Designing High Performance Walls for Cold Climates (like ours)

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1 Designing High Performance Walls for Cold Climates (like ours) Learning Objectives: Attendees will may be able to: o Outline the major building science topics that must be considered when designing a highly insulated envelope. o Categorize the major options and trade-offs for insulating high R- value frame wall assemblies. o Explain the basics of hygrothermal modeling and the need for it. o Recognize assembly characteristics that affect moisture risk. Dave Bryan AIA, LEED AP Third Level Design Rolf Jacobson LEED AP, CPHC Skandia Design & Consulting 100% Estimated Energy Use Reduction relative to the 2006 Energy Code (ASHRAE & IECC 2006) 90% 80% 70% 60% 50% 40% 30% 20% 10% 2012 IECC adoption in MN 0% Architecture Target w/o 15% PV ASHRAE 90.1 & IECC Typical reductions from: Mitigating CO2 Emissions from Energy Use in the World's Buildings, Urge-Vorsatz, Harvey, Mirasagedis, Levine,

2 R value Requirements for Wall Assemblies Climate Zone 6 How do we achieve R30 plus walls? Previous MN ASHRAE Increase from IECC 2012 Commercial : Energy Code IECC 2012 IECC 2006 Prescriptive Walls, metal-framed R11.9 R % R ci Walls, metal-framed, R R % R ci Walls, wood-framed R11.2 R % R ci or R ci Previous MN Minnesota 2015 Increase from Minnesota Residential : Energy Code Residential Energy Code IECC 2006 Prescriptive Walls, metal-framed R15.6 R % R ci, etc. Walls, wood-framed R15.6 R % R20, R ci U and R values are clear wall numbers Generic Wall Components & Functions Moisture Movement Mechanisms Higher air pressure Lower air pressure Air flow through visible cracks and holes Water vapor is carried by the air Higher water vapor concentration Lower water vapor concentration No air flow Water vapor flow through tiny pores Control with Air Barrier Small holes & seams must be sealed. Continuity important Control with Vapor Retarder Small holes & seams not too important if there is a good air barrier Both Air Barrier and Vapor Retarder are important from: Insulations, Sheathings and Vapor Diffusion Retarders, Building Science Corporation

3 Forces Creating Air Movement Convective Air Loops Reduce Effective Insulation Value From Air Leakage Control in Multi-Unit Residential Buildings, RDH Building Science Corporation, BSD-011 Thermal Control Alternative Air Barrier Locations Air Barrier Strategies Interior 1. Sealed polyethylene Approach Caulk polyethylene vapor barrier to framing at perimeter and joints Seal at electrical boxes and other penetrations Maintaining continuity between floors and at partition walls is difficult Unsuitable for taller buildings because of wind loads and lack of support by cavity insulation Easily damaged during construction 2. Airtight Drywall Approach Caulk gypsum board to framing or vapor barrier at perimeter and joints Seal at electrical boxes and other penetrations Maintaining continuity between floors and at partition walls is difficult Accessible and easy to repair during blower door testing 3. Sealing sheathing from inside stud cavity Closed cell or open cell spray foam insulation Provides both insulation and air barrier Airtightness is susceptible to building movement and long term foam shrinkage Spray foam cannot seal small gaps at framing Flexible spray sealants can seal gaps up to 3/8 without using backer rod To seal leaks, blower door testing can be performed without drywall and cavity insulation From Building Science Corp, BSI-084,40 Years of Air Barriers Knauf Ecoseal Plus 3

