The Problem With and Solutions for Ventilated Attics

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Presentation from 30th RCI Annual Convention and Tradeshow in San Antonio, TX - March 9, 2015.
Peer reviewed paper and presentation covers review of current issues with ventilated attics in the Pacific Northwest with case studies, the latest research and potential solutions to address mold growth and other moisture issues.

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The Problem With and Solutions for Ventilated Attics

  1. 1. The Problems With and Solutions for Ventilated Attics RCI 30TH INTERNATIONAL CONVENTION - SAN ANTONIO, TX MARCH 9, 2015 GRAHAM FINCH, MASC, P.ENG – RDH BUILDING ENGINEERING LTD.
  2. 2. Presentation Overview  Current Issues with Ventilated Attics  Case Study of Repairs  Attic Roof Hut Research & Monitoring Study – Key Findings  Performance of Potential Solutions  Ongoing Research & Field Trials
  3. 3. An Obvious Problem
  4. 4. A Not So Obvious Problem
  5. 5. Influencers of Moisture Problems in Attics What influences attic moisture issues & what can we control by design?  Roof orientation (solar radiation)  Roof slope (solar radiation)  Roofing material/color  Adjacent buildings – shading  Trees – shading & debris  Outdoor climate  Indoor climate  Roof Leaks  Insulation R-value  Air leakage from house  Duct leakage in attic  Duct discharge location  Vent area and distribution  Sheathing durability  Roof maintenance  Other things
  6. 6. Where are we Seeing the Biggest Issues? • Air leakage (ceiling details) • Exhaust duct leaks & discharge location (roof, soffit, or wall) • Inadequate venting provisions (amount, vent location, or materials) • Outdoor moisture: night sky condensation on underside of sheathing • Wetting through shingles/roofing (tipping the moisture balance)
  7. 7. Influence of Solar Radiation & Night Sky Radiation
  8. 8. Industry Trends – Less Heat Flow into Ventilated Attic Spaces <1970’s attic construction with excessive air leakage and heat loss into the attic 1980’s to 1990’s attic construction with moderate air leakage and heat loss into the attic 2000’s attic construction with minimal air leakage and heat loss into the attic
  9. 9. Standard Faith-Based Ventilation Approach Air-sealing details, duct exhaust details often not provided & left up to the contractor
  10. 10. Alternates to Ventilated Attics Unvented Hot Roof (Sprayfoam applied to underside) Exterior Insulated & hybrid approaches
  11. 11. Typical Ventilated Attic Moisture & Mold Issues
  12. 12. Typical Issues – Impact of Orientation North = Soaked South (Partially Shaded) = Damp
  13. 13. The Localized Nature of Air Leakage Condensation
  14. 14. The Localized Nature of Leaking Penetrations
  15. 15. The Localized Nature of Outdoor Moisture Wetting & Night Sky Condensation
  16. 16. It Happens in Ventilated Low Slope & Cathedral Ceilings Too
  17. 17. Other Not So Great Ideas…
  18. 18. So When Does it Become a Problem?
  19. 19. So When Does it Become a Problem?
  20. 20. So When Does it Become a Problem?
  21. 21. Case Study: Two Steps Forward, One Step Backwards • 2007 investigation of 5 yr old large townhouse complex • Was experiencing all of the problems we were and still are currently seeing
  22. 22. An Assortment of Typical Issues – Exhaust Ducts
  23. 23. An Assortment of Typical Issues – Exhaust Duct Details
  24. 24. An Assortment of Issues – Inadequate Ridge ‘Vent’ Material Almost no effective net free area, 5 layers of filter fabric
  25. 25. An Assortment of Issues – Ceiling Air Leakage
  26. 26. Attic Remediation – 2 years Later
  27. 27. Full Review of Initial Contributing Factors, Air-sealing
  28. 28. Retrofit Ceiling Air Sealing - Sprayfoam
  29. 29. Ceiling Air Sealing – Poly Bags of Fun
  30. 30. Mold Remediation - Dry Ice Blasting
  31. 31. New Exhaust Vent Hoods & Attic Ridge Vents
  32. 32. 2 Years Later Again…
  33. 33. The Localized Nature of Wetting
  34. 34. Water Leaks Around Plugged Dryer Exhaust Ducts
  35. 35. Lack of Dryer Exhaust Duct Maintenance
  36. 36. Soffit Exhaust Vent Hood Configuration Issues
  37. 37. Air-Sealing Issues
  38. 38. Air-Sealing Issues
  39. 39. Questioning the Effectiveness of Dry Ice Blasting against Mold?
