March 2018 – “To Breathe or to Stay Warm – That is the Question! – – or WUFI !”

March 2018 – “To Breathe or to Stay Warm – That is the Question! – – or WUFI !”

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Our CSI Chapter returned to the Thousand Oaks Golf Club where we visited last October to celebrate the Chapter’s 50th Anniversary.  Our presenters for this program were Amanda Gray and Gary Parsons of Dow Chemical in Midland.  Amanda is one of the newest members of CSI (joined Nov. 2017) and lives in Midland, MI.   She is also a member of ASHRAE, Women in Roofing, and is also the current Vice Chair of the Michigan Mason Contractor Association Board of Directors.  Gary Parsons is also a member of CSI, ASHRAE, RCI, and is a Research and Development Fellow for Dow Chemical where he has been employed since 1982.  Gary is the lead scientist of the Dow Building Science and Application Development Team where he provides technical oversight for Dow’s Building Sciences and Application Development Research Programs.  He is a licensed residential contractor in Michigan and uses his background in construction to perform the various research testing programs in accordance with “WUFI”.  WUFI is a German Language acronym for a software program,  “Warme Und Feuchtransport  Instationer” which roughly translates into English as “Transient Heat and Moisture Transport”.  The program calculates several parameters and tells how moisture and heat flow affect building materials over a period of time under actual real conditions.

 

As a residential builder, Gary has seen the problems of wood construction such as a) Thermal bridging through wood framing, b) Limiting factors of cavity insulation, and c) moisture issues of dew point condensation.  The same principals can also apply to masonry wall construction.  We have all seen the affect that dew point has on a cold container of your favorite beverage during hot humid weather conditions.  These water droplets form on the warm side of the can and run down the sides.  These same moisture conditions also occur inside cavity walls of wood and masonry wall construction under optimal conditions where indoor temperature is 70 degrees F, the relative humidity is at 30 percent, and outdoor temperature is 30 degrees F.  It’s not the material that causes this moisture to form on the sides of the container.  It is the drop in temperature that causes the condensation to form at the dew point (37.1 degrees F).  Gary approached Dow Chemical to build a series of homes next to each other using differing types of construction and with differing levels of occupancy income, where the company had no control of who lived in these homes.  A tract of property was selected in a residential area in the northeast of Midland near where highway US-10 makes the turn from an east-west direction to a north-south direction.

 

Four types of construction were chosen to follow existing codes, and possible future codes.  Each one of the houses were wired to transmit various weather and energy conditions directly to the research lab inside of Dow Chemical.  Specific codes included for construction were the 2006 IECC, 2012 IECC, 2012IECC-CI, and finally beyond 2012 IECC.  Due to Dow’s restrictive confidentiality codes, the actual street name and general location cannot be disclosed, however, street addresses for the 2006 IECC built houses were 5208, 5206, and 5204.  The addresses for the 2012 IECC built houses were 5200, 5118, and 5110.  The addresses for the 2012 IECC-CI built houses were 5106, 5102, and 5100.    The addresses for the beyond 2012 IECC built houses were 5019, 5016, and 5012.  The sun exposure direction was identical for all 12 houses.   Fiber insulation was used for the 2006 IECC and 2012 IECC homes and foam insulation was used for the 2012 IECC-CI and beyond 2012 IECC homes.   Within each code zone there were three similar sizes of homes built to include various sized families (small, medium, or large).  The occupants only knew that the sizes of the homes were similar but did not know under which code each house was built.  They paid rent to the landlord and did not have to worry about energy costs.  The test data was continually being monitored over a 5-year period of time and transmitted immediately to Dow Chemical where the various parameters of family living were known only to the landlord and to Dow.

 

Test data results showed that the comparison of air leakage per hour at 50 Pascals for the 2006 and 2012 homes was 2.8 air changes per hour (2006) and 3.1 air changes per hour (2012).   Air leakage for the 2012-CI and beyond 2012 were significantly lower at 2.2 air changes (2012-CI) and 1.8 air changes for the beyond 2012 house.  Bar charts for Above Grade Wall Temperature Difference showed that houses constructed with OSB/wrapped was 8.8 degrees from interior to exterior.  Houses constructed with R5 continuous insulation had a 17.6 degree difference from interior to exterior.  Houses constructed with R10 continuous insulation had a 21.2 degree difference from interior to exterior.  Moisture content for all houses varied greatly from the different type of construction simply because the families living in them had no control parameters for their individual life styles.

The summer of 2015 included detailed forensic inspections for several of the houses specifically for moisture content.  Houses No 2, 3, and 6 showed severe elevated moisture content while House No. 5 was always below 20 percent.  Afterwards, it became known that the occupant of House No. 5 was an elderly widow who lived very moderately and frugally.  The inspections included visual observation, sampling of OSB for strength measurement, and were swabbed for fungal or microbial growth (including microscopy).  House No. 2 had elevated moisture content, water stained cavities, no evidence of water in rim joists, and moderate to heavy fungal growth in the wall cavity.  House No. 3 also had elevated moisture content, small area of dark staining, no evidence of water, and some fungal growth in the rim joists.  House No. 6 had elevated moisture content, no evidence of water, some staining on joist bottom chord, and some fungal growth in the rim joists.  House No. 5 had low moisture content, very little water staining in the cavity, rust on staples, and no fungal growth.

 

Modeling predictions using the WUFI Parameters showed the following results:

 

RELATIVE HUMIDITY (adjusted for occupants)

House No. Predicted Winter Avg. Measured Winter Avg. Predicted Summer Avg. Measured Summer Avg.
1 42 29 60 39
3 43 29 60 59
5 22 17 60 51
9 25 23 60 49

 

 

SHEATHING MOISTURE (under ASHRAE 160)

Measured Sheathing Moisture Measured Moisture WUFI Predicted Sheathing Moisture WUFI Predicted Sheathing Moisture and Measured RH
House Nos. Maximum Pct. (Meas.) Number of Days   > 20% Maximum Pct. Number of Days   >20%
1 – 3 31 % 71 +/-  35 50% 190
4 – 6 29 % 42 +/- 35 19% 0
7 – 9 23 % 5 +/- 5 12% 0

 

 

SHEATHING MOISTURE (using Measured RH)

Measured Moisture Measured Moisture WUFI Predicted (ASHRAE 160) WUFI Predicted
House Nos. Maximum Pct. (Meas.) Number of Days   > 20% Maximum Pct. Number of Days   >20%
1 – 3 31 % 71 +/-  35 29% 46
4 – 6 29 % 42 +/- 35 14% 0
7 – 9 23 % 5 +/- 5 12% 0

 

Without divulging the exact addresses and types of house construction (due to the Dow restrictive confidentiality codes), I am allowed to give general construction data for a couple of typical walls.  Wall Type 2-R5-CI consisted of 1/2″gypsum board, 2×4 wood framing, R15 Kraft faced fiberglass batt insulation, rim joists were insulated with R19 Kraft faced batt insulation, 7/16″ OSB sheathing, R5 Styrofoam and cultured stone or vinyl siding.  Wall Type 3a House-wrap consisted of 1/2″ gypsum board, 2×6 wood framing, R19 Kraft faced fiberglass batt insulation, rim joists were insulated with R19 Kraft faced fiberglass batt insulation, 7/16″ OSB sheathing, spun bond polyolefin house wrap, and cultured stone or vinyl siding.

 

Unfortunately, the names of CSI members and guests at this meeting cannot be given because a part of this article was written while my wife was undergoing a heart procedure at the Meijer Heart Center and the Maintenance Staff accidently tossed away the listing of attendees and could not be retrieved.

Author: Jim Hojnacki

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