4 Air Barrier Strategies Exterior 4. Taped synthetic house wrap sheeting Difficult to avoid wind damage to mechanically attached sheeting during construction If not sandwiched between sheathing and cladding or exterior insulation, may pump in wind. Possible damage by brick ties Not recommended for high rise use Relatively inexpensive 5. Taped exterior insulation Compatible tapes are available Concerns about long-term adhesion with insulation movement and aging Is a water barrier still needed? 6. Adhesive-backed weather/air barriers Vapor permeable membranes are available Resistant to fastener damage Relatively expensive 7. Liquid or fluid-applied air/weather barriers Includes material to bridge sheathing joints Vapor permeable coatings are available Compatible with EIFS Relatively expensive 8. Sealed sheathing joints Compatible sealants and tapes are available Less expensive than liquid/fluid-applied or adhesive-backed systems Need additional water barrier unless sheathing is coated for water resistance From a MN BEC presentation by Graham Finch at RDH Worst Case Air Leakage Scenario Window Location and Control Layers Must Be Coordinated 1. air permeable cavity insulation 2. major vapor retarder and/or air barrier failure 3. moist room air reaches cold, moisture sensitive sheathing Low Damage Potential High Damage Potential Fraunhofer Institute from Thermal Bridges Redux, Building Science Corp

5 Blower Door Infiltration Targets Description Residential Commercial 50 Pascals CFM/Sq Ft 75 Pascals Typical Existing Building 24 (6 since1993) 1.40 Energy Code (testing is optional) Army Corps of Engineers.25 Readily achieved with reasonable care Reliably achieved with significant effort 1.5 Passive House 0.6 Vapor Permeability of Selected Building Materials Class 1 Vapor Barriers Class 2 Vapor Retarders Class 3 Vapor Retarders 0 to.1 perms.1 to 1 perms 1 to 10 perms Polyethylene Sheet Vapor Barrier Paint Latex Paint Aluminum Foil Oil-based Paint, 3 coats Oil-based Paint, primer +1coat most Bituminous Sheet Closed-cell Polyurethane Closed-cell Polyurethane Materials spray foam, thicker than 2 spray foam, less than 1 Vinyl Wall Covering, Extruded Polystyrene, Extruded Polystyrene, un-perforated unfaced, thicker than 1 unfaced, less than 1 Hot Asphalt Roofing Kraft Paper (nominal) Kraft Paper (NAHB measured) Smart Vapor Retarders Open-cell Polyurethane (Membrain, Intello) spray foam (Icynene) Residential equivalent of.4 cfm/ft2 at 75 Pa ~ 3 to 5 air changes/hour at 50 Pa Building codes generally require Class I or Class II vapor retarders for Climate Zones 5 through 8 Smart Vapor Retarder Performance Diameter of the circle is proportional to water vapor content of the air Certainteed 5

6 Differential between Interior and Exterior Dewpoints JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Indoor Air: 40% winter RH to 60% summer RH Indoor Air: 40% winter RH to 50% summer RH Minneapolis, MN Miami, Fl From a MN BEC presentation by Graham Finch at RDH 11/13/ Extruded polystyrene, continuous Expanded polystyrene, continuous Mineral Wool, 8 lbs/ft3, continuous Polyisocyanurate, continuous Closed cell spray foam, wood studs Fiberglass batt, wood studs Cellulose, blown, wood studs Fiberglass, sprayed, wood studs Closed cell spray foam, metal studs Fiberglass batt, metal studs Cellulose, blown, metal studs Fiberglass, sprayed, metal studs Dewpoint, F. $0.55 Relative Cost Effectiveness of Wall Insulation $0.50 $0.45 $0.40 $0.35 $0.30 $0.25 $0.20 $0.15 $0.10 $0.05 Installed Cost per Effective R value Greenhouse Gas Savings 60 % of Savings Extruded Polystyrene 37 % of Savings Closed Cell Polyurethane Spray Foam Open Cell Polyurethane Spray Foam Polyisocyanurate Expanded Polystyrene Mineral Wool Fiberglass Cellulose $0.00 Exterior Insulation Insulation Between and Wood Assembly Studs Type Between Metal Studs 16 Greenhouse Gas Savings and Emissions for Exterior Insulation in Climate Zone Kg of Greenhouse Gas, 50 yr total Savings are for reducing natural gas use by adding R10 insulation to a base R15 wall Based on Total Climatic Impact of Insulation, David White, 2011

