Introduction: The Hidden Layer

Underlayment is the waterproof barrier between your roof deck and shingles. It's your last line of defense against leaks. Two main types exist: traditional felt paper and modern synthetic. This guide compares them head-to-head.

QUICK COMPARISON TABLE

SYNTHETIC UNDERLAYMENT

What is Synthetic Underlayment?

Materials:

• Base: Woven or non-woven polypropylene/polyethylene
• Coating: Polymer coating for waterproofing
• Reinforcement: Fiberglass scrim (some brands)

Popular Brands:

• GAF: FeltBuster, Deck-Armor
• IKO: RoofGard, Stormtite
• Owens Corning: ProArmor, RhinoRoof
• CertainTeed: DiamondDeck, RoofRunner

Advantages of Synthetic Underlayment

1. Superior Tear Strength

• Won't tear: Can walk on it without damage
• Wind resistant: Won't blow off before shingles installed
• Installation: Easier to install (doesn't rip)

2. Better Water Resistance

• Non-absorbent: Doesn't absorb water (felt does)
• Stays flat: Doesn't wrinkle when wet (felt does)
• Better protection: Superior waterproofing

3. UV Resistance

• Exposure time: 30-180 days before shingles (brand dependent)
• vs felt: Felt degrades in 2-7 days
• Benefit: Protects roof if project delayed

4. Lightweight

• Weight: 50-70% lighter than felt
• Handling: Easier to carry, install
• Labor: Faster installation

5. Longer Lifespan

• Lifespan: 25-30 years (vs 15-20 for felt)
• Why longer: Doesn't degrade, rot, or absorb moisture
• Benefit: Lasts as long as shingles

6. Slip-Resistant

• Textured surface: Better traction for installers
• Safety: Reduces slip risk
• vs felt: Felt is slippery when wet

Disadvantages of Synthetic Underlayment

1. Higher Cost

• Materials: $25-40/square (vs $10-15 for felt)
• Typical roof: $400-700 more than felt

2. Can Be Slippery When Wet (Some Brands)

• Smooth synthetics: Can be slippery
• Solution: Choose textured/slip-resistant brands

FELT UNDERLAYMENT (#15)

What is Felt Underlayment?

Materials:

• Base: Organic paper or fiberglass mat
• Coating: Asphalt saturation
• Weight: #15 felt = 15 lbs per 100 sq ft (most common)

History:

• Used for 100+ years
• Traditional choice
• Still code-compliant

Advantages of Felt Underlayment

1. Lower Cost

• Materials: $10-15/square (60-70% cheaper than synthetic)
• Typical roof: $400-700 savings vs synthetic

2. Proven Track Record

• 100+ years: Time-tested
• Reliable: Known performance

3. Code Compliant

• Meets code: BC Building Code accepts #15 felt
• Minimum standard: Acceptable for permits

Disadvantages of Felt Underlayment

1. Tears Easily

• Fragile: Rips when walked on
• Wind damage: Can blow off before shingles installed
• Installation: Requires care, slower

2. Absorbs Water

• Organic base: Paper absorbs moisture
• Wrinkles: Wrinkles when wet, doesn't flatten
• Problem: Wrinkles create bumps under shingles

3. Poor UV Resistance

• Exposure limit: 2-7 days before degrades
• Problem: If project delayed, felt deteriorates
• Fraser Valley: Rain delays common (felt gets damaged)

4. Heavy

• Weight: 50-70% heavier than synthetic
• Handling: Harder to carry up ladder
• Labor: Slower installation

5. Shorter Lifespan

• Lifespan: 15-20 years
• Degradation: Organic base rots over time
• Problem: May fail before shingles (25-30 year shingles)

6. Slippery When Wet

• Safety hazard: Very slippery in rain
• Installation: Dangerous to work on

COST COMPARISON

Materials Cost (Fraser Valley, 2026)

Synthetic Underlayment:

• Per square: $25-40
• Small roof (15 squares): $375-600
• Medium roof (25 squares): $625-1,000
• Large roof (35 squares): $875-1,400

Felt Underlayment (#15):

• Per square: $10-15
• Small roof (15 squares): $150-225
• Medium roof (25 squares): $250-375
• Large roof (35 squares): $350-525

Cost Difference:

• Small roof: $225-375 more for synthetic
• Medium roof: $375-625 more for synthetic
• Large roof: $525-875 more for synthetic

Is Synthetic Worth the Extra Cost?

YES - Here's Why:

• Longer lifespan: 25-30 years (vs 15-20 for felt)
• Better protection: Superior waterproofing
• Warranty requirement: Some shingle warranties require synthetic
• Resale value: Buyers expect quality underlayment
• Cost in context: $400-700 on $12,000-15,000 roof = 3-5%

FRASER VALLEY CONSIDERATIONS

Why Synthetic is Better for Fraser Valley

1. High Rainfall (170+ cm/year)

• Synthetic: Doesn't absorb water, stays flat
• Felt: Absorbs water, wrinkles, creates bumps

2. Frequent Rain Delays

• Synthetic: Can be exposed 30-180 days
• Felt: Degrades in 2-7 days (common problem)

3. Wind Events

• Synthetic: Won't tear or blow off
• Felt: Tears easily, blows off in wind

WHICH SHOULD YOU CHOOSE?

Choose Synthetic Underlayment If:

• Long-term home: Staying 10+ years
• Quality matters: Want best protection
• Premium shingles: Using architectural shingles
• Warranty important: Some require synthetic
• Fraser Valley: High rainfall, rain delays
• Best choice: 95% of our customers choose synthetic

Choose Felt Underlayment If:

• Extreme budget: Every dollar counts
• Rental property: Not your primary residence
• Short-term: Selling within 1-2 years
• Code minimum: Just need to pass inspection

The Bottom Line

Synthetic underlayment is superior in every way except cost. The extra $400-700 is a small price for better protection, longer lifespan, and peace of mind. In Fraser Valley's wet climate, synthetic is the clear choice.

At Dads Roof Repair, we install synthetic underlayment on 95% of roofs. We recommend synthetic for all owner-occupied homes. The small cost difference is more than offset by superior performance and longer lifespan. We only use felt when budget is the absolute only consideration.

Questions about underlayment? Call (778) 651-8021