproof barrier and ease of installation around trouble areas. On the downside, they are more expensive and lose adhesion properties when exposed to high temperatures.
Breathable Underlayments
Breathable roof underlayments have a porous structure that allows for moisture vapor to escape from the attic area. This helps prevent condensation buildup and mold growth on attic framing.
Common breathable underlayment materials are synthetic roofing underlayments or housewraps like Tyvek HomeWrap. While breathability is beneficial, these products generally provide less watertightness than other coverings.
Rubberized Asphalt Underlayment
Rubberized asphalt underlayments incorporate a strong, flexible polymer material with an asphalt adhesive backing. Top products like Grace Ice & Water Shield are self-sealing around roofing nails and withstand ponded water.
Rubberized asphalt is extremely effective for leak protection and waterproofing. But the enhanced performance comes at a steep price, making it one of the more expensive underlayment options.
How to Choose the Best Underlayment
With the wide variety of underlayment products available, choosing the right one involves weighing several factors:
Climate Conditions
Your regional climate is a major factor determining proper underlayment selection. In cold, wet, and snowy regions, ice barrier underlayments provide critical protection against ice dams and wind-driven moisture. In hot and dry areas, breathable products help reduce attic humidity.
Roof Pitch and Type
Steeper sloped roofs generally require standard asphalt felt or synthetic underlayments, while lower sloped and flat roofs demand advanced self-adhering or rubberized membranes.
Your roofing material type (shingles, metal, tile, etc.) must also be compatible contact with underlayment adhesives and prevent potential chemical interactions.
Installation Considerations
Factor in underlayment width (common sizes are 36" or 48") for sufficient coverage per piece and easier application. Also consider additional ventilation needs for breathable housewrap barriers.
Budget
Higher performance underlayments provide better leak protection but cost significantly more than basic felt or synthetics. Prioritize vulnerable areas like eaves, valleys, and skylights for upgraded coverage.
How to Install Underlayments
Proper underlayment installation practices are crucial to achieve full weather protection capabilities and prevent leaks:
Ensure Proper Overlaps
Follow manufacturer specifications for correct overlap distances between courses. This keeps water from seeping underneath into vulnerable areas.
Seal Penetrations and Junctions
Carefully detail and seal underlayments around roof features like skylights, vents, and chimneys using manufacturer approved tapes.
Follow All Instructions
Adhere strictly to underlayment installation instructions for fastening methods, slope limitations, and contacting adhesives with other building materials.
Underlayment Maintenance Tips
It is wise to inspect underlayments when re-roofing or after major storms. Look for:
- Blisters, cracks, tears, or deterioration
- Areas of insufficient overlap or gaps
- Loss of granular surface coating
- Broken or popped fasteners
Make necessary repairs by re-attaching loose sections or installing new underlayment as needed before adding new roof covering.
Cost Comparison of Top Underlayments
Underlayment prices can vary widely depending on material, size, and performance qualities:
Asphalt Felt Rolls
- 36" x 144' Double Coverage Roll - $100 to $200 range
- 48" x 250' Commercial Roll - Around $850 per roll
Peel-And-Stick Membranes
- 36" x 75' Roll - $200 to $350 range
Synthetic Water Barriers
- Tyvek Pro Plus 48" x 200' Roll - $250 to $400 range
Common Underlayment Problems
Faulty underlayment installation or selection can lead to numerous roofing issues down the road:
Wrinkling
Excessive wrinkling prevents proper bonding to the roof deck and causes gaps for water intrusion. Ensure underlayment lays smooth and flat.
Insufficient Fastening
Underlayments require proper fastener spacing and overlap distances. Inadequate attachment allows blow-off and leakage around fastener holes.
Tears During Roofing
Low tear strength underlayment can rip from foot traffic during installation. Choose reinforced, high strength synthetic barriers.
Alternative Underlayments to Consider
Beyond the common options, contractors may recommend alternative underlayment products for specialized cases:
Polyiso Foam Underlayment
Polyiso foam provides insulation and waterproofing in one self-adhered layer but requires careful installation to avoid moisture risks.
Modified Bitumen Sheets
Modified bitumen combines flexible SBS polymer with asphalt for increased durability as a commercial roofing underlayment.
Installing the optimal underlayment for your roofing project involves balancing weather protection performance, climate conditions, roof type, and budget. Top-rated asphalt felts provide affordable coverage, while advanced synthetics and rubberized membranes offer premium leak protection.
Following manufacturer guidelines for underlayment installation, overlap, detailed flashing, and fastening ensures the product performs as intended. Regular underlayment inspection and timely replacement under new roof coverings also maintains critical secondary protection against wind, rain, snow melt, and moisture over your roof's service life.