Picking Windows & Glazing Units for Optimal Energy Efficiency in the North

Picking Windows & Glazing Units for Optimal Energy Efficiency in the North NNCA RESIDENTIAL CONSTRUCTION WORKSHOP, YELLOWKNIFE FEB 17, 2016 GRAHAM FINCH, MASC, P.ENG PRINCIPAL, BUILDING SCIENCE RESEARCH SPECIALIST GFINCH@RDH.COM 604-873-1181 Outline Understanding Window Performance Numbers & What It All Means Energy Regulations and Available Window Products in Canada s North Picking Optimal Windows for Northern Canadian Homes Balancing Energy and Comfort G.Finch - RDH 1

Why The Focus on Windows? Are a focal architectural and function part of our homes (views, daylighting, aesthetics) Can be one of the biggest components of heat loss in a building (20-50% range) But they can also gain an appreciable amount of heat, which can be good to reduce space-heat loads or it can also be bad and cause overheating and discomfort Picking windows is a learned experience of conflicting priorities and a fairly technical one at that! The Simple Solution to Windows?! G.Finch - RDH 2

How do YOU Pick a Window? Frame & Glazing Considerations Aesthetics, Colour, Look & Feel? Materials? Hardware & Accessories? Technical Performance & Specifications? Thermal Air-tightness Water-resistance Security Condensation Resistance Code Requirements & Other? Picking Frames Frame Material Vinyl Aluminium Wood Fiberglass Hybrid Combinations Dimensions/Thickness Structural Performanace Aesthetics/Colours/Feel Thermal Performance (U-value) Hardware Integration Installation Method (Flange/Rebate) G.Finch - RDH 3

Picking Glass and Glazing Insulated Glazing Units (IGUs) Double/Triple/Quad Glazing Inert Gas Fill (Air, Argon, Xenon, Krypton) Aesthetics Colour (Clear, Green, Blue, Grey etc.) Clarity (Visible Light Transmission, VLT) Reflection (Inside & Out) Technical Specifications U-value Solar Heat Gain Coefficient (SHGC) ER value UV Blocking Spacer Bars/Edge Seals Insulating Glazing Units (IGUs) With triples add in surfaces 5&6 With quads add in surfaces 7&8 IGU Components: 1. Surface 1 (exterior) 2. Surface 2 (interior side of exterior lite) 3. Surface 3 (exterior side of interior lite) 4. Surface 4 (interior) 5. Low-e coating 6. Edge spacer (separate glass panes) 7. Desiccant (to dry air) 8. Primary edge seal (vapor) 9. Secondary edge seal (structure) Air/gas filled space(s) G.Finch - RDH 4

Triple & Quad IGUs More air/gas spaces = lower (better) IGU U-values Argon minimal cost to add Argon does not leak out through dual seal spacer bars appreciably unless a defect More glass = lower SHGC values Fundamental law with stacking layers of glass together, even clear non-low-e glass Can get good range of SHGC values from low to high for available triple units Low-e coatings typically put on cavity side of inner and outer panes of glass within triples/quads Concerns with glass breakage increases with more layers of glass From experience durability of glass triples/quads is better than thin suspended plastic film systems Free program by LBNL, called WINDOW allows you to design your own IGUs and get all of the optical properties Hard Coat vs. Soft Coat Low-e Coatings Both thin metal films (silver, tin, stainless steel etc.) & antireflective metal-oxide films applied to glass Hard coat (pyrolytic) applied during float process of making glass Tends to result in higher SHGC but lower thermal performance (higher U-values) Soft coat (sputtered) applied to glass anytime Tends to result in lower SHGC but better thermal performance Newer coatings can get best of both worlds high SGHC, high thermal performance Images from PPG G.Finch - RDH 5

How Low-e Coatings Work UV Images from LBNL Aesthetics, Colour, & Reflection G.Finch - RDH 6

Visible Light Transmission Visible Light Transmission (VLT) is the visible light spectrum that is transmitted through the glazing unit Important in day-lighting and glare control Typical range of 30-70%, optimum depends on use of space and window to wall ratio Solar Heat Gain Coefficient (SHGC) SHGC is the % of total solar radiation transmitted as heat-gain through an IGU (window) SHGC of 0.55 = 55% transferred to interior (directly by short wave radiation and indirectly by absorption and long-wave radiation) Remainder is reflected or absorbed and re-radiated back out Too high of SHGC can cause overheating within highly glazed spaces Not high enough SHGC can limit amount of potential free heat gain that may be beneficial in heating climates SHGC for a window includes the frames, hence why operable windows have lower SHGCs overall G.Finch - RDH 7