7 General Approaches to Frame Wall Insulation What can we achieve with only stud cavity insulation? What can we achieve with only stud cavity insulation? Wood studs, 2x8, 16 o.c. Nominal Correction Actual Insulation Type R-value Factor R-value Cavity Insulation 7.25 x R4 /inch = 30.0???? Other Materials Clear Wall R-value?? Metal studs, 1 5/8 x 7.25, 16 o.c Nominal Correction Actual Insulation Type R-value Factor R-value Cavity Insulation 7.25 x R4 /inch = 30.0???? Other Materials Clear Wall R-value?? Advanced Framing Conventional framing with 2x6 s 16 o.c. Framing factor: 25% Clear wall R-value: 17.9 Conventional framing with 2x6 s 24 o.c. Framing factor: 20% Clear wall R-value: 18.3 Advanced framing: Framing factor: 15% Clear wall R-value: 19.0 Less labor, less lumber, higher R-values Building Science Corp, BSI-030 Advanced Framing 7

8 90% Stud Cavity Insulation Effectiveness for full cavity fill, from EZFRAME, California Energy Commission What can we achieve with only stud cavity insulation? Cavity Insulation Effectiveness Factor 80% 70% 60% 50% 40% 30% See ASHRAE 90.1, Tables A3.3 & A3.4 20% Stud Spacing, in. 2x4 wood studs 2x6 wood studs 2x8 wood studs 2x4 metal studs, 20 Ga. 2x6 metal studs, 20 Ga. 2x8 metal studs, 20 Ga. Wood studs, 2x8, 16 o.c. Nominal Correction Actual Insulation Type R-value Factor R-value Cavity Insulation 7.25 x R4 /inch = % 24.3 Other Materials Clear Wall R-value 26.9 Metal studs, 1 5/8 x 7.25, 16 o.c Nominal Correction Actual Insulation Type R-value Factor R-value Cavity Insulation 7.25 x R4 /inch = % 11.1 Other Materials Clear Wall R-value 13.6 How do we design energy efficient building enclosures that avoid problems with mold, rot and corrosion? How we used to do it: Consider examples of local buildings Consult best practices checklist Comply with building codes Guess the rest! 8

9 Condensation Analysis Shortcomings Requires guessing an appropriate static outdoor temperature Does not address: o Moisture storage capacity or permeability of materials o Seasonal variation in indoor and outdoor temperature and humidity o Time dependent nature of wetting and drying cycles o Driving rain penetration o Relative tightness or leakiness of assemblies o Vapor barrier type o Solar radiation and surface orientation o Condensation versus frost Assumes implicitly that damage does not occur until liquid water is present Damage Threshold Criteria Identify moisture sensitive materials and critical components Structural damage of wood products: o Limit moisture content of wood products to 18% peak (80% to 85% R.H.) Structural damage of gypsum products: o Limit moisture content of fiberglass-faced gypsum to 90% to 95% R.H. Corrosion of metals: o Keep the surface of metals < 80% R.H. for any 30 day period (unless specific material information is available) Mold Growth (ASHRAE 160): o 30 day running surface temp average < 80% RH when between 41 and 104 F. Corrosion Rates vs RH, Harriman, 2003 Sorption Curve for Common Building Materials 9

10 HYGROTHERMAL MODELING with WUFI An analytical tool for designing building assemblies to: o o Control moisture Reduce the risk of mold, rot and corrosion Allows fine-tuning assemblies for longevity and cost-effectiveness Allows sensitivity analysis to determine critical variables: o Vapor retarder type o Insulation quantity, type and location o Sheathing type o Air-tightness of assemblies o Water and Air barrier permeability o Natural ventilation of wall and roof cavities o Interior relative humidity Wind-Driven Rain and Building Envelopes Perfect building assemblies exist only on paper Most wall claddings and many types of roof claddings leak Moisture-tolerant enclosures must be designed to deal with water that penetrates the cladding ASHRAE Standard 160 Criteria for Moisture Control in Buildings requires walls to withstand 1% of wind-driven rain penetrating the cladding Modeled and Measured Drainage, Storage and Drying behind Cladding Systems, Straube,

11 Exterior Climate Driving Rain Varies Tremendously by Region Zone 6 Zone 6 Zone 5 5/8 gypsum board with latex paint Minneapolis Montpelier Boston Example of WUFI Wall Section Input Interior Climate Fraunhofer Institute, Holzkirchen, Germany: Building Mold and Fungi Studies 11

