CE 35 – Building Systems Design PDF

Central Mindanao University College of Engineering Department of Civil Engineering Lecture Notes in CE 35 – Building Systems Design...

Central Mindanao University College of Engineering Department of Civil Engineering Lecture Notes in CE 35 – Building Systems Design UNIT III –Building Envelope Systems and Assemblies BUILDING ENVELOPE The building envelope is a physical separator between the exterior and the interior of the building and fenestration systems. The building envelope is the physical barrier between the exterior and interior environments enclosing a structure. Generally, the building envelope is comprised of a series of components and systems (see figure 1) that protect the interior space from the effects of the environment like precipitation, wind, temperature, humidity, and ultraviolet radiation. The internal environment is comprised of the occupants, furnishings, building materials, lighting, machinery, equipment, and the HVAC (heating, ventilation, and air conditioning) system. Opaque components include walls, roofs, slabs on grade (in touch with the ground), basement walls, and opaque doors. Fenestration systems include windows, skylights, ventilators, and doors that are more than one- half glazed. The envelope protects the building’s interior and occupants from the weather conditions and shields them from other external factors e.g. noise, air pollution, etc. Envelope design strongly affects the visual and thermal comfort of the occupants, as well as energy consumption in the building. FUNCTION: A building envelope serves many functions. These functions can be divided into 3 categories: Support: to ensure strength and rigidity; providing structural support against internal and external loads and forces. Control: to control the exchange of water, air, condensation and heat between the interior and exterior of the building. Finish: this is for aesthetic purposes. To make the building look attractive while still performing support and control functions. PHYSICAL COMPONENTS: The building envelope includes the materials that comprise the foundation, wall assembly, roofing systems, glazing, doors, and any other penetrations. The connections and compatibility between these elements are critical to ensure that the building envelope functions as intended. Foundation The foundation is the structural component that transmits the loads from the building to the underlying substrate. Typically, some combination of reinforced concrete walls, slabs, and footings constitute the structural components of the foundation. However, the foundation must also be designed to control the transfer of moisture and thermal energy into the interior space.  The transfer of thermal energy through the foundation can be controlled by providing insulation between the interior and exterior environments; however, in some cases, the foundation insulation is neglected to reduce construction costs. Waterproofing the foundation is typically completed by applying a liquid applied asphaltic damp proofing. Additional waterproofing products such as sheet-applied membranes, liquid membranes, cementitious waterproofing, and built-up systems are also viable options. Drainage around the perimeter of the foundation must be provided to prevent long-term underwater submersion of the waterproofing membrane. One example of a perimeter foundation drain is a weeping tile placed in a trench complete with gravel ballast backfill, also known as a french drain. In some cases, a sump pit and pump system will be required in addition to the perimeter drain. Wall Assembly The wall assembly consists of a system of components that fulfill the support, control, and finish the function of the building envelope. While the precise placement and configuration of each component may vary between climates and individual buildings, the following components are typically found in the wall assembly (from the exterior to interior): Exterior cladding Exterior sheathing membrane Exterior sheathing Insulation Structural components Vapor barrier Interior sheathing Roofing System The roofing system is an important part of any house, as it keeps the weather out. It consists of shingles on the outside, which are on top of tar sheeting as a vapor barrier. Inside of the tar paper is wood sheathing. Beyond this, the attic areas in most houses are insulated with fiberglass spray insulation. It tends to be fluffy, pink fiberglass. Inhaling fiberglass is extremely bad for a person's respiratory system, so it is important to wear a mask if this insulation type is in one's roofing system. Glazing Glazing refers to the panels in windows, doors, and skylights - usually glass - that let light through. Door Doors are included in the housing envelope as they tend to be the biggest holes in the envelope. Having outer doors that seal well drastically improves the thermal efficiency of a house. Other Penetrations These may include a chimney or vents for a dryer or stove. FUNDAMENTALS OF PERFORMANCE