  40. 40. Water Seepage through Aged & Saturated Asphalt Shingles?
  41. 41. Key Findings from Field Investigations & Field Monitoring  Seeing widespread issues with mold growth in newer wood-frame attics in Pacific Northwest  Wetting is exceeding drying capacity provided by ventilation  Problem is most often NOT due to a lack of ventilation  Usual culprits of air-leakage condensation (leaky ceiling, leaky ducts & discharge point)  Also seeing supplemental exterior moisture sources (night sky condensation, rainwater seepage)
  42. 42. Field Monitoring Study
  43. 43. Research Study Premise  Controlled field monitoring study to isolate exterior wetting mechanisms from interior sources (air, vapour)  To specifically evaluate impact of orientation, slope (3:12, 4:12 and 6:12) & shingle underlay  Remove influence of air leakage or heat gain from house  Monitor the performance of surface treatments Typical ventilated attic construction with air leakage and heat loss into the attic Theoretical attic with no air leakage or heat loss into the attic and unrestricted ventilation – Study setup here
  44. 44. Concurrent Companion Research in Pacific Northwest  Homeowner Protection Office of BC  RDH – monitoring field conditions & controlled field study (covered here)  MH – monitoring of attic moisture levels and air- leakage from indoors into attic spaces  FP Innovations – monitoring of effectiveness of various surface treatments  BCIT – modeling of attic ventilation rates & moisture movement
  45. 45. Roof Test Hut Field Monitoring Setup a) 3:12 Slope roof with roofing felt underlay b) 4:12 Slope roof with roofing felt underlay c) 6:12 Slope roof with roofing felt underlay d) 3:12 Control roof with SAM underlay
  46. 46. Roof Test Hut Field Monitoring Setup
  47. 47. Monitoring Equipment & Sensors Moisture Content, Temperature, Relative Humidity and surface Condensation sensors – north and south slopes x 4 huts
  48. 48. Site Boundary Conditions
  49. 49. 0 5 10 15 20 25 30 09-2012 10-2012 11-2012 12-2012 01-2013 02-2013 03-2013 04-2013 05-2013 06-2013 07-2013 08-2013 09-2013 10-2013 11-2013 12-2013 01-2014 02-2014 03-2014 MoistureContent[%] MC-FULL-S-CONT MC-FULL-S-312 MC-FULL-S-412 MC-FULL-S-612 EMC (1 wk) Seasonal Roof Sheathing Moisture Contents EMC calculated - Hailwood and Horrobin (1946) 0 5 10 15 20 25 30 09-2012 10-2012 11-2012 12-2012 01-2013 02-2013 03-2013 04-2013 05-2013 06-2013 07-2013 08-2013 09-2013 10-2013 11-2013 12-2013 01-2014 02-2014 03-2014 MoistureContent[%] MC-FULL-N-CONT MC-FULL-N-312 MC-FULL-N-412 MC-FULL-N-612 EMC (1 wk)
  50. 50. Seasonal Average Moisture Contents 0 5 10 15 20 25 30 Fall 2012 Winter 2012/2013 Spring 2013 Summer 2013 Fall 2013 Winter 2013/2014 Spring 2014 MoistureContent(%) MC-FULL-N-CONT MC-FULL-S-CONT MC-FULL-N-312 MC-FULL-S-312 MC-FULL-N-412 MC-FULL-S-412 MC-FULL-N-612 MC-FULL-S-612
  51. 51. Long Term Impacts of Elevated Moisture Contents North 3:12 after 1 yr North 4:12 after 1 yr
  52. 52. Tracking Mold Growth TABLE 2: VITTANEN’S MOLD GROWTH INDEX DESCRIPTIONS INDEX GROWTH RATE DESCRIPTION 0 No growth Spores not activated 1 Small amounts of mold on surface (microscope) Initial stages of growth 2 <10% coverage of mold on surface (microscope) ___ 3 10% – 30% coverage of mold on surface (visual) New spores produced 4 30% – 70% coverage of mold on surface (visual) Moderate growth 5 >70% coverage of mold on surface (visual) Plenty of growth 6 Very heavy and tight growth Coverage around 100%
  53. 53. Tracking Mold Growth – Year 1
  54. 54. Why is the Sheathing Wet? What is the Mechanism? Night sky condensation! Radiative heat loss from roof surface to colder night sky
  55. 55. When Does it Occur?
