Building Envelope Systems and Assemblies

Building Envelope Systems and Assemblies Objectives

• Learners should be able to determine the relationship between a building's envelope and its other systems.
• Learners should understand the basic principles for selecting and applying building envelope systems.
• Learners should be able to articulate methods for improving a building envelope's efficiency.

Building Envelope

• Building envelopes physically separate indoor and outdoor environments.
• Envelopes consist of building materials that protect interior spaces from outdoor weather and climate changes.
• Building envelope materials and design depend on climate, culture, and available resources.

Envelope Systems of a Typical Building:

• Below Grade System
• Wall Systems
• Fenestration System
• Roof System
• Atria

Evolution

• The first building envelope was likely a cave, providing privacy and security.
• The earliest building envelopes were dome-shaped structures combining wall and roof.
• Early on, timber frames and masonry walls became the two dominant envelope forms.
• Eventually, roofs, walls, and floors became distinct building envelope elements.
• The invention of the steel frame in the 19th century marked the beginning of today's building envelope concept.
• However, steel frames were initially hidden within masonry walls.
• The modern architectural revolution began in the early 20th century.
• By mid-century, steel or concrete frame office buildings with lightweight metal and glass curtain walls became common for commercial and institutional buildings.

Function and Performance

• Four function categories are defined below:

Structural Support Function

• Supports, resists, transfers, and accommodates all structural loading forms from interior and exterior environments, the enclosure, and the building itself.

Environmental Control Function

• Controls, regulates, and moderates loadings due to the separation of interior and exterior environments.
• Largely this concerns the flow of mass and energy

Finish Functions

• Interfaces of the enclosure within the interior and exterior environments.
• Each interface must meet relevant visual, aesthetic, and wear requirements

Distribution Function

• Distributes services or utilities such as power, communication, security, water, gas, and air-conditioning to, from and within the enclosure.

Distinct Functions:

• Structural: For walls not part of the main structure, it supports its own weight and transfers lateral loads to the building frame.
• Water: Resists water penetration.
• Air: Resists excessive air infiltration.
• Condensation: Resists condensation on interior surfaces under service conditions.
• Movement: Accommodates differential movement caused by moisture, temperature variations, and structural movement.
• Energy conservation: Resists thermal transfer through radiation, convection, and conduction.
• Sound: Attenuates sound transmission.
• Fire Safety: Provides rated resistance to heat and smoke.
• Security: Protects occupants from outside threats.
• Maintainability: Allows access to components for maintenance, restoration, and replacement.
• Constructability: Provides adequate clearance, alignments, and sequencing for integrating components during construction.
• Durability: Provides functional and aesthetic characteristics for an extended time.
• Aesthetics: Performs all functions while being visually attractive.
• Economy: Achieves all the above inexpensively.
• Performance refers to the required level or standard for each functional requirement.

Major Performance Issues:

• Thermal performance
• Moisture protection
• Fire safety
• Acoustics
• Daylight and perimeter visual environment
• System maintainability
• Material durability

Specialized Building Performance Issues:

• Seismic safety
• Protection against blast and chemical, biological, and radiological (CBR) attack
• Safety against extreme wind.
• General safety against wind loads
• Indoor air quality and mold prevention
• Sustainability and HVAC integration

Below Grade System

• A below grade system refers to areas below ground level, often called basements.
• These areas provide functional spaces for storage, offices, mechanical/electrical rooms, parking, tunnels, and crawlspaces.

Three Main Elements:

• Foundation Walls
• Slabs on Grade
• Plaza Decks
• Successful below grade building enclosure systems depend largely on the ability to control moisture.

Foundation Walls

• Common materials for foundation walls and below grade building enclosure systems:

Drainage Materials:

• Aggregate Drainage Layer: Includes graded pea-gravel aggregate or coarse sand.
• Prefabricated Synthetic Drainage Layer: Consists of plastic composite drainage cores with geotextile fabrics.
• Filter Fabrics: Geotextile filter fabrics separate different soil types in below grade enclosure applications.

Dampproofing

• Controls vapor diffusion through the foundation, reducing damp conditions inside.
• Often bitumen-based coatings, typically 0.25mm thick, can be solvent or water emulsion.

Waterproofing Membranes

• Can be post-applied or pre-applied for positive-side, negative-side, or blind-side applications.
• Positive-side systems are applied to the exterior of the foundation wall that is directly exposed.
• Negative-side systems are applied to the interior of the foundation wall, opposite the exposed surface.
• Blind-side systems are pre-applied where the concrete element will be that is directly exposed to moisture.

Four Types of Waterproofing Membranes:

• Fluid-Applied Systems: Includes urethanes, rubbers, plastics, and modified asphalts.
• Sheet-Membrane Systems: Includes thermoplastics, vulcanizing rubbers, and rubberized asphalts.
• Bentonite Clays: Includes composite sodium bentonite systems with HDPE liners and geotextile fabrics.
• Cementitious Systems: Contains Portland cement and sand combined with a waterproofing agent.