12 Good RH/Temp Data Points Bad RH/Temp Data Points WUFI Limitations Initial construction moisture in interior gypsum board dries gradually over a three year cycle Interior gypsum board annually cycles back into the mold growth danger zone Time Sequence of Data Points: yellow to green to black Results are sensitive to material properties o The requisite material properties are very detailed o Complete data rarely available from manufacturers o Must use standard WUFI library and modify as needed Results are very sensitive to indoor relative humidity o Varies by building use, airtightness, climate and user activity No local active group or third party operation & reference manual o Must rely on personal research of available literature and WUFI forums Materials meeting the same specifications can exhibit significant variation in physical properties (i.e. brick) Most assemblies aren t homogeneous and the WUFI version in common use is one-dimensional WUFI 2D Stud Wall Comparison Wood Stud Wall Metal Stud Wall WUFI 1D center of sheathing Same both cases What can we achieve with only stud cavity insulation? Wood studs, 2x8, 16 o.c. Nominal Correction Actual Insulation Type R-value Factor R-value Cavity Insulation 7.25 x R4 /inch = % 24.3 Other Materials Clear Wall R-value 26.9 Metal studs, 1 5/8 x 7.25, 16 o.c Nominal Correction Actual Insulation Type R-value Factor R-value Cavity Insulation 7.25 x R4 /inch = % 11.1 Other Materials Clear Wall R-value

13 Legacy 2x8 Wall fiberglass insulation, plywood sheathing, polyethylene vapor barrier, 20% winter RH, poor air barrier Legacy 2x8 Wall fiberglass insulation, plywood sheathing, polyethylene vapor barrier, 20% winter RH, poor air barrier Sheathing moisture content Sheathing relative humidity and temperature 2x8 Wall current conditions fiberglass insulation, plywood sheathing, polyethylene vapor barrier Double Stud Wall High R with no foam Could also be behind gyp.bd. Air barrier location? For R30 clear wall: 3 gap for wood studs 4 gap for steel studs 40% interior winter RH and poor air barrier 40% interior winter RH and residential code-compliant barrier Building America High R Walls Case Study Analysis 13

14 Double Stud Wall High R with no foam Hollis, New Hampshire Montessori School Could also be behind gyp.bd. Air barrier location? For R30 clear wall: 3 gap for wood studs 4 gap for steel studs Why? Lower GWP Fewer air pollutants No cantilevered cladding No thermal bridge at studs But: Uses extra floorspace No thermal break at floors Need good moisture control Building America High R Walls Case Study Analysis 12 thick double stud walls with dense pack cellulose, R41. 15% energy consumption of comparable code-compliant schools. Meets Passive House standards. 10% additional construction costs with 3 year payback. Double Stud Wall High R with no foam Double Wall Sheathing Conditions for 9 cellulose, Tyvek, fiberboard sheathing, smart vapor retarder, unvented For R30 clear wall: 3 gap for wood studs 4 gap for steel studs 40% to 60% interior RH 9 dense pack cellulose Smart vapor retarder Fiberboard sheathing 3 50 Pa infiltration Tyvek water barrier Fiber cement siding ASHRAE 160: 30 day mold criteria failure hours/year: 3933 (45% of hours) Building America High R Walls Case Study Analysis 14

15 WUFI allows simulation of the effectiveness of Naturally-Ventilated Wall and Roof Cavities Double Wall Sheathing Conditions for 9 cellulose, Tyvek, fiberboard sheathing, smart vapor retarder, vented ASHRAE 160: 30 day mold criteria failure hours/year: 355 (4.1% of hours) Modeled and Measured Drainage, Storage and Drying behind Cladding Systems, Straube, 2007 Foam insulation or mineral wool board Exterior Foam Insulation Fire Considerations Perfect Wall NFPA , Evaluation of Flammability Characteristics of Exterior, Nonloadbearing Wall Assemblies Containing Combustible Components (IBC ). Applies to non combustible buildings (Type I, II, III, IV) Typically this means buildings larger than 25,000 square feet Requires expensive fire testing of the exact assembly proposed in the design Some foam insulation manufactures have tested assemblies Dow and Hunter, for example Must follow manufacturer s details XPS and EPS require fire blocking around openings and don t play well with metal cladding. Polyisocyanurate is more forgiving. Also applies to WRB and combustible cladding in buildings over 40 feet tall high pressure laminates, fiber reinforced polymers, metal composites 15

