What Factors Affect the Rates of Physical Weathering?

Written by steve lanore
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What Factors Affect the Rates of Physical Weathering?
Cracks may form in concrete as a result of freezing and expanding over time. (Jupiterimages/Photos.com/Getty Images)

Weathering is caused by several factors and each affect materials in varying ways. For instance, hail does not harm a driveway, but it can destroy a roof. Items subject to weathering have a life expectancy based on their design and the climate in which they are used. The rates of physical weathering might involve two or more environmental factors working together. Extreme conditions will often accelerate physical weathering. Improper building maintenance can allow a minor condition under normal circumstances to cause a major failure if left unattended.

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Solar Weathering

Weathering from the sun is correlated to the highest sun angle at noon, the length of the day and the altitude. A high sun angle allows more of the visible and invisible wavelengths to reach the Earth's surface. A lower sun angle allows the atmosphere to diffuse more of the radiation, and also provides shielding in shadows. Solar exposure causes a daily expand-and-contract cycle, which degrades the construction components more quickly than in a cloudy climate.

What Factors Affect the Rates of Physical Weathering?
The sun beats relentlessly on everything exposed to it. (Jupiterimages/Photos.com/Getty Images)

Temperature Extremes Weathering

Heat stress is governed by frequency and intensity of high-temperature episodes. For instance, a home in Phoenix, Arizona, will need to have a higher heat endurance than a home in Chicago, Illinois, on average. The attic temperature may reach 71.1 degrees Celsius in a hot climate, which breaks down air duct work and insulation faster compared to a more moderate climate. Hot, moisture-laden air will condense within the cooler interior walls of the home and can lead to mould production and a serious weathering of wood and insulation materials over time. The rate of exterior heat stress is somewhat dependent on the wind. A 20-mph breeze will carry more heat away from a roof or sun-exposed siding, providing a cooling effect a calm day would not offer. Humidity also affects the rate of high-temperature weathering. More energy is required to heat a moist surface than a dry one, so the rate of heat transference between materials and through the air itself will be moderated by higher moisture content.

Cold temperatures cause a contraction of building materials and also a drying effect. Weathering increases when the cold is accompanied by very low relative humidity or wind. The rate of cold weathering will be sped up in a building with improper insulation or worn siding. Cold weathering rates are decreased for buildings well sheltered with trees and shrubs.

Wind, Water Effects

Wind causes pressure differences between the upwind and downwind sides of the structure. Vents built into the structure attempt to prevent this, but wind intrusion is unavoidable over time as materials degrade. Wind drives dust, pollen, insects and water into the siding, roofing and trim. Frequent high-wind episodes will dry out wood leading to cracking and warping. Higher wind speeds also degrade rubber seals around doors and windows faster. Water intrusion anywhere into a building is going to accelerate weathering in the form of warped roof decking and foundation cracks from expanding and contracting soil.

Storm Effects

Hail can destroy a roof in a few minutes. Depending on hail size, the shingle gravel may be worn away with small hail, or the shingles and underlying decking can be cracked and lose their watertight seal with large hail. High winds will pull at shingles. This may go unnoticed from the ground, but each high-wind event speeds up the weathering process by allowing cracks to form in roof seals and shingles to loosen. Water intrusion into the structure from minor flooding can destroy dry wall and cause wood to swell. Moisture pockets in a building will allow mould to form and this can result in great expense to remove it.

Tree and Gutter

Improperly maintained trees can grow until limbs scrape against the roof as the wind blows. This wears away at the shingles and may rub a hole through to the decking. Tree friction in combination with normal rain and wind events can cause severe water damage to the decking, greatly shortening roof life. Leaf-clogged gutters lead to water overflow during precipitation events. This weakens the adjoining wood causing it to become soft, crack and fall off, leaving unprotected wood exposed to insect and water damage.

Combination Effects

Multiple weather elements tend to work together in a real-world situation. For example, ultraviolet solar radiation will lead to cracks in vinyl siding -- water then intrudes underneath the siding weakening the adhesive and causing wood rot. A severe ice storm (cold plus rain) will lead to much larger and more numerous cracks than either cold or rain alone. High altitude leads to a more extreme temperature because the dry air heats and cools over a wider daily range. Roofing materials tend to dry out and fail more quickly and the sunlight is more intense there. Altitude affects solar weathering because the air is 18 per cent thinner at 5,000 feet compared to sea level. The thinner air filters out less harmful radiation -- all else being equal, a high-altitude structure will weather more quickly than a lower location.

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