ASHRAE Journal - October 2024 - 16

COLUMN RESIDENTIAL APPLICATIONS
In this analysis, " pass " indicates a maximum exterior
sheathing moisture content within the proposed wall
assembly between 0 and 16 mass percent. A " risky "
assessment indicates that the maximum exterior
sheathing moisture content within the proposed wall
assembly is between 16 and 20 mass percent, while a
" fail " rating denotes an exterior sheathing moisture
content in excess of 20 mass percent.
The tool also calculates the wall system thermal
performance and compares it to the 2018 International
Energy Conservation Code minimum requirements for
that climate zone.5 At the bottom of the results page,
there is a section for durability and general guidance.
The durability guidance gives feedback to the user
about the moisture durability of the wall and provides
advice for improving the durability performance.
When appropriate, hyperlinks to informative PDFs
are provided to further educate the user. The general
guidance usually gives the user feedback when the wall
does not meet energy requirements of the building code.
When examining a retrofit situation, the tool will offer
a family of retrofit options that are durable. The user
can then select an option and view similar information
regarding the moisture durability and thermal
performance of both the existing and retrofitted wall.
The BSA also offers information concerning retrofits
beyond energy efficiency and moisture durability
under the " Pre-Assessments " tab on the home page.
Prior to investigating a retrofit, several issues need
to be considered. Knowing the condition of the wall
will help guide contractors and remodelers with
remediation efforts, design, material selection,
installation and inspection. Links to other websites
that detail pre-retrofit checklists are listed.
Information on roofs and attics, exterior walls,
windows and attachments, basements, crawlspaces,
foundations and airtightness are detailed. Additional
resources are cited for learning more about other
details of the building envelope.
The BSA also provides a one-stop-shop regarding
the topic of hygrothermal behavior of wall systems.
Information on trapped moisture, drainage planes, air
barriers, inward and outward vapor drives, vapor open
walls and concrete masonry walls are each summarized.
In addition to the resources above, several case studies
clarify some of the issues likely to be encountered when
retrofitting exterior walls.
16
ASHRAE JOURNAL ashrae.org O CTO B ER 2024
An Example
A residential property in Atlanta (Climate Zone 3A)
is being considered for a facelift, and improvement of
the energy efficiency of the walls is being considered.
The homeowner intends to replace the failed cladding
that has had a history of leaks and wants to replace the
cladding with brick. The 1970s-era house is comprised
of a cladding system, building paper, plywood exterior
sheathing and uninsulated 2 × 4 in. wood frame wall, no
vapor retarder, and gypsum board with several coats of
latex paint. To control costs, the owner chooses to limit
this retrofit to the exterior of the assembly. They will
consider the addition of cavity insulation as well as a
limited amount (1 in. [26 mm]) of continuous insulation
due to the limitations imposed by the overhang depth.
They read through the Pre-Assessment information.
Concerned about earlier leaks, they employ a contractor
to verify there are no existing conditions that preclude
an energy and cladding upgrade. Moisture levels in
the sheathings and studs are around 10% by weight,
and no evidence of structural damage or mold exists.
They input their existing wall assembly into the tool
(acrylic stucco, no air space, no continuous insulation,
building paper water-resistive barrier, plywood exterior
sheathing, 2 × 4, 16 in. [0.4 m] on center wood framing,
no cavity insulation, no interior vapor retarder and a
latex paint interior finish). Based on their remodeling
plans, they select the exterior retrofit option.
The tool provides them with 2,782 recommendations of
retrofit options that meet the criteria of being moisture
durable and energy efficient. On the recommendations
page, they choose a brick cladding, a drained/ventilated
air space (the contractor recommended this feature),
1 in. (26 mm) of any type of continuous insulation,
housewrap to replace the torn and tattered building
paper and a cavity-fill insulation (fiberglass/cellulose/
low density foam) to be injected through the exterior
sheathing prior to the retrofit. This reduces the number
of recommendations to the three depicted in Online
Figure 1 (for figures see tinyurl.com/JournalExtras). The
user selects from the Recommendations list foil-faced
polyisocyanurate as the continuous insulation material
and activates the Results screen by pressing on the radio
button. Online Figure 2 is the result page, which provides:
* An image of the retrofitted wall and a summary of
the existing wall construction and the components of
the wall system that will be updated during the retrofit
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ASHRAE Journal - October 2024

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