8/14/2015. Course Description. Course Objectives AIR, WATER, AND MOISTURE MANAGEMENT IN LIGHT COMMERCIAL BUILDING ENVELOPES

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1 AIR, WATER, AND MOISTURE MANAGEMENT IN LIGHT COMMERCIAL BUILDING ENVELOPES Traditional and Next Generation Solutions New England Building Officials Education Association Conference October 5-7, 2015 Course Description A dry building is a durable building. And a dry building depends on design and construction practices that keep moisture in all its forms solid and vapor out. Moisture enters a building in many ways and can't always find it's way out. This course explains how moisture enters a building envelope, how conventional moisture management methods often fail, and illustrates the latest practices for keeping moisture out of the building envelope, and how to provide a drainage plane for when it does. Course Objectives Identify the four Ds of water management and how they affect the building envelope Explain the physics of air and moisture movement through the building enclosure, and give an example of solar driven moisture Discuss four pitfalls with how today's buildings are being designed and built to protect against air and moisture Describe three alternative moisture and air barrier design solutions to increase the costeffectiveness and sustainability of the structure 1

2 Course Outline Section 1 Moisture Management in Buildings Section 2 Air Leakage and Thermal Performance Section 3 Vapor Management Section 4 Pitfalls of Today s Control Methods Section 5 Alternative Solutions Section 6 Conclusion Introduction A dry building is a durable building. Yet properly managing the movement of air and moisture across the building envelope has long bedeviled architects and builders. To effectively control the indoor environment for energy savings and occupant comfort, today s construction practices are moving to a tighter building envelope. Introduction In a tight building Heating and cooling efficiencies can be maximized Ventilation system can manage moisture levels and indoor air quality High performance rewarded by LEED and other green building programs 2

3 SECTION 1 Moisture is single greatest threat to a building s durability and long-term performance. Rot Mold Mildew Corrosion Maintenance problems Poor indoor air quality Building system failure Liability issues for building designers and owners Moisture is transmitted through: Gross or liquid water Air Vapor Water exists in two phases: Liquid Gas When water is a gas or vapor, the molecules are free to move about they run free IBC Section 1403, Section

4 Moisture is transmitted through: Gross or liquid water Air Vapor Water exists in two phases: Liquid Gas When water is a gas or vapor, the molecules are free to move about they run free. Moisture is transmitted through: Gross or liquid water Air Vapor Water exists in two phases: Liquid Gas When water is a gas or vapor, the molecules are free to move about they run free. Bulk water Driven primarily by gravity and also by capillary action, or wicking. Moisture vapor Diffuses into and through a wall: From high vapor concentration to low vapor concentration From the warm side of a wall to the cooler side 4

5 Greatest risk Liquid water carried into a building through holes and cracks Moderate risk Air carrying water vapor Lowest risk Vapor, which moves through the air Four key strategies, known as the Four Ds, keep moisture from getting into a building. The Four D's Deflection Drainage Drying Durability The Four Ds have two objectives: 1. Prevent moisture from getting into the structure in the first place (deflection) 2. Any moisture that does get into the structure must be managed as quickly and thoroughly as possible (draining, drying, and durability) 5

6 Deflection: Keep rain water off wall and other entry points. Panel Cladding System Lap Siding Masonry Veneers Drainage: Water must be able to drain off the face of building. Drainage Rainscreen & Ventilation Drainage Effective drainage within a wall assembly includes: Screen or cladding Primary water shed layer (for deflection) Secondary water resistive barrier Drainage plane, or a water repellent plane Weep holes or flashing at areas of interruption and at the base 6

7 Drainage Water can be wicked up through the exterior cladding Drainage mats create a clear, drainable space Brick veneer should be back ventilated 2009/2012 IBC Section Drying Water that cannot be drained immediately should be dried as quickly as possible principally through diffusion and ventilation. The drying potential of wall affected by: Evaporation rate from surfaces Vapor movement by diffusion or air leakage Drainage by gravity and convection Air movement Drying When the wetting rate exceeds the drying rate, problems occur and accumulate. What maximizes drying potential? Air gaps Products that don t absorb water Products that let liquid water readily pass through 7

