Introduction: A Perfect Storm for Roofs

The Fraser Valley has one of the most challenging roofing climates in Canada. The combination of heavy rainfall, temperature swings, high humidity, and biological growth creates conditions that accelerate roof degradation. Understanding the science helps you protect your investment.

RAINFALL: THE PRIMARY CHALLENGE

Fraser Valley Precipitation Statistics

Annual Rainfall:

• Hope: 170 cm (67 inches) per year
• Chilliwack: 165 cm (65 inches) per year
• Agassiz: 180 cm (71 inches) per year
• Harrison Hot Springs: 200+ cm (79+ inches) per year

Comparison:

• Vancouver: 146 cm/year
• Seattle: 95 cm/year
• Toronto: 83 cm/year
• Calgary: 42 cm/year

Fraser Valley receives 2-4x more rain than most Canadian cities.

Rain Days vs. Rain Intensity

Rain Days:

• 150-180 days/year: At least some precipitation
• October-March: 20-25 rain days per month
• July-August: 5-8 rain days per month

Atmospheric Rivers (Pineapple Express):

• Frequency: 5-10 events per year
• Intensity: 50-150 mm (2-6 inches) in 24-48 hours
• Impact: Tests roof drainage capacity, finds every weak point

How Rain Damages Roofs

1. Water Infiltration:

• Capillary action: Water drawn into tiny cracks
• Wind-driven rain: Horizontal rain penetrates gaps
• Standing water: Overwhelmed drainage

2. Biological Growth:

• Moss: Thrives in constant moisture
• Algae: Black streaks (Gloeocapsa magma)
• Lichen: Symbiotic algae + fungus

3. Material Degradation:

• Hydrolysis: Water breaks chemical bonds
• Swelling/shrinking: Wood expands when wet, shrinks when dry
• Corrosion: Metal oxidation accelerated by moisture

TEMPERATURE: EXTREME SWINGS

Fraser Valley Temperature Range

Annual Range:

• Winter lows: -15°C to -20°C (5°F to -4°F)
• Summer highs: +35°C to +40°C (95°F to 104°F)
• Total range: 55-60°C (99-108°F)

Roof Surface Temperatures:

• Winter: -20°C to +10°C (-4°F to 50°F)
• Summer: +60°C to +80°C (140°F to 176°F) on dark shingles
• Daily swing: 30-50°C (54-90°F) in summer

Thermal Cycling Damage

Expansion and Contraction:

• Asphalt shingles: Expand/contract with temperature
• Metal roofing: Expands 0.012 inches per 10°F per 10 feet
• Wood deck: Expands/contracts with moisture AND temperature

Stress Points:

• Fasteners: Loosen from repeated expansion/contraction
• Seams: Gaps open and close
• Flashing: Metal expands more than surrounding materials

Freeze-Thaw Cycles

Fraser Valley Freeze-Thaw:

• Frequency: 30-50 cycles per winter
• Mechanism: Water expands 9% when frozen
• Damage: Cracks widen, materials split

Most Vulnerable Areas:

• North-facing slopes (stay frozen longer)
• Shaded areas (slower to thaw)
• Valleys (water accumulates)
• Eaves (ice dams form)

MOSS & ALGAE: BIOLOGICAL WARFARE

Why Fraser Valley is Moss Heaven

Perfect Conditions:

• Moisture: 150+ rain days/year
• Temperature: Mild (rarely below freezing)
• Shade: Tree coverage
• Humidity: 70-90% year-round
• pH: Slightly acidic rain (moss prefers pH 5-6)

Moss Growth Science

Life Cycle:

1. Spore landing: Wind-blown spores land on roof
2. Germination: Spore germinates in moisture
3. Rhizoid growth: Root-like structures penetrate shingle surface
4. Colony expansion: Moss spreads 1-2 cm/year
5. Maturation: Thick mat forms (1-3 cm thick)

How Moss Damages Roofs:

• Lifts shingles: Rhizoids grow under shingle edges
• Holds moisture: Moss acts like a sponge (10x its weight in water)
• Blocks drainage: Water backs up under shingles
• Accelerates degradation: Constant moisture breaks down asphalt