16 Vertical Furring Strips on Rigid Insulation Design an R30 metal stud wall (2x6 s,16 o.c.) Case 1: Assume stud cavity has no insulation Nominal Correction Actual Poliso (R5.4) Insulation Type R-value Factor R-value Thickness Stud Air Space Other Materials Continuous Exterior Insulation ~5 (too thick?) Total Wall R-value 30.0 Alternative: 8 thick EPS (expanded polystyrene) SIP panels EIFS: 4 max. expanded polystyrene = ~ R18 (not compliant with residential code) Align furring strips with studs Pros: o Thermal bridging of insulation by fasteners only o Cost effective o Provides drainage and cladding support o Can be metal or wood o Offers the opportunity to ventilate the furring cavity Cons: o Limitations to insulation thickness defined by cladding system o Not suitable for heavy cladding o Need horizontal furring strips for vertical cladding systems drainage? The Actual R-value is the clear wall R-value for this assembly Image by BSC Corp. Design an R30 metal stud wall (2x6 s,16 o.c.) for light cladding Case 1: Assume stud cavity is filled with fiberglass insulation Nominal Correction Actual Poliso (R5.4) Insulation Type R-value Factor R-value Thickness Fiberglass Cavity Insulation 21.0???? Other Materials Continuous Exterior Insulation? 1.0?? Total Wall R-value 30.0 Thickness limitations are greater with higher wind loads, heavier claddings and metal studs The Actual R-value is the clear wall R-value for this assembly 16

17 Design an R30 metal stud wall (2x6 s,16 o.c.) for light cladding Case 1: Assume stud cavity is filled with fiberglass insulation Alternative Assemblies for Rmin = 30 Base Wall Materials R = 2.5 R21 Fiberglass (2x6) x.37 R = x R5.4 Polyisocyanurate R = 18.9 Cost /SF per actual R = $0.21 Total = 29.2 Nominal Correction Actual Poliso (R5.4) Insulation Type R-value Factor R-value Thickness Fiberglass Cavity Insulation Other Materials Continuous Exterior Insulation Total Wall R-value 30.0 Note: if the studs were wood, the framing correction factor would be ~.8 and only about 2 of exterior insulation would be needed Base Wall Materials R = 2.5 R13 Fiberglass (2x6) x.37 R = x R5.4 Polyisocyanurate R = 21.6 Cost /SF per actual R = $0.20 Total = 28.9 Base Wall Materials R = 2.5 No Cavity Insulation (2x6) R = x R5.4 Polyisocyanurate R = 27.0 Cost /SF per actual R = $0.22 Total = 30.3 Costs include insulation and furring strips For 2 x6 steel studs, 16 o.c. Image by BSC Corp. ` Alternative Assemblies for Rmin = 30 Base Wall Materials R = 2.5 R21 Fiberglass (2x6) x.37 R = x R5.4 Polyisocyanurate R = 18.9 Cost /SF per actual R = $0.21 Total = 29.2 Furred Wall Case 1 Sheathing Conditions for 3.5 fiberglass-faced polyisocyanurate, 6 fiberglass, smart vapor retarder Base Wall Materials R = 2.5 R13 Fiberglass (2x6) x.37 R = x R5.4 Polyisocyanurate R = 21.6 Cost /SF per actual R = $0.20 Total = 28.9 Base Wall Materials R = 2.5 No Cavity Insulation (2x6) R = x R5.4 Polyisocyanurate R = 27.0 Cost /SF per actual R = $0.22 Total = 30.3 Costs include insulation and furring strips Image by BSC Corp. 40% to 60% interior RH Smart vapor retarder Fiberglass-faced gypsum sheathing 15 perm water / air barrier Fiber cement siding ASHRAE 160: 30 day mold criteria failure hours/year: 2180 (25% of hours) Rout / Rin ~.8 ` 17