8 Durability Most mistakes occur under the drainage category with the use of improper flashing, ineffective water resistive barriers, and noncontinuous air barriers. By this time, many designers realize that avoiding vapor barriers is important IBC Section SECTION 2 Uncontrolled air flow: Introduces moisture that can cause rot and mold Can increase energy use Can increase indoor air quality problems Sheet Applied WRB 8

9 Proper sealing between wall assembly components prevents unwanted air movement that washes through insulation and degrades the effective R-value. Three types of air flow: 1. Diffusion 2. Orifice flow 3. Channel flow Concentrated Condensation Vapor Barrier Channel Flow Diffuse Flow Orifice Flow Building Envelope A System of Many Components Exterior walls Foundation Roof Windows and doors Penetrations Interfaces Sub systems HVAC Plumbing and electrical systems Activities of building occupants Building Envelope A System of Many No one product can control air leakage Air tightness is a function of the entire building envelope Everything must work together to achieve effective air tightness The airtightness of a building envelope cannot be overestimated. A building s energy efficiency, occupant comfort and sustainability quotient depend on it. 9

10 Convective Loops Today, the most commonly used insulation is still fiberglass batts, which offers a relatively low cost for the function it performs. : Convective Looping Sheet applied WRB Integrated WRB and panel 5 mph wind: Effective R-Value Reduced by 50% 5 mph wind: Effective R-Value Unchanged 10

11 Preventing Air Flow Through the Wall Key factors: Durability Strength Impermeability Sufficient stiffness to allow adhesion Air barrier assembly testing standard (ASTM E 1677 or 2357) Testing for Air Leaks A blower door pulls air out of the house, lowering the air pressure inside The higher outside air pressure then flows in through all unsealed cracks and openings Air leaking into the house from outside can be detected using a smoke pencil Use a calibrated door with gauges that measure the amount of air pulled out of the structure by the fan The calibrated blower door's data determine the amount of air leakage and the effectiveness of air-sealing job 11

12 Testing for Air Leaks Thermography, or infrared scanning, detects thermal defects and air leakage in building envelopes in conjunction with a blower door test. To Improve Air Tightness Most common: Tapes Gaskets Caulks Spray Foam materials 2009 and 2012 IECC require joints/penetrations be sealed with compatible materials Building wraps and sheet applied materials Pros: Can help decrease air leaking provided all seams, edges and details are sealed, and that it is caulked at the bottom Cons: Sometimes susceptible to ripping or tearing Must be handled carefully 12

13 Peel n Stick Air Barriers for Roof Pros: Considered a superior option for ice and water barriers Can be a first layer on potentially problematic areas Can be installed on the entire roof if it is low slope or flat Cons: The adhesive is temperature-sensitive until securely bonded to a dry surface Sometimes slippery, and unsafe to walk on directly after application Taped wall sheathing panels Taped sheathing panels form a continuous protective air barrier Significantly reduce air leakage through walls or roofs Lower air changes per hour Help optimize R-value Save energy Meet stringent codes and certifications SECTION 3 Vapor Management 13

14 Vapor Management Water as vapor causes problems when it becomes trapped in an assembly and turns to liquid (condensation) Water vapor moves by only two mechanisms air transport and vapor diffusion Vapor Management Hot air holds more moisture than cold air Air currents could carry significant amount of moisture into the building enclosure AIR-TRANSPORTED MOISTURE VAPOR DIFFUSION Vapor Management Dew Point and Condensation Considerations Graphic with R sheathing and graphic with zip panel with foam on top. Discussion: Using continuous insulation as one strategy to controlling moisture in a wall ( dew point and condensation) Warm wall Dew point is a temperature. See Allan s presentation on styrofoam cup and regular cup and condensation. 14