Protection Board

• Shields waterproofing membranes from construction damage, backfill materials, and ultraviolet radiation.
• Most commonly, it's a semi-flexible sheet with an asphalt core between asphalt-impregnated glass fiber mats.

Insulation Materials

• Primarily limited to rigid extruded polystyrene board due to high compressive strength and moisture absorption resistance.

Waterstops

• Utilized at construction joints in below grade walls, footing slabs, and other elements requiring waterproofing.
• Provides a secondary barrier against water passage across construction joints.
• Common materials include polyvinyl chloride (PVC), neoprene, expanding sodium bentonite, and thermoplastic rubber.

Drainage Pipe

• Typically 4" or 6" in diameter, made of corrugated PVC or polyethylene, or sometimes porous concrete.

Slab on Grade

• Common materials in floor slab systems:
• Finish Floor Covering: Exposed concrete or various floor coverings like wood, vinyl, or carpet.
• Concrete Floor Slab: 4" to 6" thick concrete reinforced with welded wire fabric at mid-depth.
• Under Slab Vapor Retarder or Waterproofing Membrane: May include polyethylene sheets, polyolefin sheets, or asphalt/polyethylene composite sheets.
• Waterproofing of the slab on grade is necessary to resist hydrostatic pressures.
• Capillary Break Layer: Typically 6" to 8" thick layer of ¼" granular materials graded to increase drainage.
• The granular material serves as a capillary break and a place to store water and allows it to be absorbed back into the surrounding soil.

Plaza Deck

• A plaza deck system is any supported slab providing greenscape, tree planters, and/or vehicle and pedestrian movement over occupied space.
• Basic components of a plaza deck system:

Wearing surface:

• Any surface subjected to pedestrian or vehicular traffic.
• Concrete, brick pavers, granite paving blocks, asphalt paving blocks and/or pre-cast elements.

Fill Slab:

• Anything that occupies space on the plaza deck above the membrane and below the wearing surface.
• Graded sand, asphalt materials, pea gravel or a sand-cement mortal setting bed is used.
• More recently, extruded or expanded polystyrene insulation, loose earth or lightweight concrete are used on horizontal applications of plaza deck to fill these layers.

Isolation Layer/Drainage Layers and Flow Path System

• Consists of pea gravel and/or separator fabric over pea gravel.
• Common for isolation components consist of a combination of geo-synthetic materials and pea stone drainage fill.

Membrane and Protective Layer

• Includes a special waterproofing membrane to prevent moisture leakage into the occupied space below.
• Insulation can also be provided directly on the top of the membrane and protection layer to promote long-term system durability.

Structural Support Systems

• Any of the basic slab design.
• It can be 2-way flat plate slab, one-way slab on beam, post tensional slab-beam system or precast system.

Wall Systems

• An exterior wall typically forms part of a building envelope, separating the accommodation inside from that outside.

Basic Elements or Layers of an Exterior Wall:

• Exterior Cladding (Natural or Synthetic): The protective layer or finish affixed to the exterior side of a building enclosure.
• Drainage Planes: Any element exposed to weather or otherwise residing at the line between the "wet" and "dry" zones of an exterior wall system or assembly.
• Air Barrier Systems: Any element, or combination of elements, that is intended, by design to control the movement of air across an exterior wall system.
• Vapor Retarder: Any element that is intended to control or otherwise limit the flow of water in its vapor form across and exterior wall system.
• Insulating Elements: Any element, or combination of elements, that is intended to control or otherwise regulate heat loss and heat gain across an exterior wall system.
• Structural Elements: Any element, or combination of elements, in an exterior wall system that is intended to effectively resist both live and dead loads acting on a building or structure through the efficient and effective distribution of those loads to the underlying structural frames.Several of these layers may serve multiple purposes.

Cast-in-Place Concrete

• Generally defined by the building's structural system including the vertical structural supports and lateral supports for wind and seismic activity.

Exterior Insulation and Finish System (EIFS)

• An exterior wall cladding that utilizes rigid insulation boards on the exterior of the wall sheathing with a plaster appearance exterior skin.
• The most common type of EIFS is the polymer based (PB) system and less common type is the polymer modified system.
• IEIFS can be a barrier wall system or wall drainage system.

Masonry Wall System

• Can be used to form a durable cladding and to achieve various aesthetic effects.
• It can also serve as a portion as a structural framing for the building.
• Typically increase the fire resistance of the wall system or structural elements.
• Several different types of masonry units are commonly used.
• Common masonry unit types include clay and concrete units, which may be solid or hollow, and glazed or unglazed.
• Other masonry unit types include cast stone and calcium silicate units.

Panelized Metal Wall System

• Metal panels can be aluminum, stainless steel, copper or steel.
• Aluminum is the most common material used due to its cost, corrosion resistance, and durability. In high-end applications, stainless steel and copper can also be used.
• Several manufacturers fabricate steel panel systems, which require protective coatings for resistance to corrosion.
• Types of metal panel system:
  • Lap-Seam Metal Panels: Formed out of metal sheets and typically ship-lapped with adjacent panels.
  • Composite Metal Wall Panels: Feature two sheets of metal adhered to a core material; usually stronger than lap-seam panels.
  • Flat Plate Metal Wall Panels: Typically fabricated out of 1/8-inch-thick metal plate; high impact resistance and durability.
  • Metal-Faced Composite Panels: Consist of metal facings adhered to a thin thermoplastic core.