The performance of the building envelope is impacted by a number of sub systems, ‐ such as heating, cooling and ventilating equipment, plumbing, and electrical systems. The interaction of the sub systems with the components of the building envelope, as well as certain activities of the occupants, can affect the performance of the building envelope. The building envelope should keep out: temperature extremes; moisture, as vapor or liquid; dust; and wind Additionally, to maintain durability, the building envelope should not permit weather elements to be trapped inside the walls. This may cause wall components to deteriorate, and continue to decay. In the early stages, it can usually be remedied relatively inexpensively. As time progresses, costs increase exponentially. There are numerous factors in the considerations of the fundamentals of performance: Axis. It is a line established by two separate points in space. It defines the points at which shape and spaces can be set in an asymmetrical and a balanced way. Symmetry. It is the balanced division and collection of all equivalent forms and spaces on also sides of the separating plane or regarding its center axis. Hierarchy. It articulates the importance and significance of a shape or space by the assist of its size shape as well as placement. Rhythm. It is a unifying movement that is characterized by a patterned repetition or an alteration of the formal elements. Datum. It defines a line plane or volume that serves together, measure, as well as organize a pattern of form and spaces. Transformation. It is the principal of retaining an architectural design idea or association and strengthening as well as building it through a sequence of discrete transformations. Products, best practices, building methods, and construction theories that are the best in one part of the country are not likely the best practices in another part of the country. In many areas, local government ordinances and building codes are trying to bridge the gap between the universal standard and the local standard. However, these codes are often just the minimum acceptable standards, and may not be the best procedures possible. Further variance in building envelope requirements can even occur within the same climate. Two homes in the exact same region, state, county, or even neighborhood may need different kinds of building envelopes. One home may see more direct sunlight, while the other may be at the bottom of a hill and prone to flooding. Even the direction the home is plotted can have some bearing. This makes it important to rely on experts that understand how all these things can be applied and work together. More importantly, it is important to discuss how these things do not work against each other as well. When the right people with the right knowledge get behind the wheel, a truly proper building envelope can be created. AESTHETICS "The building envelope is more than a façade−it is the poetic mediation between an internal spatial realm and the outside world." -Antoine Predock, FAIA, 2006 American Institute of Architects Gold Medalist. The fundamental goals of a successful building, regardless of location, aesthetics, program, owner, and building type, are essential to keep water out and allow thermal control within. The building envelope encompasses the entire exterior surface of a building, including walls, doors, and windows, which enclose, or envelop, the interior spaces. Weaknesses in the building envelope can result in several undesirable results, from moisture infiltration, often leading to mold and mildew; damage caused by wind loads, high energy costs, ongoing maintenance problems, and failure of one or more architectural and engineering building systems. Any of these scenarios, and the numerous ripple effects that may ensue, can potentially increase risk and liability concerns for architects, design professionals, building owners, and occupants. For these reasons, and the desire to promote sound professional design standards, a thorough understanding of building envelope design methods and construction techniques are critical aspects of architectural practice. When building envelope problems arise, liability concerns often focus on factors and parties relating to design, construction, manufacturing, and testing of systems and materials. Innovative architectural design is enhanced by careful attention to detailing, selection, and specification of compatible materials and related component systems. At the same time, architects, specifiers, and design professionals must be aware of component installation methods and construction techniques. With so many advances in manufacturing processes, emerging new materials, and enhanced technology in the marketplace, along with ongoing updates of building codes and industry testing criteria, and an often-unskilled labor force, the required knowledge base for effective building envelope design is constantly expanding. MOISTURE TRANSFER, DURABILITY, ENERGY AND MATERIAL RESOURCES The building