Passive House in California: Overkill or Appropriate?

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A close look at two recent California Passive House projects, one new, one retrofit. Which details matter in high performance new and retrofit construction and how we can use this information to build NZE and near-zero energy homes in California.

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  • An early project I contributed to with a comprehensive cost/benefit analysis of multiple wall assemblies, and multiple window packages. (Only one window package included here for simplicty.) Based on these analyses, the choice was made to use a balloon-framed 2x8 wall assembly. In the field, the benefits of this option started to deteriorate due to difficulty of raising tall, deep walls on site and a number of places where the insulation thickness became compromised.
  • Fun with THERM
  • This conclusion is easily backed up with this IR camera view of the project just completed in San Jose – 3-pane upstairs, US-made 3-pane downtairs – poor spacers set closer together.
  • Passive House in California: Overkill or Appropriate?

    1. 1. Passive House in California:Overkill or Appropriate?Bronwyn Barry, Assoc.AIACertified Passive House ConsultantDirector, One Sky HomesCOPYRIGHT ONE SKY HOMES 2013
    2. 2. Agenda:T-24 ComparisonsAssemblies that workWhat really matters?Glazing over the details
    3. 3. Nominal vs Actual24’-0” wall = 288” (100%)2x6 @ 16” o.c. (18) = 27” ( 10%)Batt Insulation = 261” ( 90%)Nominal ActualR-Value/inch Whole Wall 85/15% 75/25%Studs 1.3 7.0 1.1 1.8Batts 3.5 19.3 16.4 14.4Total Wall 17.4 16.2
    4. 4. The Sunnyvale Retrofit0102030405060708090100Windows Walls Roof Floor TotalTypical T-24 Project R-value (hr.ft2F/BTU.in)PH Project R-value(hr.ft2F/BTU.in)Windows: AlpenWalls: 2x4, cellulosew/ 2” PolyisoRoof: 6” PolyisoFloor: 4” Polyiso
    5. 5. Sunnyvale Retrofit Assembly DetailsFOUNDATION & BARGE RAFTERROOF: R-40WALLS: R- 23WINDOWS: R-5FLOOR: R-40COPYRIGHT ONE SKY HOMES 2013
    6. 6. The SIPS New Build01020304050607080Windows Walls Roof Floor TotalTypical T-24 Project R-value (hr.ft2°F/BTU.in)PH Project R-value(hr.ft2°F/BTU.in)Windows: EnerSignWalls: 8” SIPSRoof: 10” SIPSFloor: Slab with 2”EPS
    7. 7. Stick Frame Net Zero0102030405060708090100Windows Walls Roof Floor TotalTypical T-24 Project R-value (hr.ft2F/BTU.in)PH Project R-value(hr.ft2F/BTU.in)Windows: Alpen +SorpetalerWalls: 2x6, cellulosew/ 1” EPSRoof: 13” Truss, CelluloseFloor: Slab, 4” EPS
    8. 8. Cottle ZEH - Assembly DetailsFoundation - R-23 ICF Stem WallR-15 Slab FloorWalls – R23Ceiling - R-50 Loose-fill Cellulose
    9. 9. 1. Super-Insulate2. Avoid Thermal Bridges3. Air Seal ( tight! )4. Windows/Doors – high-performance5. Heat Recovery Ventilation (HRV) in mostClimates6. Solar aware design7. Use PHPPPassive House Recipe" Buildings heated with hair dryers"
    10. 10. Envelope Results kBTU/ft2.yr heating energyPreliminary Aug 3, 2009 Max. allowed = 4.75 kBTU/ft2.yrSIP wall system** Prefab Stud wall Site built5.5" 7.25" 5.5"5.5" w/ rigidinsul. 7.25"7.25" w/rigid insul.9.5" TJIstudsWindow Est. Cost ($K) 49 52 47 53 49 55 79Sierra Pacific* 4.52 4.01 5.11 4.58 4.54 4.19 3.9137 86 89 84 90 86 92 116**assuming $4k for interior furringusing Recoup 200DX HRV w/ 3 OA duct runs4" EPS under slab11-7/8" TJI roof4" EPS slab edgeChallenging wallsSource: Performance analysis from Dan Johnson, Arkin Tilt Architects and cost estimates from Quantum BuildersA dozen ways to build a wall
    11. 11. Floor to floor assembly withopen web hanging floor trussComplicated junctionsHundreds of ways to mess them up!
    12. 12. Which details really matter?Air-sealing?Insulation?Ventilation?Thermal Bridges?orWindows?SILL & JAMB (CASEMENT)
    13. 13. The Sunnyvale LossesExterior Walls21%Roof17%Floors21%Windows30%Exterior Door2%Ventilation9%Total Heat Losses = 15,170 kBTU/yrWindows: AlpenWalls: 2x4, cellulosew/ 2” PolyisoRoof: 6” PolyisoFloor: 4” Polyiso
    14. 14. The Sunnyvale GainsWindows: AlpenWalls: 2x4, cellulosew/ 2” PolyisoRoof: 6” PolyisoFloor: 4” PolyisoWindows(Solar gains)50%Internal HeatGains50%Total Heat Gains = 7,748 kBTU/yrLosses66%Gains34%Annual Heat Demand =7,556 kBTU/yr= 4.85 kBTU/sf.yr
    15. 15. The Cottle LossesExterior Walls32%Roof9%Floors12%Fndn Stem wall1%AttachedGarage7%Windows26%Ventilation13%Total Heat Losses = 28,986 kBTU/yrWindows: Alpen +SorpetalerWalls: 2x6, cellulosew/ 1” EPSRoof: 13” Truss, CelluloseFloor: Slab, 4” EPS
    16. 16. The Cottle GainsWindows: Alpen +SorpetalerWalls: 2x6, cellulosew/ 1” EPSRoof: 13” Truss, CelluloseFloor: Slab, 4” EPSTotal Heat Gains = 19,853 kBTU/yrWindows (Solar gains)Internal Heat GainsLosses59%Gains41%Annual Heat Demand = 9,133kBTU/yr= 3.67 kBTU/sf.yr
    17. 17. Image: Lorna Fear IR imagesThe Camera Never Lies!
    18. 18. UpcomingWednesday, March 20thPacific Energy CenterSan Franciscowww.co2zeroca.org
    19. 19. More from Mark….Questions?Thank YouBronwyn BarryResources:www.passivehousecal.orgwww.aphnetwork.orgwww.passivehouse.com

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