18 Furred Wall Case 2 Sheathing Conditions for 4 fiberglass-faced polyisocyanurate, 3.5 fiberglass, smart vapor retarder Furred Wall Case 1 Sheathing Conditions for 3.5 fiberglass-faced polyisocyanurate, 6 fiberglass, polyethylene vapor retarder ASHRAE 160: 30 day mold criteria failure hours/year: (0 hours) ASHRAE 160: 30 day mold criteria failure hours/year: 4887 (56% of hours) Rout / Rin ~ 1.7 Rout / Rin ~.8 Furred Wall Case 1 Sheathing Conditions for 3.5 foil-faced polyisocyanurate, 6 fiberglass, smart vapor retarder ASHRAE 160: 30 day mold criteria failure hours/year: 3461 (40% of hours) Rout / Rin ~.8 Sheathing Peak Relative Humidity 100% 95% 90% 85% 80% 75% 70% 65% 60% 55% Effect of R value Ratio on Wall Moisture Gypsum Sheathing, 15 perm Weather Barrier R30 walls with steel studs or R40 walls with wood studs, Climate Zone 6 Vapor Permeable Exterior Materials Smart vapor retarder Vapor Impermeable Exterior Materials Class 3 vapor retarder 50% R value Outside of Sheathing / R value Inside of Sheathing Foil faced polyisocyanurate exterior insulation, Class 3 vapor retarder Foil faced polyisocyanurate exterior insulation, Smart vapor retarder Fiberglass faced polyisocyanurate exterior insulation, Smart vapor retarder 18

19 100% Effect of R value Ratio on Wall Moisture Plywood Sheathing, 15 perm Weather Barrier R30 walls with steel studs or R40 walls with wood studs, Climate Zone 6 Hybrid Wall Insulation for Heavy Cladding Stucco with Exterior Insulation (Rigid Foam Up to 2 Thick) Sheathing Peak Relative Humidity 95% 90% 85% 80% 75% 70% 65% 60% 55% Smart vapor retarder Vapor Impermeable Exterior Materials Class 3 vapor retarder 50% R value Outside of Sheathing / R value Inside of Sheathing Fiberglass faced polyisocyanurate exterior insulation Smart vapor retarder Foil faced polyisocyanurate exterior insulation Smart vapor retarder Foil faced polyisocyanurate exterior insulation, Class 3 vapor retarder Design an R30 metal stud wall (2x6 s,16 o.c.) for stucco Stucco with Exterior Insulation For Exterior Insulation Greater Than 2 Thick Case 1: Assume stud cavity is filled with fiberglass insulation Nominal Correction Actual Poliso (R5.4) Insulation Type R-value Factor R-value Thickness Fiberglass Cavity Insulation Other Materials Continuous Exterior Insulation Total Wall R-value

20 Exterior Insulation Framing Alternatives Intermittent Z-girts Using Fiberglass Clips Morrison Hershfield From a MN BEC presentation by Graham Finch at RDH From a MN BEC presentation by Graham Finch at RDH 20