Pre-cast Concrete Wall System:

• Offer a wide variety of shapes, colors, textures, and finishes.
• Typically, each pre-cast panel is independently supported to the building structure.
• Joints around each of the precast panels are usually filled with sealant.
• In some cases, pre-cast panels are used as formwork for cast-in-place concrete.
• Cladding or Curtain Walls are the most common use of pre-cast concrete for building envelope.
• They are only designed to resist wind, seismic forces generated by their own weight, and forces required to transfer the weight of the panel to the support.
• Load-bearing wall units resist and transfer loads from other elements.
• Pre-cast concrete shear wall panels -used to provide lateral load resisting system when combined with diaphragm action of the floor construction.

Thin Stone Wall System

• Typically consist of stone panels ranging in thickness from 3/4 inches to 2 inches. Most panels are fabricated from granite, while marble; limestone, travertine, and sandstone are also used to a lesser extent.

Fenestration Systems

• Fenestration refers to the openings in the building envelope, including the installation of windows, doors, and skylights.

Components: Curtain Wall

• The most common framed wall is aluminum and contains in-fills of glass, metal panels, or thin stone.
• Commonly used curtain wall framing methods:
  • Stick Systems: Install the curtain wall frame (mullions) and glass or opaque panels and connect together piece by piece.
  • Unitized or Modular Systems: Construct the curtain wall of large units are assembled/glazed in the factory; then you can ship to site and erect on the building.

Moisture Protection for Curtain Walls

• Water-managed: No effort is made to create an air barrier on each glass or spandrel unit, so a larger amount of water is forced into the system and must be wiped away.
• Pressure-equalizer: Blocks all the forces that can drive water across a barrier.

Exterior Doors

• Entrance and exit doors generally serve as building entrances for the general public or as service entrances for building operations personnel.
• Commonly used door materials include aluminum, steel, wood and glass.
• Doors that are integrated with commercial storefronts are typically aluminum frames with glass in-fills, or all glass. Doors can swing, revolve or for industrial purposes such as overhead to maintain security.

Glazing

• Glass has been used for thousands of years to allow daylight into buildings, while providing weather protection.
• Commonly used glass and glazing components:
  • Annealed glass: Most commonly used architectural glass.
  • Heat-strengthened glass: Twice the strength and breakage resistance from wind or thermal stress like annealed glass.
  • Fully-tempered glass: Provides at least four times the strength of annealed glass, give superior resistance to breakage.
  • Laminated glass: Consists of two or more lites of glass glazing in skylights.
  • Coated glass: Covered with reflective or low-emissivity coating.
  • Tinted glass: Contains minerals that color the glass uniformly through its thickness.
  • Insulating glass units (ig units) Consists of two or more lites of glass with a continuous spacer that encloses a sealed air space.

Sloped Glazing

• Skylights have been used for over a century to provide interior daylighting.

Typical skylight components:

• Supporting members such as rafters, cross bars and pressure bars to support the roof against the elements like rain.
• Infill panels such as glass, fiberglass sheets, and fiberglass sandwich panels; generally glass.

Windows

• Commonly used window frame materials include aluminum, vinyl, fiberglass, steel wood, and PVC.
• Aluminum frames are the most widely used window frame material, and provide design flexibility because of the wide range of available stock systems.
• Wood, vinyl and fiberglass are the most widely used window frames in the residential market.
• Common frame options that can be fixed or movable:
  • Movable window categories are sliding or compressional

Compressional seal windows:

• Awning
• Hopper
• Casement
• Vertically or horizontally pivoted windows

Sliding seal windows:

• Hung windows
• Horizontal sliding windows
• Pivot/jalousie windows have poorer resistance

Roof Systems

• Fundamental in protecting buildings from moisture and other weather conditions.
• Commercial buildings either have low slope or flat roofs.

Materials for Roof Coverings:

• Low-slope Roof Coverings:
  • Built-up Roofs (BUR): Alternating bitumen and reinforcement sheets.
  • Mesh Reinforced Elastomeric Coatings (MREC): Acrylic and polyester.
  • Modified Bitumen (MB): Pre-fabricated with reinforcement layer.
  • Atactic Polypropylene (APP): APP polymer blended with asphalt and fillers.
  • Styrene-Butadiene-Styrene (SBS): SBS polymer is blended with asphalt and fillers; Styrene-Ethylene-Styrene (SEBS).
  • SEBS is blended to asphalt.
  • Thermoplastic Single-Plies Thermoplastic Single-Plies these sheets are normally around 5 - 12 feet wide some manufacturers weld in factory to form large sheets. Thermoplastic Polyolefin (TPO) is typically white and can be 3.6M wide
  • Thermoset Single-Plies bond with adhesive or formulated tape

Steeper Roof Coverings:

Asphault, wood and metal options depending on location, water runoff needs vary.

Atrium System

• A term for an interior court with multiple stories.