  56. 56. When Does it Occur? 0 100 200 300 Oct 02 Oct 03 Oct 04 Oct 05 Oct 06 Sol Solar Radiation CONDENSE-Plywood-312 Increasin 0 5 10 15 20 25 30 Oct 02 Oct 03 Oct 04 Oct 05 Oct 06 MoistureContent[%]andTemperature[°C] Condensation 0 5 10 15 20 25 30 Oct 02 Oct 03 Oct 04 Oct 05 Oct 06 MoistureContent[%]andTemperature[°C] MC-FULL-N-312 MC-IN-SURF-N-312 T-IN-N-312-Plywood T-N-312-Embedded Outdoor - Temperature Outdoor - Dewpoint COND-N-312 Sheathing Solar Radiation Condensation
  57. 57. When Does it Occur on the Underside of the Sheathing? 0 100 200 300 400 Oct 02 Oct 03 Oct 04 Oct 05 Oct 06 SolarRa Solar Radiation CONDENSE-Plywood-312 IncreasingSurf 0 5 10 15 20 25 30 Oct 02 Oct 03 Oct 04 Oct 05 Oct 06 MoistureContent[%]andTemperature[°C] Condensation 0 5 10 15 20 25 30 Oct 02 Oct 03 Oct 04 Oct 05 Oct 06 MoistureContent[%]andTemperature[°C] MC-FULL-N-312 MC-IN-SURF-N-312 T-IN-N-312-Plywood T-N-312-Embedded Outdoor - Temperature Outdoor - Dewpoint COND-N-312 Sheathing Solar Radiation Condensation 0 100 200 300 400 500 600 700 800 900 1000 Oct 02 Oct 03 Oct 04 Oct 05 Oct 06 SolarRadiation[W/m2] Solar Radiation CONDENSE-Plywood-312 IncreasingSurfaceCondensation 25 30 perature[°C] 25 30 perature[°C] 0 100 200 Oct 02 Oct 03 Oct 04 Oct 05 Oct 06 Solar Radiation CONDENSE-Plywood-312 Incre 0 5 10 15 20 25 30 Oct 02 Oct 03 Oct 04 Oct 05 Oct 06 MoistureContent[%]andTemperature[°C] Condensation 0 5 10 15 20 25 30 Oct 02 Oct 03 Oct 04 Oct 05 Oct 06 MoistureContent[%]andTemperature[°C] MC-FULL-N-312 MC-IN-SURF-N-312 T-IN-N-312-Plywood T-N-312-Embedded Outdoor - Temperature Outdoor - Dewpoint COND-N-312 Sheathing Solar Radiation Condensation Dry Heavy Condensation Light Condensation Daily Solar Radiation Cycles
  58. 58. Some Nuances of Condensation on Plywood
  59. 59. Nuances of Mold Growth on Plywood Heartwood vs Sapwood
  60. 60. Monitoring Night Sky Cooling Impacts
  61. 61. Shingle & Sheathing Temperature Depressions – Night Sky Cooling 2.6 2.5 2.5 2.6 2.4 2.5 0.9 0.9 0.9 1.0 1.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 312-N 312-S 412-N* 412-S 612-N 612-S TemperatureDepressionfromAmbient (°C) Avg Shingle T Avg Interior Sheathing Surface T *412-N sheathing temperature unavailable due to sensor malfunction 4.5°F On top of shingles <2°F At interior of roof sheathing Average Shingle and Sheathing Temperature Depression compared to Ambient Temperature for Winter (December 1, 2013 to January 31, 2014).