21 Exterior Insulation Effectiveness 100% 95% 90% 85% 80% 75% 70% 65% 60% 55% 50% 45% 40% 35% 30% The Real R-value of Exterior Insulated Wall Assemblies Based on ASHRAE 1365-RP 25% Exterior Insulation R-value between Steel Z-girts Wood Studs 16" o.c., 25% framing factor Hoiz. & Vert. Z-girts 24" o.c. Vertical Z-girts 16" o.c. Intermittent Vert. Z-girts 16" o.c. Horizontal Z-girts 24" o.c. Design an R30 metal stud wall (2x6 s,16 o.c.) for stucco Case 1: Assume stud cavity is filled with fiberglass insulation Nominal Correction Actual Poliso (R5.4) Insulation Type R-value Factor R-value Thickness Fiberglass Cavity Insulation Other Materials Continuous Exterior Insulation Total Wall R-value 30.3 The correction factor is for intermittent vertical clips on Z-girts Wall Assemblies Alternatives for R 30 Heavy Cladding with intermittent fiberglass Z-clips Base Wall Materials R = 2.5 R21 Fiberglass (2x6) x.37 R = x R5.4 Polyisocyanurate x.67 R = 20.0 Cost /SF per actual R = $0.34 Total = 30.3 Vinyl Siding 25 yrs EIFS 25 to 50 yrs? Wood Siding 25 to 100 yrs Cement Siding 50 to 100 yrs Simulated Stone 100 yrs or more Stucco 100 yrs or more Brick 100 yrs or more Service Life of Wall Components* Light Cladding with furring and steel screws Base Wall Materials R = 2.5 R21 Fiberglass (2x6) x.37 R = x R5.4 Polyisocyanurate x.90 R = 19.4 Cost /SF per actual R = $0.23 Total = 29.7 For this example, the need for exterior cladding supports: Increases cost/sf per actual R ~ 50% Increases wall assembly costs ~ $3 to $4 / SF Increases building cost ~$1 to $2 / SF?? 83 Brick Ties 25 yrs (hot-dipped galvanized) Brick Ties 50 yrs (epoxy-coated) Brick Ties 100 yrs or more (stainless steel) Flashing 25 yrs (polyethylene) Flashing 25 yrs (galvanized sheet metal) Flashing 100 yrs or more (copper, 18 ga.) Flashing 100 yrs or more (stainless steel, 24 ga.) * A drainage plane is assumed to be present in all cases Excerpted from Increasing the Durability of Building Components, BSD-144, Joe Lstiburek 21

22 Service Life of Wall Components* Water Barriers Non-ventilated & Non-ventilated & Under Rigid Non-backprimed Backprimed Insulation Building Papers 25 yrs 50 yrs 100 yrs or more Housewraps 25 yrs 50 yrs 100 yrs or more Cladding Non-ventilated & Non-ventilated & Ventilated & Non-backprimed Backprimed Backprimed Wood Siding 25 yrs 50 yrs 100 yrs or more Cement Siding 50 yrs 75 yrs 100 yrs or more * A drainage plane is assumed to be present in all cases Apartment building in Margate by Alex Chinneck Excerpted from Increasing the Durability of Building Components, BSD-144, Joe Lstiburek Pro o Low moisture risk o Conceptually simple a vapor impermeable air/water/vapor barrier can be used o Thermal break at framing members and floor line Con o Relatively expensive o Most foam insulation has relatively high environmental impact o Exterior insulation may need to be interrupted with framing to support cladding Pro o Relatively inexpensive if single wall. Can also be high-r double wall o Most cavity insulations have low environmental impact o Simple to construct Con o Increased risk of moisture damage as permeable cavity insulation becomes thicker o Thermal bridging at framing members and floor line for single wall construction o Convective looping more likely with cold sheathing need dense insulation 22

23 Recommendations for Zone 6 Frame Walls Avoid foam insulations with HFC blowing agents: o Use expanded polystyrene, polyisocyanurate, cellulose, mineral wool or fiberglass products instead of closed cell spray foam (ccspf) and extruded polystyrene (XPS). Assume that the wall cladding will not be watertight: o Provide a drainage plane between cladding and water barrier. o It can be as small as 1 mm but 3/8 or thicker is better. o Consider ventilating the drainage gap for additional drying. Ventilate and control indoor moisture to keep RH between 30% and 60%. A Compromise Solution o Intermediate cost o Intermediate environmental impact o Construction difficulty varies o As the R-value ratio of exterior to cavity insulation increases, moisture risk decreases o Thermal bridging is reduced Design walls to dry to the inside as well as the outside when conditions permit: o For interior winter RH greater than 40%, use a Class I vapor retarder like polyethylene. o For normal moisture loads (40% maximum RH in winter), use a smart vapor retarder. Detail a continuous whole building air barrier. Test and seal it during construction. For walls with both exterior insulation and vapor-permeable cavity insulation, pay attention to the (R out / R in) ratio: Higher is Drier. 23