Designing Building Envelopes to Meet Sustainable and Aesthetic Goals Part 1 Brian Miller, P.E., LEED AP Precast/Prestressed Concrete Institute Brad Nesset Thermomass Introduction Webinar is in two parts Part one: Envelope systems overview Moisture and air management Part two (Feb. 15 or 17): Thermal resistance Aesthetics Introduction Building Envelope the system that separates indoor conditioned space from unconditioned space (the outdoors). Includes: Roof system Wall system Fenestration system Below grade system 1
Functional Requirements of Envelopes 1. Structural 2. Accommodate movement 3. Resist air infiltration and exfiltration 4. Resist water infiltration 5. Resist condensation 6. Energy conservation 7. Sound 8. Fire safety 9. Security 10. Aesthetics 11. Constructability 12. Maintainability 13. Durability 14. Economy Exterior Wall Systems Support loads (e.g. dead, live, wind, earthquake, blast) Control mass, energy and particulate flows (e.g. heat, air, moisture, smoke, fire, birds, insects, odor) Finish visual impact (color, form and texture) Distribution (if applicable) distribute services through a building Sustainability minimize environmental impact while optimizing building performance Sustainability Sustainable Sites Minimize site impact Reduce waste Reduce heat island effect Water Efficiency Energy and Atmosphere Minimize heat loss/gain to the conditioned space Materials and Resources Regionally made Contain recycled content/ or re-use 2
Sustainability Indoor Environmental Quality Rapid construction Control moisture intrusion resist mold Daylighting and views Occupant comfort Low emitting materials Acoustical performance Mold resistance Innovation in Design Basic Elements of Envelope Systems Wall System Exterior cladding (finish) Drainage plane Air barrier Vapor retarder Insulating elements Structural elements Interior wall (finish) Types of Exterior Wall Systems Cavity Wall (Rainscreen or Drained Wall) 3
Types of Exterior Wall Systems Barrier Wall (Face-sealed) Types of Exterior Wall Systems Mass Wall Common Exterior Wall Systems Masonry Thin stone (e.g. granite, marble, limestone, travertine, sandstone) 4
Common Exterior Wall Systems Cast-in place Concrete Exterior Insulated Finishing Systems (EIFS) Common Exterior Wall Systems Panelized Metal & Glass Curtain Walls Common Exterior Wall Systems Precast Concrete 5
Precast Concrete Walls Three Basic Types Sandwich Solid Wall Panel Thin-shell Load bearing and non-load bearing Available in essentially any shape and finish Wall Types - Solid Window walls, spandrels, shear walls, column covers, mullions Solid Walls Shapes 6
Wall Types Sandwich Wall Panels Sandwich Wall Panel Shapes Wall Types Stud and Cavity (Thin-shell) 7
Fenestration Systems Fenestration design of windows, entries, or other exterior openings in a building s envelope. Glass Windows Exterior Doors Skylights Moisture and Condensation Control Brad Nesset Thermomass Moisture & Condensation Control Good materials and good workmanship no longer constitute a high quality structure we must now understand how buildings work. Joseph Lstiburek, P. Eng. Building Science Corporation 8
Moisture & Condensation Control The cost of energy continues to escalate and moisture issues are growing with every failure. We can design the right way! Reduced insulation value Rot Mold Moisture & Condensation Control Why would a building have moisture problems? H-A-M (Heat, Air Infiltration, Moisture Management) Thermal bridging Penetration of rainwater into the wall at a joint. Condensation of moisture or frost formation on windows. Excessive leakage of warm, moist air either inside during summer or outside during winter Solutions need to Incorporate proper water control techniques Manage dew point Use continuous, edge-to-edge insulation strategies Design/install vapor retarder/barrier properly Mold The problems associated with moisture and its effects on building components are well known, and costly to repair. Most insurers have stopped coverage for these incidents leaving owners no other avenue for compensation but the court system. 9
