1. Understanding Moisture and Energy Movement Through the Building Envelope

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Agenda
Overview of Building Elements – Walls
Modeling Comparison of Prescriptive Assemblies
Above Grade
Below Grade
Case Study
5-Year -12 Home Research
Vancouver Research
Midland Test Hut Research
Summary
Q & A
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3. Building Elements Overview
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Structural Element
We build buildings to keep the outside out and the inside in. Therefore, we start with a structure designed to resist all the imposed loads such as live & dead loads, and all the environmental loads. While we start with the Structural Element, it is not the topic of this presentation. This presentation is about understanding the moisture and energy movement through the building. The next few slides are my attempt to mimic Joe Lstiburek’s method to explain the fundamental control layers. So, full credit to Joe Lstiburek for this elegantly simple way to diagram how buildings need to be designed to fulfill our expectations for building performance.
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5. Water Control Layer – Red Line
We protect our buildings with Control Layers. The most important of the four control layers is the Water Control Layer. Water destroys buildings and can affect occupants health. Water problems are the leading cause of lawsuits against builders. Therefore, it is imperative to have properly detailed first and second drainage plane to protect the building from bulk water damage. The water control layer must be continuous and surround the building entirely. Again, while the Water Control Layer is very important, it is not the topic of this presentation.
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6. Thermal Control Layer – Blue Line
The desire for Energy Conservation has led to Energy Codes which require increasing amounts of insulation. The thermal layer encloses the conditioned space slowing down the energy transfer to the exterior. We’re showing the thermal control layer at the ceiling but it could also be at the roof plane with an unvented roof strategy. As with the Water Control layer, the thermal control layer must also be continuous around the entire structure. The thermal control layer plays an important role in the prevention of condensation in our walls in addition to saving energy.
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7. Continuous Insulation vs Cavity Only
Here are IR images of the same floor plans taken within 10 minutes showing the value of continuous exterior insulation. The home on the left is 2x6 R-19 cavity insulation OSB and house wrap. The home on the right is 2x4 with R-16 cc SPF and R5.5 SIS. You can see the reduction in thermal bridging and reduction in energy loss across the entire wall.
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8. Air Control Layer – Green Line
It is well documented that 30-40% of the typical buildings’ energy is lost due to air leakage. If we are serious about saving energy we must make our building tighter and not leak energy. The air control layer also must be continuously connected. It is important that fibrous insulations must be in contact with an air barrier on all six sides in order to get the full r-value. The air control layer also plays important role in moisture management, because we know that most of the moisture transported into walls comes from air movement through the wall.
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9. Vapor Control Layer – Gold Line
The vapor control layer regulates the amount of moisture vapor passing through building materials. This is known as vapor permeance. The interesting thing about vapor barriers is that their effectiveness is at the rate of area coverage. In other words, if your vapor barrier covers 95% of the wall area, it is 95% effective. It does not need to be continuous. It is very common in Canada to employ interior air barriers that also act as the interior vapor barrier. However with tightening air leakage requirements, it becomes increasingly difficult using interior air barriers. Which is why we are seeing a trend for exterior air barriers. When an exterior air barrier is used, there is no need for the meticulous air sealing detailing of the vapor barrier.
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10. System Effect on Performance
Thermal Control
Vapor Control
Air Control
The thermal, air and vapor control layers can be comprised of many different materials with varying properties. The key is that whatever combination of materials are selected, they need to work as a system to Save energy and prevent moisture problems in the wall that can lead to premature decay of the building and lead to potential health problems associated with mold growth.
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Energy & Moisture
Here’s why, as we improve the energy efficiency of our buildings, three things happen; 1) We slow down the transfer of energy through the wall which saves energy 2) make parts of the wall assembly colder meaning we increase the possibility of condensation. The colder it gets in the cavity the more likelihood that the dew point will be reached and moisture vapor in the cavity can condense. 3) Then to add insult to injury, when the walls do get wet, we have less energy available to dry them out. This is why we can’t just add more insulation to save energy. YOU MUST CONSIDER THE HOUSE AS A SYSTEM.
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12. Modeling Comparisons of Prescriptive Assmeblies
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13. Walls to Compare – Above Grade (AG)
We selected 3 wall assemblies (A1, A#, & A5) in Zone 1 assuming >92% AFUE efficient furnaces. We chose these as we suspect these may be the most popular, given current most common practice.
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Walls to Compare
A-1
A-5
A-3
Here’s a graphic of each of the three wall assemblies
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15. Dew Point Comparison – A1 AG Wall
Interior
Exterior
Temperature 22
-27
Humidity 35 75
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16. Dew Point Comparison – A5 AG Wall
Interior
Exterior
Temperature 22
-27
Humidity 35 75
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17. Dew Point Comparison – A3 AG Wall
Interior
Exterior
Temperature 22
-27
Humidity 35 75
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18. Walls to Compare – Below Grade (BG)
We selected 3 wall assemblies (A1, A#, & A5) in Zone 1 assuming >92% AFUE efficient furnaces. We chose these as we suspect these may be the most popular, given current most common practice.
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19. Walls to Compare – Below Grade
20ci ci
12 + 5ci
Here’s a graphic of each of the three wall assemblies
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20. Dew Point Comparison – 20ci FG+Poly
Condensation. Higher potential for air flow with fiberous insulation. You can successfully use fibrous insulation, you must be meticuluous in the detailing of the air and vapor barriers.
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21. Dew Point Comparison – 12 + 10 ci
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22. Dew Point Comparison – 12 + 5ci
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WUFI
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WUFI
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25. WUFI – Above Grade Comparison
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26. WUFI Comparison – Below Grade Walls
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27. Measured Performance Case Studies
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28. Comparison Cases N 2x4 R5 CI 2X6 OSB/HW Net Zero Ready Homes
48- Somerset
49-Kendall
50-Preston
51-Kendall
52-Somerset
53-Preston
2X6 OSB/HW
54-Preston
55-Somerset
56-Kendall
2x4 R5 CI
Net Zero Ready Homes N