Algae: The Black Streaks

Gloeocapsa Magma:

• Type: Cyanobacteria (blue-green algae)
• Appearance: Black or dark green streaks
• Growth: Feeds on limestone filler in shingles
• Damage: Mostly cosmetic, but holds moisture

ICE DAMS: FRASER VALLEY'S WINTER CURSE

Ice Dam Formation Science

The Process:

1. Heat escapes attic: Poor insulation/ventilation
2. Roof deck warms: Snow melts on upper roof
3. Water flows down: Meltwater runs toward eaves
4. Refreezes at eaves: Eaves are cold (no heat from below)
5. Ice dam forms: Ice builds up, blocks drainage
6. Water backs up: Trapped water seeps under shingles

Why Fraser Valley Gets Ice Dams

Temperature Conditions:

• Daytime: Above freezing (0-5°C), snow melts
• Nighttime: Below freezing (-5 to -10°C), water refreezes
• Frequency: 10-20 freeze-thaw cycles per winter

Snowfall:

• Average: 100-150 cm (40-60 inches) per winter
• Wet snow: High water content (heavy, insulating)

Ice Dam Damage

Interior Damage:

• Water stains on ceilings
• Drywall damage
• Insulation saturation
• Mold growth

Roof Damage:

• Shingle lifting
• Deck rot
• Gutter damage (ice weight)

WIND: UNDERESTIMATED THREAT

Fraser Valley Wind Patterns

Prevailing Winds:

• Direction: West to east (follows valley)
• Speed: 10-20 km/h average
• Gusts: 50-80 km/h during storms

Extreme Events:

• Outflow winds: Cold air from interior BC (winter)
• Speed: 80-120 km/h (50-75 mph)
• Frequency: 2-5 events per winter

Wind Damage Mechanisms

Uplift Forces:

• Bernoulli effect: Fast-moving air creates low pressure above roof
• Suction: Pressure difference lifts shingles
• Critical areas: Edges, corners, ridges (highest uplift)

Why 6-Nail Protocol Matters:

• 4 nails: Code minimum, adequate for most areas
• 6 nails: 50% more holding power
• Fraser Valley: Wind exposure justifies 6-nail

HUMIDITY: THE HIDDEN ENEMY

Fraser Valley Humidity Levels

Relative Humidity:

• Winter: 80-90% (very high)
• Summer: 50-70% (moderate to high)
• Year-round average: 70-75%

Condensation Science

Dew Point:

• Definition: Temperature at which air becomes saturated (100% RH)
• Condensation: When surface temp drops below dew point, water condenses
• Attic problem: Warm, moist air from house meets cold roof deck

Why Ventilation is Critical:

• Air exchange: Removes moist air before condensation
• Temperature control: Keeps attic temp close to outside temp
• Prevents: Mold, rot, ice dams

CLIMATE CHANGE IMPACTS

Observed Trends in Fraser Valley

Temperature:

• Warming: +1.5°C since 1950
• Heat waves: More frequent, more intense (2021: 49.6°C in Lytton)
• Milder winters: Fewer extreme cold snaps

Precipitation:

• Total: Increasing slightly
• Intensity: More extreme events (atmospheric rivers)
• Snow: Less total, but more variable

Roofing Implications

Adaptations Needed:

• Higher wind ratings: More extreme storms
• Better drainage: Handle intense rainfall
• Heat resistance: Materials must handle 45°C+ days
• Longer-lasting materials: Reduce replacement frequency

The Bottom Line

Fraser Valley's climate is uniquely challenging for roofs. Heavy rain, temperature swings, moss growth, ice dams, and high humidity all accelerate degradation. Understanding the science helps you choose materials and maintenance strategies that work.

At Dads Roof Repair, we design roofs for Fraser Valley climate. We use synthetic underlayment (handles moisture), extended ice shield (prevents ice dam damage), 6-nail protocol (wind resistance), and proper ventilation (controls humidity). We understand the science.

Want a roof built for Fraser Valley weather? Call (778) 651-8021