15 Vapor Management Integrated WRB and panel Sheet applied WRB Wood Perm rating-=2-3, Water resistive barrier overlay perms= Moisture Carried Moisture Carried by Vapor Drive by Air Infiltration > 24 ounces > 228 gallon Moisture Carried Moisture Carried by Vapor Drive by Air Infiltration > 8 ounces > 1 gallon Thermal Resistance and Dew Point Framing Structural Panel Framing Structural Panel WRB WRB Sheetrock Cavity Insulation Sheetrock Cavity Insulation Rigid insulationinterior to sheathing Rigid insulationexterior to sheathing Vapor Management Sheet applied WRB Materials which retard water vapor flow are said to be impermeable Materials which allow water vapor to pass through them are said to be permeable Moisture Carried Moisture Carried by Vapor Drive by Air Infiltration > 8 ounces > 1 gallon 15

16 Vapor Management Solar Vapor Drive A wet surface heated by the sun develops a high vapor pressure, drives moisture into absorbent materials. Vapor Management DO: Exterior walls must be completely sealed to prevent vapor or air from entering, which is not an easy task. DON'T: Designers should never specify a material on the interior that will trap moisture in the wall, like poly or vinyl wallpaper. SECTION 4 Pitfalls of Conventional Moisture Control Methods 16

17 Pitfalls of Conventional Moisture Control Methods Water-Resistive Barrier A thin membrane intended to resist liquid water that has penetrated behind the exterior cladding Proper installation is critical Water must remain outside of the protective wrap May improve performance by acting as a secondary moisture drainage plane Pitfalls of Conventional Moisture Control Methods Roll or Spray-On Products Difficult to achieve the proper mil consistency Multiple layers of coating are required Cure time makes for a slower installation process Pitfalls of Conventional Moisture Control Methods Grade D Building Paper Does not function well as air barrier/retarder Tears easily, particularly if left exposed Can be difficult to install in windy conditions 17

18 Pitfalls of Conventional Moisture Control Methods Sheet Applied WRB All seams, holes, and penetrations in sheet applied WRB s must be properly sealed (including the bottom) Tears easily if left exposed Difficult to install in windy conditions There is poor adhesion of flashing material and tape Complex and ever-changing flashing, repair and installation details Pitfalls of Conventional Moisture Control Methods Issues with sheet applied WRB s: Building wrap tucked into the building (reverse shingling) Improperly flashed penetrations Flashing tape that doesn t stick Pitfalls of Conventional Moisture Control Methods Direct applied stone or three-coat stucco over wood based sheathing: Wood sheathing First layer of WRB (drain plane) Additional layer of WRB Metal Lath Brown coat (bond break) Scratch coat Finish coat 18

19 Pitfalls of Conventional Moisture Control Methods Dried In Roof Creating a sealed roof deck Allows mechanical trades to start work Felt can blow off Two trades involved Felt difficult to install In a National Association of Home Builders survey, nearly one quarter (23 percent) of respondents cited absence of or damaged felt as a problem. SECTION 5 Alternative Solutions Alternative Solutions Extruded Polystyrene Sheathing Lightweight alternative Not a structural panel No nail holding strength Easily punctured The vapor permeance less than 3 Has insulating properties Some types can be installed as a water resistive barrier and air retarder with special detailing Seams must be taped 19

20 Alternative Solutions Roll- or Sprayed-On Water Resistive Barrier May require special inspection Specific requirements for: Temperature range Mil thickness Substrate differences Dry time Multiple coats? Consistency difficult to achieve Alternative Solutions OSB Panel with Integrated WRB/Air Barrier Structural panel with an integrated moisture/air barrier Continuous water and air barrier After seam taping the code required WRB AND air barrier is established All systems require proper detailing Conclusion Properly constructing a building envelope for optimum moisture and air leakage control leads to sustainable, energy efficient buildings As technology advances, buildings systems become more effective With all systems, you must comply with evaluation reports and installation instructions. The devil is in the details! 20

21 Thank You Thank you for participating This concludes the Huber Engineered Woods Continuing Education Program Air, Water & Moisture management in Light Commercial Building Envelopes For Technical questions: ext or 21