29. 2012 IECC without & with Continuous Insulation
OSB Plus Housewrap
R-5 Continuous Insulation

30. Above Grade Wall Measurement Location

31. 2x6 OSB & HW

33. 2x4 R5 ci & R16 SPF

35. Rim Joist Measurement Location
Moisture Pins

36. Engineered Rim joist FG & HW

38. Engineered rim joist R5 ci & SPF

40. Forensic Selection of Houses
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41. Summer 2015 Forensic Inspections
Inspect Houses 2,3,6 - elevated measured moisture content
Inspect House 5 - measured moisture content always below 20%
Inspections
Visual Observation
Sampling of OSB for Strength Measurement
Swab for Fungal or Microbial Growth – including microscopy

43. House 2

44. House 5 Rim Joist
2011
2015

45. Summary Forensic Findings
Moisture
Content
Above Grade Wall
Rim Joist
Microbial Sampling
House 2
Elevated
Water staining in cavity
No evidence of water
Moderate to heavy fungal growth – wall cavity
House 3
Small area of dark staining
Some fungal growth – rim joist
House 6
Some staining on joist bottom chord
House 5
Low
Rust on staples
No fungal growth

46. So, Why do we see this – high MC but no real deterioration?

48. Research Huts with Exterior Foam
Midland MI
Vancouver BC

49. Exterior Foam Research in Vancouver
2x6 walls comparing 1.5 inch of STYROFOAM installed over OSB, compared to Building paper over OSB – Both with hard coat stucco.
Latex paint vapor barrier on inside of Foam wall (class II) , 6 mil poly interior vapor barrier on building paper wall (Class I)
Intentional wetting events 2 oz in the morning, 2 oz in the evening, over a one week period
Gauvin 2000 Construction and Building Science Corporation, Joe Lstiburek

50. Foam walls dryer in general and dry more quickly after wetting event.

51. Larkin Wall Assembly Research Facility
Exterior Foam Research in Michigan
EXAMPLE
Understand summer inward solar vapor drive impact on wood wall components
Comparing impermeable exterior insulation to permeable WRB
Wall Assemblies
Manufactured Stone plus Vinyl Siding
WRB = STYROFOAM or Low Perm Housewrap or Building Paper
Larkin Wall Assembly Research Facility

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