Building Envelope Failures Contributing Factors

Building Envelope Failures Contributing Factors




Water related factors of decline to buildings may take the largest toll on structures which are snow, rain, moisture, internal condensation, and humidity. Biological factors include fungi, bacteria, and insects. Chemical contributors may include oxidizing agents, i.e bleach, reducing agents, i.e. sulfides, acids, i.e. bird droppings, bases, i.e lime, salts, i.e. chlorides, or already chemically neutral substances such as fat or oil. Solar radiation, air quality, freeze thaw effects and wind are other environmental contributors to building decline.

The majority of building envelope failures can be credited to water, in one of its many forms (gas, liquid, and substantial). The supplies of water that could affect a building envelope include:

Water ingress and absorption. Water ingress is typically a function of moisture load and surrounding resistance. Most materials or systems have the capability to absorb some water for a defined period of time without degradation..If absorbed moisture is allowed to sufficiently dry prior to the period which degradation will occur, then these materials could unprotected to reasonable durability despite the absorption of water. surrounding assemblies can show signs of water entry due to forces such as gravity, capillary action, or wind blown water. Material decline can occur if the water ingress cannot be managed or drained to the exterior, or if materials do not have the capability to store water without degradation.

Condensation. Condensation occurs on a surface with a temperature below the dew point of the air in which it exists. The likelihood or extent of condensation is related to the relative humidity of the air and material temperatures. Problematic condensation within building envelopes is often related to uncontrolled air leakage, vapor spread, rain penetration, or snow melt. Condensation is typically controlled by the careful design and installation of air and vapor barriers.

High RH levels. Although condensation is typically the consequence of high micro climate RH levels, situations can exist where materials are damaged due to consistent high RH levels without condensation (i.e. mold growth)

decline factors in concrete

o Physical processes – freeze / thaw, abrasion, thermal cracking

o Carbonation and ingress of chlorides, leading to a risk of reinforcement corrosion in the presence of water and oxygen

o Chemical attack – includes the external attack of sulfates and acids, and internal attack of alkali aggregate reaction.

decline factors in steel

o Corrosion is a major decline factor in steel, which need a combination of water and oxygen to corrode.

o Corrosion may be provoked by particularly aggressive environments.

decline factors in timber

Main durability risk factors in timber are moisture, insects and fungi. From these, the following durability issues can arise:

o Deformation of members due to moisture movement

o Fungal decay (dry and wet decay) and insect attack ( wood boring beetles and termites)

o Structural performance occurrences can occur like reduction in strength and stiffness.

Air and Air Pollutants

Air and its elements – oxygen, nitrogen, and other by-products can be an agent for decline, in addition as a transportation mechanism. As a transportation mechanism, air can bring moisture, water, and pollutants to areas of the building envelope that would typically be protected from these agents. Moist air traveling by a building envelope can consequence in mold growth on organic materials or corrosion on metallic materials. shared air contaminants include chlorides in maritime climates, sulphur dioxide from means emissions, hydrochloric acid near manufacturing plants, nitric acid from fossil fuel combustion, and chlorine in pool environments. Buildings located in environments with these high concentrations of reactive contaminants can experience more rapid degradation of a variety of building envelope elements.

Wind

Wind plays an important role in the service life of building materials. surrounding design requires consideration for peak loading in addition as cyclical loads that cause shortened life from “overworked” materials. Wind loading can also cause depressurization of surrounding cavities, which can increase air leakage, water ingress, moisture movement and condensation. Wind pressures are also responsible for uplift on roofing assemblies and wind pushed rain that can penetrate unprotected areas.

Biological and Ecological Agents

Molds or fungi, in addition as rodents, insects, and birds can affect the service life of building materials. The presence of fungi, tempered air and moisture (typically above 22% moisture content in wood materials) can cause decline of organic materials and unacceptable occupant health conditions.

Insects, birds, and rodents can damage materials by digesting, gnawing, nesting or depositing corrosive droppings. Vegetation in the form of vertical vines or horizontal landscaping can considerably impact building fascades and structural elements due to root growth.

Temperature

Extreme temperatures or temperature fluctuations can cause meaningful movement in materials like copper and vinyl, creating deformation of materials, and unintended gaps and hole at material junctures. halting temperature can rule to frost heaving, ice jacking, spalling of masonry and damage to brittle materials. Excessive heating of materials (i.e. metal flashing and roofing can rule to “bleeding” of materials onto finished cladding, and material cracking, bulging or ridging. Extremely hot temperature, such as those that might occur in building fires can have a multitude of detrimental effects with respect to service life. These temperatures can temporarily or permanently change the physical similarities of materials, making them ineffective for their intended use.

Solar Radiation

Material selection and the assembled surrounding can be greatly influenced by UV radiation from the sun. When material absorbs radiation from the sun, energy is produced that can cause a chemical reaction and material character changes (i.e., becoming brittle, yellowing, chalking, or fading). Most assemblies with UV sensitive material require the use of a covering material (i.e., metal flashing over exposed roofing membrane), limiting building aesthetic and design options. Other materials have limited service life as a consequence of UV degradation (i.e., many sealant materials and water based paint finishes). Conversely, night sky radiation can also cause heat loss and problems with condensation and corrosion in some roofing assemblies (i.e. zinc roofing)

Chemical responses and Incompatibility

Although chemical responses are not a specific environmental agent, they are typically coupled with environmental agents to cause damage (i.e. corrosion).

For example, galvanic corrosion is a typical problem with incompatibility between metals, or the use of pressure treated wood and zinc coated fasteners. Other compatibility issues include the use of various coatings, caulking, and membranes in contact with each other.

Positive Aspects of Agents Affecting Building Durability

There are some positive side effects that impact the service life due of building materials. For example, patina corrosion protects copper roofs, temperature shifts dry moist materials, landscaped or green roofs protect UV sensitive roofing materials, wind cools buildings, and water running over zinc strips minimizes algae growth.

HOW CAN DURABILITY AND SERVICE LIFE BE IMPROVED?

The main culprits that can rob durability are poor workmanship and without of knowledge of the similarities of materials. It is important to clarify the problems that manifest themselves as shortcomings in our traditional materials and look for opportunities to enhance material performance in housing and buildings. analyze new techniques, materials, elements and systems that potential to enhance durability while reducing life-cycle costs. Develop methods for accelerated assessment of materials, elements and systems that mirror in-place builder installed performance. Greater attention should be paid to details which influence how a structure deals with water run off and drainage.

Building elements require varying degrees of maintenance, repair and substitute during the life cycle of a building. The extent and intensity of maintenance, repair and substitute varies considerably, depending on how appropriately the service life of materials, assemblies, and systems are harmonized, and how easy to reach they are for regular maintenance, and replacements.




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