U-values for IGUs U-value for a IGU is driven by the low-e coating emissivity, gas fill and gap width Lower emissivity coatings tend to be soft-coat silver Argon gas provides ~25% improvement in U-value Optimal gap is ~1/2 to 5/8 for air/argon - or so you would think U-factor (imperial) U-factor (imperial) 0.4 0.3 U-factor Versus Low-E Coating Emittance 0.2 0.04 0.08 0.12 0.16 0.2 0.24 Coating Emittance 0.32 0.30 0.28 0.26 0.24 Air U-factor Argon U-factor U-factor Versus Argon Fill Concentration 0.22 0 10 20 30 40 50 60 70 80 90 Argon Fill Concentration (%) IGU U-values Gap Widths and NFRC vs ISO NFRC (North American) and ISO (European) Standards do not agree on calculation procedures for center of glass U-values Outdoor temperature also matters (i.e. U-values are not fixed) Centre of Glass U-Value, W/m 2 -K 0.9 0.8 0.7 0.6 Triple Glazed IGU 2 Low-e Coatings U SI -0.71 U IP -0.125 (R-8) 0.5 10 12 14 16 18 20 22 24 Gap Size, mm U SI -0.52 U IP -0.092 (R-10.8) NFRC, -18 C NFRC, -7 C NFRC, 0 C NFRC, 5 C ISO, -18 C ISO, -7 C ISO, 0 C ISO, 5 C G.Finch - RDH 8

Overall Window U-values Center of Glazing U-value Edge of Glazing U-value Window U-value = Frame U-value x % Frame Area + Center of Glass U-value x % Glass Area + Edge of Glass U-value x % Edge of Glass Area Frame U-value (Operable & Fixed Frames) Overall R-value = 1/U-value Window ER Values ER Value is a numerical combination of the window U-value, SHGC and air-leakage rate for single family homes Aimed at consumers, higher number is better Used within NBC & Energy Star to incentivize better energy performance windows (lower U-value & higher SHGC) favoured) Better to use SHGC & U-value in the Far North G.Finch - RDH 9

Wading through the Technical Specs of IGUs Visible Light Center of Glass U-Factor Trans. Reflectance (Btu/hr/ft²/ F) Glass Temp (F) UV Tdw Clear % % Out % In SHGC SC Air Argon WinterSummer Trans ISO/CIE Indoor Clear IG 82% 15% 15% 0.78 0.89 0.48 0.46 45 90 58% 75% LoE Products - Sputtered Cardinal LoE²-272 #2 (e=.041) 72% 11% 12% 0.41 0.47 0.30 0.25 56 84 16% 55% Cardinal LoE²-272 #3 (e=.041) 72% 12% 11% 0.50 0.57 0.30 0.25 56 98 16% 55% Cardinal LoE²-270 #2 (e=.036) 70% 12% 13% 0.37 0.42 0.29 0.25 56 93 14% 53% Cardinal LoE²-270 #3 (e=.036) 70% 13% 12% 0.45 0.53 0.29 0.25 56 99 14% 53% Cardinal LoE 3-366 #2 (e=.022) 65% 11% 12% 0.27 0.31 0.29 0.24 56 83 5% 43% Cardinal LoE 3-366 #3 (e=.022) 65% 12% 11% 0.39 0.45 0.29 0.24 56 101 5% 43% PPG SolarBan 60#2 (e=.043) 71% 12% 13% 0.39 0.45 0.30 0.25 56 95 16% 53% Viracon VE-2000 #2(e=.040) 72% 11% 12% 0.38 0.44 0.26 0.25 56 84 11% 52% Guardian Perf. Plus ll #2(e=.044) 69% 19% 17% 0.41 0.47 0.30 0.25 56 65 20% 50% AFG Comfort TIAC #2(e=.036) 62% 23% 29% 0.40 0.46 0.29 0.25 56 85 30% 51% AFG Comfort TIR #2(e=.034) 71% 21% 19% 0.47 0.54 0.29 0.25 56 85 30% 57% AFG Comfort TIPS #3(e=.047) 77% 13% 14% 0.60 0.69 0.30 0.25 56 94 33% 63% LoE Products - Pyrolytic AFG Comfort E2 #3 (e=.204) 76% 16% 14% 0.73 0.85 0.35 0.31 53 101 44% 64% Pilk/LOF Energy Adv. #3,(e=.153) 75% 18% 17% 0.72 0.82 0.33 0.29 54 100 45% 65% Pilk/LOF Solar E #2(e=.153) 54% 10% 16% 0.48 0.55 0.33 0.29 54 91 40% 52% PPG Sungate 500 #3,(e=.215) 76% 18% 17% 0.71 0.81 0.35 0.31 52 99 49% 66% PPG Sungate 300 #3 (e=.324) 76% 18% 18% 0.71 0.82 0.38 0.34 51 96 56% 66% IGU Spacer Bars Lots of options look for lower conductivity & dual edge seal technology PIB primary seal (vapour), silicone secondary seal (structural) works well Avoid single seal systems Not all created equal G.Finch - RDH 10