  62. 62. Hours of Potential Condensation - Sheathing 0 100 200 300 400 500 600 700 800 0.00 0.25 0.50 0.75 1.00 1.25 1.50 North South HoursofPotentialCondensation TemperatueDepressionfromAmbient(°C) 3:12 Temp 4:12 Temp 6:12 Temp 3:12 Hours 4:12 Hours 6:12 Hours <2°F temperature drop 150 to 300 hours per year
  63. 63. On the Flip Side: Solar Heat Gain & Drying during the Day
  64. 64. On the Flip Side: Solar Heat Gain & Drying Potential 0 5 10 15 20 25 30 35 40 45 50 55 60 Aug 21 00:00 Aug 21 06:00 Aug 21 12:00 Aug 21 18:00 Aug 22 00:00 Temperature[°C] Temperatures - 3:12 and 6:12 Slope Roofs - Early Spring Conditions T-OUT-N-612-Shingle T-OUT-S-612-Shingle T-IN-N-612-Plywood T-IN-S-612-Plywood T-OUT-N-312-Shingle T-OUT-S-312-Shingle T-IN-N-312-Plywood T-IN-S-312-Plywood Outdoor - Dewpoint Outdoor - Temperature South Shingles 130 -140°F North Shingles 100-110°F Ambient Air up to 79°F South Sheathing = 98°F North Sheathing = 90°F
  65. 65. Shingle and Sheathing Temperature Rise – During the Winter 1.9 5.8 1.7 6.5 1.7 6.6 0.9 1.7 0.9 2.0 1.7 1.8 0 1 2 3 4 5 6 7 312-N 312-S 412-N 412-S 612-N 612-S TemperatureRiseFromAmbient(°C) Avg Shingle T Avg Interior Sheathing Surface T Shingle Surface Sheathing ~11°F ~4°F
  66. 66. Impact of Impermeable SAM vs Permeable Roofing Felt Underlay
  67. 67. 0 5 10 15 20 25 30 Oct 17 Nov 14 Dec 12 Jan 09 Feb 06 Mar 06 Apr 03 May 01 May 29 Jun 26 MoitsureContent(%) MC-OUT-S-CONT MC-OUT-S-312 South Slope - Fall to Spring Impermeable SAM vs Permeable Roofing Felt Underlay 0 5 10 15 20 25 30 Oct 17 Nov 14 Dec 12 Jan 09 Feb 06 Mar 06 Apr 03 May 01 May 29 Jun 26 MoitsureContent(%) MC-OUT-N-CONT MC-OUT-N-312 Permeable Felt Impermeable SAM North Slope - Fall to Spring
  68. 68. Okay But.. What Happens when Shingles Start to Leak/Seep - Long Term?
  69. 69. Key Findings – The Cause of the Problem in the Pacific Northwest  Roof sheathing in well ventilated attics (also soffits, canopies) experiences elevated moisture levels in winter  Occurs despite elimination of typical wetting mechanisms within attics (air leakage, duct leakage, rain water leaks etc.)  Moisture level is above equilibrium level indicating additional wetting sources  Night sky cooling causes wetting when sheathing drops below ambient dewpoint (few hundred hours per year) in attic  Difficult to stop it from occurring  Fungal growth occurs due elevated moisture and condensation on underside of sheathing  More fungal growth on north than south – drying matters, the heat from a ceiling above a house will also help too
  70. 70. Monitoring of Potential Mitigation Strategies  Vented underlayment – de- couple night sky radiation cooling effects  Surface treatments to kill & prevent fungal growth
  71. 71. Night Sky Radiation De-Coupler?  Vented shingle underlay installed in one roof in 2nd year of study  Purpose: try to de-couple night sky cooling effects from sheathing
  72. 72. Vented Underlay – The Double Edged Sword South Orientation – Vented Underlay vs Direct Applied Shingles 0 50 100 150 200 250 300 350 400 450 -5 0 5 10 15 20 25 Jan 16 Jan 17 Jan 18 SolarRadiation(W/m2) Temperature(°C) T-OUT-S-VENT (Shingles) T-IN-S-VENT (Sheathing) T-OUT-S-312 (Shingles) T-IN-S-312 (Sheathing) Outdoor T T-Drainmat-S-VENT Solar Radiation Shingles – direct applied Shingles – vent mat 12°F drop in shingle 3°F drop in sheathing
  73. 73. Vented Underlay – The Double Edged Sword 0 2 4 6 8 10 12 14 16 6 8 10 12 14 16 18 20 22 Day Night Avg Temperature(°C) MoistureContent(%) Spring VENT-N-MC VENT-S-MC 312-N-MC 312-S-MC VENT-N-T VENT-S-T 312-N-T 312-S-T Vent Normal North South North South Spring (March 1, 2013 to April 30, 2013) Diurnal Moisture Content (SURF) and Temperature Averages for North and South Oriented Vented and Control (Direct Applied Shingles) Roof Assemblies
