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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Passive House in California: Overkill or Appropriate?
- 1. Passive House in California: Overkill or Appropriate? Bronwyn Barry, Assoc.AIA Certified Passive House Consultant Director, One Sky Homes COPYRIGHT ONE SKY HOMES 2013
- 2. Agenda: T-24 Comparisons Assemblies that work What really matters? Glazing over the details
- 3. Nominal vs Actual 24’-0” wall = 288” (100%) 2x6 @ 16” o.c. (18) = 27” ( 10%) Batt Insulation = 261” ( 90%) Nominal Actual R-Value/inch Whole Wall 85/15% 75/25% Studs 1.3 7.0 1.1 1.8 Batts 3.5 19.3 16.4 14.4 Total Wall 17.4 16.2
- 4. The Sunnyvale Retrofit 0 10 20 30 40 50 60 70 80 90 100 Windows Walls Roof Floor Total Typical T-24 Project R- value (hr.ft2F/BTU.in) PH Project R-value (hr.ft2F/BTU.in) Windows: Alpen Walls: 2x4, cellulose w/ 2” Polyiso Roof: 6” Polyiso Floor: 4” Polyiso
- 5. Sunnyvale Retrofit Assembly Details FOUNDATION & BARGE RAFTER ROOF: R-40 WALLS: R- 23 WINDOWS: R-5 FLOOR: R-40 COPYRIGHT ONE SKY HOMES 2013
- 6. The SIPS New Build 0 10 20 30 40 50 60 70 80 Windows Walls Roof Floor Total Typical T-24 Project R- value (hr.ft2°F/BTU.in) PH Project R-value (hr.ft2°F/BTU.in) Windows: EnerSign Walls: 8” SIPS Roof: 10” SIPS Floor: Slab with 2”EPS
- 7. Stick Frame Net Zero 0 10 20 30 40 50 60 70 80 90 100 Windows Walls Roof Floor Total Typical T-24 Project R- value (hr.ft2F/BTU.in) PH Project R-value (hr.ft2F/BTU.in) Windows: Alpen + Sorpetaler Walls: 2x6, cellulose w/ 1” EPS Roof: 13” Truss, Cellulose Floor: Slab, 4” EPS
- 8. Cottle ZEH - Assembly Details Foundation - R-23 ICF Stem Wall R-15 Slab Floor Walls – R23 Ceiling - R-50 Loose-fill Cellulose
- 9. 1. Super-Insulate 2. Avoid Thermal Bridges 3. Air Seal ( tight! ) 4. Windows/Doors – high-performance 5. Heat Recovery Ventilation (HRV) in most Climates 6. Solar aware design 7. Use PHPP Passive House Recipe " Buildings heated with hair dryers"
- 10. Envelope Results kBTU/ft2.yr heating energy Preliminary Aug 3, 2009 Max. allowed = 4.75 kBTU/ft2.yr SIP wall system** Prefab Stud wall Site built 5.5" 7.25" 5.5" 5.5" w/ rigid insul. 7.25" 7.25" w/ rigid insul. 9.5" TJI studs Window Est. Cost ($K) 49 52 47 53 49 55 79 Sierra Pacific* 4.52 4.01 5.11 4.58 4.54 4.19 3.91 37 86 89 84 90 86 92 116 **assuming $4k for interior furring using Recoup 200DX HRV w/ 3' OA duct runs 4" EPS under slab 11-7/8" TJI roof 4" EPS slab edge Challenging walls Source: Performance analysis from Dan Johnson, Arkin Tilt Architects and cost estimates from Quantum Builders A dozen ways to build a wall
- 11. Floor to floor assembly with open web hanging floor truss Complicated junctionsHundreds of ways to mess them up!
- 12. Which details really matter? Air-sealing? Insulation? Ventilation? Thermal Bridges? or Windows? SILL & JAMB (CASEMENT)
- 13. The Sunnyvale Losses Exterior Walls 21% Roof 17% Floors 21% Windows 30% Exterior Door 2% Ventilation 9% Total Heat Losses = 15,170 kBTU/yr Windows: Alpen Walls: 2x4, cellulose w/ 2” Polyiso Roof: 6” Polyiso Floor: 4” Polyiso
- 14. The Sunnyvale Gains Windows: Alpen Walls: 2x4, cellulose w/ 2” Polyiso Roof: 6” Polyiso Floor: 4” Polyiso Windows (Solar gains) 50%Internal Heat Gains 50% Total Heat Gains = 7,748 kBTU/yr Losses 66% Gains 34% Annual Heat Demand = 7,556 kBTU/yr = 4.85 kBTU/sf.yr
- 15. The Cottle Losses Exterior Walls 32% Roof 9% Floors 12% Fndn Stem wall 1% Attached Garage 7% Windows 26% Ventilation 13% Total Heat Losses = 28,986 kBTU/yr Windows: Alpen + Sorpetaler Walls: 2x6, cellulose w/ 1” EPS Roof: 13” Truss, Cellulose Floor: Slab, 4” EPS
- 16. The Cottle Gains Windows: Alpen + Sorpetaler Walls: 2x6, cellulose w/ 1” EPS Roof: 13” Truss, Cellulose Floor: Slab, 4” EPS Total Heat Gains = 19,853 kBTU/yr Windows (Solar gains) Internal Heat Gains Losses 59% Gains 41% Annual Heat Demand = 9,133 kBTU/yr = 3.67 kBTU/sf.yr
- 17. Image: Lorna Fear IR images The Camera Never Lies!
- 18. Upcoming Wednesday, March 20th Pacific Energy Center San Francisco www.co2zeroca.org
- 19. More from Mark…. Questions? Thank You Bronwyn Barry Resources: www.passivehousecal.org www.aphnetwork.org www.passivehouse.com
Editor's Notes
- 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.