Conduction through IGU Spacer Bars Failed IGUs from Bad Spacer Bar Choices G.Finch - RDH 11

Condensation & Frost Prevention Condensation/frost occurs when the surface temperature of the window drops below the dewpoint temperature of the surrounding air Causes: Inadequate window frames or IGU spacer bars Curtains or blocked interior airflow Poor installation of window frame Too high indoor dew-point Poor heating system configuration Condensation & Frost due to Hardware Problems G.Finch - RDH 12

Frost From Poor Window/Door Selection And Don t Forget to Close the Window.. G.Finch - RDH 13

Window Frame Design & Condensation Risk Every window has a slightly different condensation potential & many factors involved More conductive frame materials tend to be colder, but also bring heat from the frame to the edge glass Massing of frame material inboard or outboard of thermal break or IGU matters Operable units tend to perform worse than fixed units (frame profile & air leakage) IGU spacer bars matter for edge of glass & frame temperatures Glazing stop material also matters Glazing matters double vs triple glazing, low-e coating location, and interior surface low-e coatings Placement of window in rough opening can be important Frame Profile/Massing & Condensation Potential 1.7 C 11.4 C 5.0 C 5.3 C 4.3 C 7.4 C Exterior -18 C Interior 21 C G.Finch - RDH 14

Glazing Stops - PVC vs Aluminum with an Aluminum Frame Aluminum Glazing Stop PVC Glazing Stop 3.4 C 3.6 C -0.2 C 14.8 C 3.7 C 2.8 C Exterior -18 C Interior 21 C Window Frame Types & Condensation Potential Edge of IGU slightly warmer with aluminum Frame colder with aluminum Thermally Broken Aluminum Reinforced Vinyl Fiberglass Exterior -18 C Interior 21 C G.Finch - RDH 15

Frame Design Triple Glazed Vinyl 2.8 C 6.9 C Exterior -34 C Interior 21 C Wood vs Aluminum Curtainwall Subtle Tradeoffs Frame = R-2.6-1.9 C wood Warmer frame Exterior -18 C Interior 21 C 5.1 C Frame = R-2.0 Colder frame G.Finch - RDH 16

Double vs. Triple Glazing Exterior -18 C Interior 21 C Exterior -18 C Interior 21 C 2.6 C 8.9 C Condensation on the Exterior of Windows G.Finch - RDH 17

Rating Condensation Resistance of Windows Temperature Index (I-value) CSA A440 Measured in Lab coldest location Is value that can also be checked in the field - preferred Condensation Resistance Factor (CRF) AAMA Measured in Lab weighted cold location (relative metric) Condensation Resistance (CR) NFRC Simulated weighted factor accounting for range of indoor RH levels (30,50,70%) and fixed outdoor conditions All factors are different and cannot be correlated In all cases a higher number means a better product with lower potential for condensation Temperature Index (I-value) Measure of a window s condensation resistance (higher better) I-value = 100 x (T F - T O )/(T I T O ) T F = Frame temperature (worst), T I and T o = inside and outside temp. Can be used to help select windows based on exterior design conditions and interior RH expectations G.Finch - RDH 18