Mold In general, mold demands a favorable combination of the following conditions to germinate, sporulate, and grow: Fungal spores settling on the surface Oxygen availability Optimal temperatures between 40 70 F Nutrient available (wood, paper, cellulose based materials) Moisture (liquid or relative humidity above 70%) The first four conditions are met in almost every building. The key remaining factor is moisture, which may be controlled by adhering to sound construction practices discussed in this program. Bottom Line: No Moisture Means No Mold or Mildew Vapor Diffusion What Is Vapor Diffusion? The Process by which water vapor migrates through a wall system and it s components such as gypsum, concrete, insulation and paint. Warm migrates toward cold When heating, warm indoor air migrates toward a cold exterior. When cooling, warm exterior air migrates towards an air conditioned interior. More moisture moves towards less moisture. Nature tries to equalize. Warmer air is able to hold more moisture than cooler air. The vapor drive will typically be from high concentrations to low concentrations. Each components of the wall system has a perm rating The International Building Code says that a material with a perm rating of 1.0 or less is a vapor retarder. Vapor Diffusion Each components of the wall system has a perm rating The International Building Code says that a material with a perm rating of 1.0 or less is a vapor retarder. EPS Material M Perms Perm-in. Concrete _ 3.2 Wood _ 0.4 5.4 Extruded Polystyrene _ 1.1 Expanded Polystyrene _ 2.0 5.8 Polyisocyanurate _ 0.02 6.6 Glass fiber batt _ 120 Kraft batt 1 Gypsum wallboard (0.375 50 in) Polyethylene (6 mil) 0.06 XPS ISO 10
Introduction Zone # Description U.S. Cities 1A, 2A, 3A Warm, humid Miami, Houston 2B Warm, dry Phoenix SEVERE COLD 3A, 4A Mixed, humid Memphis, Baltimore 3B, 3C, 4B Mixed, dry El Paso, San Francisco 4C Cool, marine Salem, Oregon 5A, 6A Cool, humid Chicago 5B, 6B Cold, dry Boise, ID 7 Very cold Duluth, MN 8 Subarctic Fairbanks, AK HOT DRY COLD MIXED HUMID HOT HUMID Vapor Diffusion Warm Inside Cold Outside In a cold/mixed climate, the wall will cool from the outside, through thermally conductive sections. Insulation is critical in preventing the warm, moisture laden, interior air from coming in contact with these cold surfaces. These are areas where condensation will occur, especially if the perm rating of the devising material is greater than 1.0. Vapor Diffusion In a hot/mixed climate, it is also common for diffusion to occur from the exterior side of the wall. Not only can wind driven rain be absorbed in the exterior and stored, but high humidity levels can promote moisture migration. Moisture will again diffuse and become condensation, especially if the material perm rating is greater than 1.0. 11
Building Fundamentals While moisture diffusion occurs on a molecular level, moisture movement by exfiltration/infiltration occurs when the outdoor/indoor air physically moves through commonly occurring penetrations, unsealed joints, joints in the exterior vapor/air barrier, window openings, flashings, etc. The potential for vapor movement buy exfiltration/infiltration is many times higher than diffusion due to the slowness of the diffusion process. Air Exfiltration Air Exfiltration: The outward movement of air, not through materials, but through gaps, openings, joints in these materials. The driving force for exfiltration is air pressure differences. The latter can be caused by stack effects, wind effects, etc. EXTERIOR INTERIOR Air Infiltration Air Infiltration The inward movement of air, not through materials, but through gaps, openings, joints in these materials. Like exfiltration, the driving force for infiltration is air pressure difference, resulting from stack effects, wind effects, and building depressurization from ventilation. EXTERIOR INTERIOR 12
Air Management How does air infiltrate or exfiltrate the envelope? 5% to 20% of air leakage in buildings occurs at doors and windows. 20% to 50% of air leakage occurs through the walls. Material Average leakage, cfm/ft 2 of surface at 0.3 in. H 2 O Solid precast concrete wall No measurable leakage Aluminum foil vapor barrier No measurable leakage Extruded polystyrene insulation No measurable leakage Closed cell spray foam insulation 0.0002 ½ fibreboard sheathing 0.31 Breather type building membranes 0.0022 0.71 Uncoated brick wall 0.31 Uncoated concrete block 0.41 1 expanded polystyrene 0.93 Air Management Vapor Diffusion 4x8 sheet of gypsum board interior at 70ºF and 40% RH 1/3 Quart of Water Air Exfiltration / Infiltration 4x8 sheet of gypsum board with a 1in 2 hole interior at 70ºF and 40% RH 30 Quarts of Water Taken from Builder s Guide by Lstibburek, Joseph of Building Science Corporation, Westford, MA, July 2000. Dew Point In order to successfully determine whether any given assembly, under a given set of interior and exterior conditions, has the potential for condensation, you should consider the Dew Point Based on: The type and position of each component in the wall assembly. The inside temperature and relative humidity The outside temperature and relative humidity The point when water in a gas form (vapor) changes to liquid 13