sector accounts for 36% of national energy consumption (2010). About 50% to 70% of building energy is used for mechanical systems such as air conditioning and ventilation systems. The Philippine Green Building Code requires the adoption of efficient practices, designs, methods, and technology that can reduce energy consumption resulting in cost savings, reduced energy consumption, and reduced GHG emissions. Energy-efficient practices and technology can contribute to achieving green building objectives. Building envelope physically separates the indoor and outdoor environments. It encompasses the entire exterior surface of a building, including walls, roof, doors, and windows, which enclose, or envelope, the interior spaces. It is composed of layers of building materials that protect interior spaces from changes in outdoor weather and climate conditions. Some elements of a building envelope include: The following illustrates how a building envelope acts as a barrier between outdoor and indoor conditions. Air Tightness and Moisture Protection As the country’s humidity levels are high, the unwanted air infiltration and moisture ingress into indoor spaces can put additional load on the air-conditioning system and cause a detrimental impact on air quality. Thus, buildings must be planned, designed, and constructed with enough detail and quality to ensure maximum airtightness. The implementation of these measures requires only increased attention to the construction details and it can be implemented at practically no cost. Details should precisely include joints, including service entry joints, windows, and doors. Vapor barrier, a material that has a permeance of one perm or less, can also be installed. It prevents the entry of moisture through the walls and provides resistance to the transmission of water vapor from the outside to the inside of the building, which can burden the air-conditioning system operations. Design Application 1. SEALED WINDOW AND DOOR ASSEMBLIES: sealed by a continuous membrane along the joints between wall and window and door frames. Window and door assemblies should be complete with weather stripping and gaskets around the frames. Doors and windows are the first line of defense against humidity and moisture. 2. SEALED UTILITY SERVICES: Electrical, plumbing and mechanical piping, conduit or ducting penetrating through walls, floor, and ceiling should be sealed to reduce air leakage. Joints in the membrane should be caulked, lapped, and sealed or taped. 3. SEALED WALL, ROOFING, CEILING, AND FLOOR: tightly sealed with continuous water barrier or retarder, joint flashing, capping, sealants, and fillers. a) WALL - sealed with the application of a vapor/moisture barrier b) ROOF - sealed with complete ridge roll, flashing, valley, and joint terminations c) CEILING - joints and openings sealed with tape d) FLOOR - floor surfaces, joints, and terminations sealed with the application of water barrier, joint fillers, or airtightness tape. Waterproofing membrane overexposed roof or deck slabs while water barrier sheathing underexposed floor slabs on fill. Roof The roof shields a structure from harsh elements from sunshine to rain, so it is important to seal off and reinforce it. Wall The role of walls to act as moisture barrier are detailed in the illustrations below. Floor When it comes to moisture seepage, it is also important for floors to be treated and reinforced. Envelope Energy Flows From an energy flow perspective, the envelope is a composition of layers with varying thermal and permeability properties. The envelope may be composed of membranes, sheets, blocks, and preassembled components. The choice of the envelope is governed by climate, culture, and available materials. The range of choices in envelope design can be illustrated by two opposite design concepts: the open frame and the closed shell. In harsh climates, the designer frequently conceives the building envelope as a closed shell and proceeds to selectively punch holes in it to make limited and special contact with the outdoors. This may also be true where there are unwanted external influences such as noise or visual clutter. When external conditions are very close to the desired internal ones, the envelope often begins as an open structural frame, with pieces of the building skin selectively added to modify only a few outdoor forces. The flow of heat through a building envelope varies both by season (heat always flows from hot to cold and generally flows from a building in winter and to a building in summer) and by the path of the heat (through the materials of a building’s skin, or by outdoor air entering). These complexities must be considered by a designer who intends to deliver comfort and energy efficiency. Walls Understanding and optimizing the heat transfer through the walls is important in high-performance building design. Using thermal mass and insulation to your advantage with passive design strategies can help reduce the amount of energy that active systems