Selecting I-values by Winter Design Conditions Temperature Index (I) 100 90 80 70 60 50 40 30 20 10 0 Vancouver 60% Indoor RH 50% Indoor RH 40% Indoor RH 30% Indoor RH Edmonton 0-5 -10-15 -20-25 -30-35 -40-45 -50 January 2.5% Design Temperature Whitehorse Yellowknife Resolute CSA A440.2-2009 Other Considerations - Window Air-Leakage Rates Leakage occurs at frame joints/glazing interfaces, gaskets & operable hardware Air leakage ratings in CSA A440-00 and NAFS-08 Window Rating Max air leakage rate, m 3 /h/m CSA A440-00 Max air leakage rate, converted to L/s/m 2 NAFS-08 Max air leakage rate for R Class, L/s/m 2 (NFRC Standard Size Window) A1 2.79 1.86 n/a A2 1.65 1.10 1.5 A3 0.55 0.37 0.5 Fixed 0.25 0.17 0.2 G.Finch - RDH 19

Energy Codes & Available Windows in the North Energy Code Requirements & Regulations for Windows in the North NBC Part 9.36 (Houses) Zone 8 Maximum U-value U SI -1.4 (U IP -0.25) or minimum ER of 29 Is a vinyl, fiberglass or wood frame window with triple glazing (air filled non low-e) or argon filled double glazing with dual low-e coatings (#2 & #4 surfaces) Energy Star North Zone Maximum U-value of U SI -1.2 (U IP -0.21) and ER 24, OR minimum ER 34 NECB 2011 (Larger Buildings) Zone 8 Maximum U-value of U SI -1.6 (U IP -0.28) G.Finch - RDH 20

Additional Requirements Influencing Window Selection Yukon NBC 9.36 requirements adopted in April 2013 Whitehorse Green Building Standard Energuide 82 or better Whitehorse building bylaw maximum window U-value U SI - 1.4 (U IP -0.25) Northwest Territories Yellowknife Building Bylaw Energuide 80 or better home Typically see triple pane vinyl with argon and one low-e coating Nunavut Nunavut Housing Corporation minimum Energy Star Northern Zone, maximum U SI -1.2 (U IP -0.21) Local supply is more challenging that YT and NT with limited options and replacement parts etc. Northern Canada Window Suppliers and Local Preferences Vinyl framed triple glazed windows common for homes Apparently not a lot of U-value labelling happening - though understood that triple glazed vinyl or fiberglass meets code Seeing mix of argon filled non low-e triple glazing and argon filled dual low-e triple glazing Anecdotes of medium low solar heat gain being preferred and both northern and southern suppliers expressed doubt of merits for passive solar gains in the North concerns of overheating discomfort Anecdotes that sliding windows easier to maintain than crank operated casements (from remote communities) Interestingly quad-pane makes up 20-25% of local sales for one northern supplier Northern Suppliers Northerm (Whitehorse) and Arctic Front Windows (Hay River) Several Southern Supplies actively providing products Ply Gem, All Weather, Kohltech, JeldWen, Gentek, Cascadia G.Finch - RDH 21

Available Glazing Units Four major suppliers of low-e coated glass to the residential window industry: Cardinal, Guardian, PPG and AGC All make double and triple glazed units, harder to get quads made from major suppliers Each supplier has products available that can be categorized as having low, medium and high solar heat gain properties Minor costs differences between coatings and manufacturers Glazing cost is minor (~$5/sqft) compared to the overall cost of a window (avg $50/sqft in Yellowknife) Argon gas fill is fairly standard and often available at minimal cost Note about Hot2000 enter actual window properties from manufacturer do not let H2K calculate it Selecting Optimal Windows for Energy Efficiency G.Finch - RDH 22

Window Selection for Energy & Thermal Comfort Winter Goals Minimize heating energy Improve thermal comfort by reducing cold surfaces Low U-values, High SHGC Summer & Swing Season Goals Minimize overheating to prevent or reduce cooling needs Improve thermal comfort by reducing surface temperatures and indoor gains U-values not as important, Lower SHGC more valuable Optimal Window for Northern Housing Study performed by RDH with CMHC to look at optimal window selection for a representative northern housing archetype Above permafrost construction, single storey with heated crawlspace for services 1000 sq.ft house with 10% window to wall ratio While one archetype chosen here, the findings can be readily extrapolated to other and larger housing designs G.Finch - RDH 23