Dew Point Cold Medium Warm Warm air can contain more water vapor than cold air. Relative humidity (Rh) being how much moisture is contained in a parcel of air of that temperature compared to how much moisture could be held by that same parcel of air. When you change the air temperature, you change the size of the container. Dew Point 70 F 30% RH 70 F 50% RH Dewpoint: 37.3 F 50.5 F Dew Point 70 F 50% RH 90 F 10% RH Dewpoint: 50.5 F 26.9 F 14
Dew Point TODAY S WEATHER IN DALLAS 6 a.m. 3 p.m. 56 F 58% RH 69 F 60% RH Dewpoint: 43.0 F 55.0 F Dew Point A dew-point calculation chart shows all. % Relative Humidity 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 Temperature F 110 110 108 106 104 102 100 98 95 93 90 87 84 80 76 72 65 60 51 41 105 105 103 101 99 97 95 93 91 88 85 83 80 76 72 67 62 55 47 37 100 100 99 97 95 93 91 89 86 84 81 78 75 71 67 63 58 52 44 32 95 95 93 92 90 88 86 84 81 79 76 73 70 67 63 59 54 48 40 32 90 90 88 87 85 83 81 79 76 74 71 68 65 62 59 54 49 43 36 32 85 85 83 81 80 78 76 74 72 69 67 64 61 58 54 50 45 38 32 80 80 78 77 75 73 71 69 67 65 62 59 56 53 50 45 40 35 32 75 75 73 72 70 68 66 64 62 60 58 55 52 49 45 41 36 32 70 70 68 67 65 63 61 59 57 55 53 50 47 44 40 36 32 65 65 63 62 60 59 57 55 53 50 48 45 42 40 36 32 60 60 58 57 55 53 52 50 48 45 43 41 38 35 32 55 55 53 52 50 49 47 45 43 40 38 36 33 32 50 50 48 46 45 44 42 40 38 36 34 32 45 45 43 42 40 39 37 35 33 32 40 40 39 37 35 34 32 35 35 34 32 32 32 69 Temp + 60% RH = 55 Dew-Point Temp Dew Point In order to eliminate condensation, the following actions should be taken Increase surface temperature or reduce airborne moisture Install a vapor retarder on the inside of the batt-insulation in cold climates. Install a vapor retarder on the outside of batt-insulation in warm climates. Prevent or reduce air infiltration Prevent or reduce rainwater leakage Pressurize or depressurize the building depending on the climate, so as to prevent warm, moist air from entering the building envelope. Use integral insulation with appropriate perm rating. 15
Dew Point Much like a can insulator, a layer of rigid insulation serves to reduce the potential for dew-point condensation. Create a Thermal and Moisture Barrier There is no cavity for moisture to collect. Any dew point occurs in the foam or exterior wythe, not within a wall cavity, so there is no condensation. There are no thermal bridges in the wall. The walls are resistant to moisture Insulation does not support the growth of mold and mildew. Edge to edge detailing prevents vapor diffusion and air infiltration. Create a Thermal and Moisture Barrier 90 Corner Typical Panel to Panel Parapet Typical Footing 45 Corner 16
Create a Thermal and Moisture Barrier Minimal Maintenance for 20 years or longer Architectural maintenance free exterior Caulking every 20 years +/- Interior exposed concrete surface Periodic interior painting Summary H * A * M Heat (Energy Efficiency) Air (Infiltration/Exfiltration) Moisture (Dew Point Control) Summary Mold Mitigation Fungal spores Oxygen Optimal temperatures Nutrients Moisture 17
Summary Condensation Minimize mold and mildew Improve Indoor Air Quality; properly evaluate, or eliminate, cavity construction in the building shell. Air Infiltration & Exfiltration Seal those gaps and cracks! We ve discussed how through diffusion and air infiltration/exfiltration, water vapor can work it s way through a wall. Air leakage (infiltration) accounts for a significant amount of moisture entering the building/building envelope. Summary Dew Point Control Practice positive dew point control through the use of insulation materials Eliminate dew point condensation issues through vapor diffusion and ensure the building envelope is sealed from unwanted air movement. Summary Continuous Insulation (ci) & Sealing Continuous, edge-to-edge, closed cell, rigid foam board insulations will do the most to control moisture and provide the best thermal performance characteristics for all building enclosure types. Joints sealed to the building use and type are critical. 18
Summary Always the same questions How do we navigate the myriad of building and energy codes? What codes are applicable to my project today? What minimum codes are required when building LEED certified buildings? Thank you! Questions? For more information visit www.pci.org Email Brian Miller at bmiller@pci.org 19