need to use. Insulation Thermal insulation is a material that blocks or slows the flow of heat through the building envelope. Insulation is vital to most green building design because it allows spaces to retain what heat they have, while avoid gaining excess heat from outside. Total R-Values and Thermal Bridging In order to know the building's true thermal performance, you must calculate overall R-values for assemblies like walls, roofs, floors, and glazing. The total R value (or "overall" R-value) of an insulated assembly may be higher or lower than the R-value of the insulation, depending on the assembly's construction. Thermal bridging is when the overall R-value is lower than the insulation's R- value. Heat Transfer in Buildings Heat transfer takes place through walls, windows, and roofs in buildings from higher temperature to lower temperature in the following three ways: 1. Conduction: It is the transfer of heat by direct contact of particles of matter within a material or materials in physical contact. 2. Convection: It is the transfer of heat by the movement of a fluid (air or gas or liquid). 3. Radiation: It is the movement of energy/heat through space without relying on conduction through the air or by the movement of air. Heat transfer in buildings. Thermal Resistance of an Element Consisting of Homogenous Layers A building element is usually composed of a number of different materials. When materials are placed in series, their thermal resistances are added so that the same area will conduct less energy for a given temperature difference. The formation of air film at the surface of the wall or roof, due to convection movements of air, also provides resistance to the heat flow, similar to the construction material. The total resistance of the wall or roof includes all of the resistances of the individual materials that make it up as well as both the internal and external air-film resistance. Insulation It’s important to understand in a building to understand Heat Energy Flows and insulation. Insulation primarily is designed to prevent heat transfer from conduction and radiation. Resistance to conduction is measured by R-value (high thermal resistance =high R-value); Resistance to radiative heat transfer is measured by emissivity (high resistance =low emissivity and high reflectance). Conduction is the dominant factor when materials are touching each other; when there is an air gap between materials, radiation becomes important. Convection usually only becomes an issue when significant air pockets are involved. Materials used for insulation fall into two broad categories: Fibrous or cellular products –These resist conductions and can be either inorganic (such as glass, rock wool, slag wool, perlite, or vermiculite) or organic (such as cotton, synthetic fibers, cork, foamed rubber, or polystyrene). Metallic or metalized organic reflective membranes - These block radiation heat transfer and must face airspace to be effective. Insulation Materials Although insulation can be made from a variety of materials, it usually comes in five physical forms: batting, blown-in, loose-fill, rigid foam board, and reflective films. Each type is made to fit a particular part of a building. Batting/Blankets Form Factor & Installation: In the form of batts or continuous rolls that are hand-cut or trimmed to fit. Stuffed into spaces between studs or joists. Material: Fiberglass is manufactured from sand and recycled glass, and mineral fiber ("rock wool ") is made from basaltic rock and/or recycled material from steel mill wastes. Even recycled cotton fibers from jeans are used. Available with or without vapor and flame retarding facings. Blown-in/ Loose-Fill Form Factor & Installation: Loose fibers or fiber pellets are blown into building cavities using special pneumatic equipment. The best forms include adhesives that are co- sprayed with the fibers to avoid settling. Material: Fiberglass, rock wool, or cellulose. Cellulose is made from recycled plant material (such as newspaper) treated with fire-retardant chemicals. Benefits: Can provide additional resistance to air infiltration if the insulation is sufficiently dense. Foamed in Place Form Factor & Installation: Roll of foil, integrated into house wrap, or integrated into rigid insulation board. These “radiant barriers” are typically located between roof rafters, floor joists, or wall studs. Material: Fabricated from aluminum foil with a variety of backings such as craft paper, plastic film, polyethylene bubbles, or cardboard. Benefits: Resists radiative heat transfer. The resistance to heat flow depends on the heat flow direction – it is most effective in reducing downward heat flow. Infiltration & Moisture Control Water also moves through building envelope assemblies—in both liquid and vapor states. Unwanted infiltration can be a major cause of this. The focus here is upon the water vapor movement. Water vapor will often need to be handled by a climate control system through the use of energy (termed latent heat).