Energy Modeling Assumptions 4 occupants Standard NBC/NECB set-point and appliance/plug load assumptions unless more detailed northern modifications mde R-40 effective walls, R-60 roof, R-40 floor, 1.5ACH airtightness Oil heat & hot water (80% efficient) in NT/NU, electric in YT Ducted HRV, 60% efficient Starting window assumption, U SI -1.4 (U IP -0.25), SHGC 0.26 Modeling compared to NRCan benchmarks for similar homes DHW (Oil) 20% Room Electricity 5% Yellowknife $4800 Lighting 4% System Fans 0% DHW (Electricity) 34% Heating (Oil) 71% Room Electricity 12% Whitehorse $2400 Lighting 8% System Fans 0% Heating (Electricity) 46% Optimal Window Study Study Locations 2010 NBC CLIMATIC INFORMATION FOR NORTHERN LOCATIONS. Whitehorse Yellowknife Resolute Latitude 60.7 N 62.4 N 74.7 N Climate Zone 7B 8 8 Heating Degree Days (HDDs) 6580 8170 12360 January 2.5% Design Temperature -41 C -41 C -42 C Assumptions for modeling (2015): Electric heat in Whitehorse at $0.16/kWh Fuel oil in Yellowknife and Resolute at $1.17/L ($0.128/kWh) Easily scalable for other regions & fluctuating prices G.Finch - RDH 24

Impact of Window U-value as Only Variable Archetype home heating cost savings for various window U-values compared to the NBC 9.36 maximum U-value of 1.40 SI (0.25 IP) Annual Home Heating Cost Savings Whitehorse Yellowknife Resolute NBC 9.36 Maximum U-Value $300 $250 $200 $150 $100 $50 $- 0.8 -$50 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 -$100 Window U-Value (W/m 2 -K) (0.14) (0.18) (0.21) (0.25) (0.28) Impact of SHGC as Only Variable Archetype house heating cost savings for various window SHGC values compared to a baseline value of 0.26. Annual Home Heating Cost Savings Whitehorse Yellowknife Resolute NBC 9.36 Baseline SHGC $250 $200 $150 $100 $50 $- 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 -$50 -$100 Window Solar Heat Gain Coefficient (SHGC) G.Finch - RDH 25

Selecting Windows in the North Based on ER? Typical house heating cost savings for various window ER values compared to the NBC 9.36 baseline value of ER 29. Annual Home Heating Cost Savings $400 $300 $200 $100 $- -$100 -$200 Whitehorse Yellowknife Resolute NBC 9.36 Baseline ER 25 30 35 40 45 50 Energy Rating (ER) Note two different products with the same ER of 34 yield different heating energy consumption due to the differences in U-value and SHGC. Typical Northern Housing Window Combinations SAMPLE WINDOW PRODUCTS AVAILABLE & SUITABLE FOR CANADAS NORTH Configuration* Triple Glazed, Vinyl Frame, 1 Low-e Coating Triple Glazed, Vinyl Frame, 2 Low-e Coatings Triple Glazed, Fibreglass Frame, 2 Low-e Coatings Triple Glazed, Passive House Frame, 2 Low-e Coatings Quad Glazed, Vinyl Frame, 2 Low-e Coatings Low-E Coatings** Operable Unit Performance*** USI (W/m 2 -K) U-Value (Btu/hr-ft 2 -F) SHGC LoE 180 1.25 0.22 0.38 LoE 366 1.25 0.22 0.17 LoE 270 1.25 0.22 0.22 LoE 180/180 1.08 0.19 0.36 LoE 366/180 1.02 0.18 0.16 LoE 180/180 1.19 0.21 0.28 LoE 366/180 1.17 0.21 0.13 LoE 270/180 1.19 0.21 0.17 LoE 180/180 0.86 0.15 0.37 LoE 366/180 0.84 0.15 0.17 LoE 270/270 0.73 0.13 0.24 *All configurations include argon gas fill and warm edge spacers. **Low-emissivity glass from Cardinal line of products shown as an example; other glass manufacturer s products are available with similar performance characteristics. *** Performance characteristics shown are values calculated in accordance with NFRC 100 and 200 for operable configurations of actual products. All products operable units are casements, except Passive House units are tilt and turn. G.Finch - RDH 26