  74. 74. Round 1 - Surface Treatment Application  4 huts x 2 orientations = 8 applications of each  Fungicides, Cleaners, Sealers › Boracol® 20-2 › Boracol® 20-2 BD › Bleach › Thompson’s WaterSeal® › Kilz® Paint  Wood Preservatives › Copper Naphthenate › Zinc Naphthenate
  75. 75. Wood Preservative & Fungicide Surface Treatments When Applied 1 Year Later Fungal Growth observed is Cladosporium
  76. 76. North vs South Orientation
  77. 77. Visual Assessment of Surface Treatment Efficacy VISUAL ASSESSMENT OF SURFACE TREATMENT EFFICACY Test Roof Surface Treatments (north left, south right) Sansin Boracol® 20-2 Copper Naphthenate Bleach Thompsons WaterSeal® Kilz®Paint Zinc Naphthenate Sansin Boracol® 20-2BD Control 3:12 4:12 6:12 VISUAL ASSESSMENT SCALE Pristine or very light fungal growth Moderate fungal growth Significant fungal growth Hence need for duplicate samples – slope not a big factor (heartwood vs sapwood is) In our experience Kilz® & Boracol® 20- 2BD while okay here after 2 years may not be best long term for fungal growth
  78. 78. Wood Preservative & Fungicide Surface Treatments The best decay fungicide (Boracol 20-2BD) & surface paint (Kilz) looked okay in years 1 and 2 – but not in year 3
  79. 79. A Caution with Surface Treatments
  80. 80. A Caution with Surface Treatments
  81. 81. A Caution with Surface Treatments
  82. 82. Summary – Mitigation Strategy Performance  Thermally de-coupling the exposed shingles from the sheathing did not work well  Did not significantly “warm” sheathing temperature at night  On flip-side – the sheathing did not get as hot during the day, so less drying and resulting prolonged wet periods  Surface treatments appear to be a potential viable solution if right product is developed - current products not quite effective (nor developed specifically for this application)  Concurrent work by FP to perform accelerated testing of some new biocides/fungicides  Ongoing monitoring at our huts to monitor long-term field performance of next generation treatments
  83. 83. Concurrent Fungicide/Biocide Research – FP Innovations Images courtesy FP Innovations  Developed an accelerated 12 week test method to evaluate new fungicides applied to wood products  Have already tested a handful of newly innovated & proprietary fungicides & coatings  A few promising formulations completely prevented mold growth  Follow-up with field testing
  84. 84. Round 2 - Field Trials & Monitoring of New Surface Treatments
  85. 85. Nine New Treatments Applied to Both Cleaned & Moldy Sheathing
  86. 86. Adapting Surface Treatments for the Field (Underside Application)
  87. 87. Ongoing Monitoring of New Surface Treatments Most Promising fungicide/biocide is water repelling & contains several “active” ingredients to prevent long term mold growth. Note it is not a wood preservative it is a fungicide Currently undergoing environmental testing & available soon?
  88. 88. What A Real Roof Leak Ends up Doing to Sheathing (6 Months)
  89. 89. Final Thoughts  Ventilated attics & roof assemblies ‘built to code’ are experiencing mold growth on underside of sheathing (plywood or OSB)  Wetting from night sky condensation and may be exacerbated by air leaks & water leaks  Hard to reliably stop night sky condensation  More ventilation makes it worse, less may also  Mold growth may be minor but perceived as risk  Could build other attic assemblies but unlikely to replace ventilated attics any time soon  Need to address durability & sensitivity of wood based sheathings to mold growth  Just make sure the fungicide is no more harmful to humans that the mold is
  90. 90.  rdh.com Discussion + Questions Graham Finch – gfinch@rdh.com – 604-873-1181

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