Archetypical House Heating Cost Differences Typical house heating cost savings relative to the highest U-value product (Vinyl frame with Cardinal LoE 366, U-0.22, SHGC 0.17). Annual Home Heating Cost Savings $350 $300 $250 $200 $150 $100 $50 $- -$50 Vinyl 366 Vinyl 180 Vinyl 270 Whitehorse Yellowknife Resolute Vinyl 180/180 Vinyl 366/180 Fibreglass 180/180 Fibreglass Fibreglass 366/180 270/180 Vinyl Passive House 180/180 Vinyl Quad Vinyl Passive 270/270 House 366/180 Influence of Window to Wall Ratio Typical change in home heating energy costs for various WWRs compared to a baseline value of 10% (U SI -1.40, SHGC-0.26). Annual Home Heating Cost Savings $200 $100 $- -$100 -$200 -$300 -$400 -$500 -$600 -$700 Whitehorse Yellowknife Resolute 5% 10% 15% 20% 25% 30% Window to Wall Ratio G.Finch - RDH 27

Influence of Window Orientation Typical change in home heating energy costs for windows facing various cardinal directions compared to a house with equal window area in all directions. Annual Home Heating Cost Savings $80 $60 $40 $20 $- -$20 -$40 -$60 -$80 -$100 -$120 Whitehorse Yellowknife Resolute West North East 0 45 90 135 180 225 270 315 360 Window Orientation (Degrees) Measured from South Benefits of Insulated Shutters Typical heating energy savings for a house with various exterior shutter configurations compared to a house without exterior shutters Annual Home Heating Cost Savings $90 $80 $70 $60 $50 $40 $30 $20 $10 $- Closed at Night, Loose Installation Insulated Whitehorse Insulated Yellowknife Insulated Resolute Closed at Night, Tight Installation Shutter Operation Uninsulated Whitehorse Uninsulated Yellowknife Uninsulated Resolute Closed Below -10 C, Loose Installation Closed below -10 C, Tight Installation Insulated shutters (R-11) versus uninsulated (R-1) are shown. Tight installation refers to shutters that are installed as airtight as possible against the wall or window; loose installation refers to cases where outdoor air bypasses the shutters. G.Finch - RDH 28

Selection of Windows for Comfort in the North Lower U-value windows will always be more comfortable and have less drafts than high U-value windows during the cold winter months Challenge is balancing the SHGC for the potential wintertime gain vs swing season/summer overheating Comfort can be difficult to quantify, however can look at window surface temperatures, air temperatures and operative temperatures Comfort Analysis & Glazing SHGC Selection Archetype Northern Home, West Zone Operative Temperature, June 21 st Example with windows closed/poor ventilation extreme case Temperature ( C) 40 38 36 34 32 30 28 26 Whitehorse Temperature ( C) 40 38 36 34 32 30 28 26 Yellowknife 24 1:00 3:00 5:00 7:00 9:00 11:00 13:00 15:00 17:00 19:00 21:00 23:00 24 1:00 3:00 5:00 7:00 9:00 11:00 13:00 15:00 17:00 19:00 21:00 23:00 SHGC 0.26, No Shutters SHGC 0.1, No Shutters SHGC 0.55, No Shutters SHGC 0.26, Shutter closed when direct sun SHGC 0.26, Shutters closed when indoor air temp is greater than 21 G.Finch - RDH 29

Comfort Analysis Window Surface Temperature & Operative Temperatures (Yellowknife) SHGC Selection for Comfort Optimal SHGC & risk for discomfort depends on number of factors: Window to wall ratio Higher window area = greater chance of overheating Window orientation West-facing windows pose greatest risk to overheating followed by east- and south-facing Potential for shading, type/operation of shading devices Overhangs, shutters, near-by trees or buildings reduce overheating potential If risk of overheating is high then suggest a lower SHGC window of 0.2 to 0.3 (will pay more for heating) If risk of overheating is low then suggest a higher SHGC window 0.4 or higher to reduce heating G.Finch - RDH 30

Summary: Window Design in Northern Canada Window design (amount and orientation) and product selection has significant impact on energy consumption & thermal comfort in Northern Homes Design a house with reasonable window to wall ratios (less than 15%), orient glazing primarily to south if possible and include exterior shading (overhangs, shutters, trees) Ask manufacturers for their product s U-value & SHGC Select the lowest possible U-value available, at least lower than U SI -1.4 (U IP -0.25) Assess risk of overheating and choose glazing with appropriate SHGC Low risk choose high SHGC >0.4 High risk choose lower SHGC 0.15 to 0.3 Discussion + Questions GFINCH@RDH.COM 604.873.1181 rdh.com buildingsciencelabs.com G.Finch - RDH 31